Unit conversion, explained by engineers
684 deep, practical guides for the conversions that trip people up in real work — turbo boost pressure, torque wrench units, fuel economy across regions, radiation dose, data rate confusion, and more. Every article is written by our engineering desk and reviewed against NIST SP 811 and the BIPM SI Brochure.
Angle
4 articlesA 15% Trail Is Steeper Than It Sounds
A trail marked '15% average grade' doesn't sound steep on paper. In the field it's a wall. Percent grade is rise over run, and small numbers mean big work.
Arcminutes and Arcseconds: The Sub-Degree Units Astronomy Actually Uses
1° = 60′ = 3600″. Jupiter subtends ~40″. The Hubble resolves 0.05″. Getting the prime/double-prime notation wrong makes a telescope aim at empty sky.
GPS Coordinates: Decimal Degrees vs DMS vs UTM
40.7128°N = 40°42'46"N. Google Maps takes both. UTM (meters) for surveying. Precision matters.
Radians, Degrees and Gradians: Which and When
Degrees for humans, radians for calculus, gradians for surveyors, mils for artillery. A pragmatic guide to picking the right angle unit and converting cleanly.
Area
7 articlesHome Size: sq ft vs sq m vs Marla vs Tsubo
1000 sq ft = 92.9 m². Global real estate uses local units: marla (25.29 m²), tsubo (3.31 m²), pyeong (3.31 m²).
Carpet Ordering: Sq Yards vs Sq Metres vs Broadloom Widths
12-ft broadloom = 3.66 m. 1 sq yd = 0.836 m². Rounding waste up front prevents 2-week reorder delays.
Square Feet and Square Meters in Real Estate
Apartments listed at 800 sq ft rarely convert to a round metric number. Here is the exact factor, and the local measurement conventions that shift the number by 10%.
Square Kilometers vs Square Miles: Country Size Comparisons
Every country reports its area in one unit and expects the reader to convert. Here is the exact factor and a set of mental anchors for country-scale comparisons.
Hectares and Acres for Farmers
Yield per acre and yield per hectare do not convert with a round factor. Here is the exact math and why bushels-per-acre and tonnes-per-hectare disagree by 40%.
Barns: The Unit Nuclear Physicists Named as a Joke
1 barn = 10⁻²⁸ m². Nuclear physicists named it because a uranium nucleus is 'as big as a barn' at that scale. Here is where the unit shows up and how to convert.
Acres, Hectares and the Surveyor's Chain
A hectare is 2.471 acres, an acre is 43,560 sq ft, and neither number is arbitrary. Here is how land measurement grew from oxen and rope into the modern cadastral system.
Automotive
30 articlesEV Efficiency: kWh/100mi to an L/100km Gasoline-Equivalent
EV efficiency: translating kWh/100mi into a gasoline-equivalent L/100km. The exact factor, one worked example, and the mistake that quietly skews it.
Towing Capacity: lb to kg for an Imported Trailer
Towing capacity: matching a US truck's lb rating to a metric trailer's kg spec. The exact factor, one worked example, and the mistake that quietly skews it.
Wheel Camber: Degrees to a Percent Slope Equivalent
Wheel camber angle: converting degrees to a percent tilt for a quick gut check. The exact factor, one worked example, and the mistake that quietly skews it.
Track Fuel: liters to US gallons
Convert liters to US gallons for track fuel using 1 L = 0.26417205236 US gal. Worked example, quick table, and the mistake that throws results off.
Brake Rotor Thickness: mm to Inches Against the Wear Spec
Brake rotor thickness: checking a metric micrometer reading against an inch minimum spec. The exact factor, one worked example, and the mistake that quietly…
Jerry Can: liters to US gallons
Convert liters to US gallons for jerry can using 1 L = 0.26417205236 US gal. Worked example, quick table, and the mistake that throws results off.
Fuel Injectors: cc/min to lb/hr Flow Rating
Fuel injector sizing: converting cc/min flow to lb/hr for tuning software. The exact factor, one worked example, and the mistake that quietly skews it.
Fuel Tank: liters to US gallons
Convert liters to US gallons for fuel tank using 1 L = 0.26417205236 US gal. Worked example, quick table, and the mistake that throws results off.
Trailer Limit: kilometers per hour to miles per hour
Convert kilometers per hour to miles per hour for trailer limit using 1 km/h = 0.6213711922 mph. Worked example, quick table, and the mistake that throws…
Battery CCA to Ah: A Rule-of-Thumb Conversion
Car battery CCA to Ah: why there's no exact factor, only a rule of thumb. The exact factor, one worked example, and the mistake that quietly skews it.
Wheel Bolt Pattern: Inches to mm (5x4.5 to 5x114.3)
Wheel bolt pattern: matching an inch spec to a metric aftermarket wheel. The exact factor, one worked example, and the mistake that quietly skews it.
Road Trip: kilometers per hour to miles per hour
Convert kilometers per hour to miles per hour for road trip using 1 km/h = 0.6213711922 mph. Worked example, quick table, and the mistake that throws…
Spark Plug Gap: Thousandths of an Inch to mm
Spark plug gap: setting a thousandths-of-an-inch spec with a metric feeler gauge. The exact factor, one worked example, and the mistake that quietly skews it.
Speedometer Check: kilometers per hour to miles per hour
Convert kilometers per hour to miles per hour for speedometer check using 1 km/h = 0.6213711922 mph. Worked example, quick table, and the mistake that…
Track Day: kilometers per hour to miles per hour
Convert kilometers per hour to miles per hour for track day using 1 km/h = 0.6213711922 mph. Worked example, quick table, and the mistake that throws…
Engine Oil Viscosity: cSt to Saybolt Universal Seconds
Engine oil viscosity: converting cSt to the older Saybolt (SUS) scale. The exact factor, one worked example, and the mistake that quietly skews it.
Tire Tread Depth: 32nds of an Inch to mm
Tire tread depth: reading a US gauge against a metric wear spec. The exact factor, one worked example, and the mistake that quietly skews it.
European Rental: kilometers per hour to miles per hour
Convert kilometers per hour to miles per hour for european rental using 1 km/h = 0.6213711922 mph. Worked example, quick table, and the mistake that throws…
Track Setup: bar to kilopascals
Convert bar to kilopascals for track setup using 1 bar = 100 kPa. Worked example, quick table, and the mistake that throws results off.
Trailer Tire: bar to kilopascals
Convert bar to kilopascals for trailer tire using 1 bar = 100 kPa. Worked example, quick table, and the mistake that throws results off.
Brake Caliper: newton-meters to pound-feet
Convert newton-meters to pound-feet for brake caliper using 1 N·m = 0.7375621493 lb·ft. Worked example, quick table, and the mistake that throws results off.
Motorcycle Tire: bar to kilopascals
Convert bar to kilopascals for motorcycle tire using 1 bar = 100 kPa. Worked example, quick table, and the mistake that throws results off.
Axle Nut: newton-meters to pound-feet
Convert newton-meters to pound-feet for axle nut using 1 N·m = 0.7375621493 lb·ft. Worked example, quick table, and the mistake that throws results off.
Spare Wheel: bar to kilopascals
Convert bar to kilopascals for spare wheel using 1 bar = 100 kPa. Worked example, quick table, and the mistake that throws results off.
Valve Cover: newton-meters to pound-feet
Convert newton-meters to pound-feet for valve cover using 1 N·m = 0.7375621493 lb·ft. Worked example, quick table, and the mistake that throws results off.
Cold Tire: bar to kilopascals
Convert bar to kilopascals for cold tire using 1 bar = 100 kPa. Worked example, quick table, and the mistake that throws results off.
Spark Plug: newton-meters to pound-feet
Convert newton-meters to pound-feet for spark plug using 1 N·m = 0.7375621493 lb·ft. Worked example, quick table, and the mistake that throws results off.
Wheel Lug: newton-meters to pound-feet
Convert newton-meters to pound-feet for wheel lug using 1 N·m = 0.7375621493 lb·ft. Worked example, quick table, and the mistake that throws results off.
Washer Fluid: liters to US gallons
Convert liters to US gallons for washer fluid using 1 L = 0.26417205236 US gal. Worked example, quick table, and the mistake that throws results off.
Coolant Mix: liters to US gallons
Convert liters to US gallons for coolant mix using 1 L = 0.26417205236 US gal. Worked example, quick table, and the mistake that throws results off.
Aviation
15 articlesAircraft Oxygen Bottles: psi Gauge to Bar
Aircraft oxygen bottles: reading a psi gauge against a bar-rated refill cart. The exact factor, one worked example, and the mistake that quietly skews it.
Altimeter Setting: inHg to hPa for International Flying
Altimeter setting: converting inHg to hPa when crossing into metric airspace. The exact factor, one worked example, and the mistake that quietly skews it.
Propeller Pitch: Inches to Blade Angle in Degrees
Propeller pitch: why an inch spec doesn't translate to one blade angle. The exact factor, one worked example, and the mistake that quietly skews it.
Deicing Fluid: Type IV Mix Ratio to Actual Glycol Volume
Aircraft deicing fluid: converting a Type IV mix ratio to actual glycol volume. The exact factor, one worked example, and the mistake that quietly skews it.
Hotel Kettle: liters to US fluid ounces
Convert liters to US fluid ounces for hotel kettle using 1 L = 33.814022702 US fl oz. Worked example, quick table, and the mistake that throws results off.
Climb Rate: fpm to m/s for International Charts
Climb rate: converting fpm to m/s for a metric performance chart. The exact factor, one worked example, and the mistake that quietly skews it.
Camping Flask: liters to US fluid ounces
Convert liters to US fluid ounces for camping flask using 1 L = 33.814022702 US fl oz. Worked example, quick table, and the mistake that throws results off.
Weight and Balance: Moment (lb-in) to Moment Index
Weight and balance: why aircraft use a moment index instead of raw lb-in numbers. The exact factor, one worked example, and the mistake that quietly skews it.
Baby Formula: liters to US fluid ounces
Convert liters to US fluid ounces for baby formula using 1 L = 33.814022702 US fl oz. Worked example, quick table, and the mistake that throws results off.
Crosswind Component: Wind Speed and Angle to Knots
Crosswind component: why it's a trig calculation, not a straight wind-speed reading. The exact factor, one worked example, and the mistake that quietly skews…
Duty Free Bottle: liters to US fluid ounces
Convert liters to US fluid ounces for duty free bottle using 1 L = 33.814022702 US fl oz. Worked example, quick table, and the mistake that throws results off.
Runway Length: Meters to Feet for US Pilots
Runway length: converting a metric airport chart to the feet US pilots think in. The exact factor, one worked example, and the mistake that quietly skews it.
Refill Bottle: liters to US fluid ounces
Convert liters to US fluid ounces for refill bottle using 1 L = 33.814022702 US fl oz. Worked example, quick table, and the mistake that throws results off.
Cabin Pressure Differential: psi to Equivalent Cabin Altitude
Cabin pressure: what a psi differential actually means in cabin altitude feet. The exact factor, one worked example, and the mistake that quietly skews it.
Aircraft Fuel: Jet A Density, lb to US Gallon
Aircraft fuel weight: converting Jet A gallons to pounds for weight and balance. The exact factor, one worked example, and the mistake that quietly skews it.
Blood glucose
1 articleBody composition
1 articleCapacitance
2 articlesµF, nF, pF: Capacitance Units for Real Circuits
1 µF = 1000 nF = 10⁶ pF. Bulk decoupling in µF; RF bypass in nF; timing and matching in pF. Off by a decade means broken circuit.
Farads and Microfarads: Reading Capacitor Codes
A '104' capacitor is 100 nF. Here is the three-digit EIA code and the F/µF/nF/pF ladder every electronics hobbyist needs.
Charge
5 articlesPower Bank Watt-Hours and the 100 Wh Airline Rule
A 20,000 mAh power bank can be under or over the 100 Wh carry-on limit depending on voltage. How to convert mAh to Wh, what 100 Wh and 160 Wh mean at the gate, and what to print for security.
Battery Capacity: mAh, Wh, and the 100 Wh Airline Limit
Wh = mAh × V / 1000. TSA/IATA cap carry-on lithium batteries at 100 Wh (or 160 Wh with airline approval). 20,000 mAh at 3.7 V = 74 Wh. 30,000 mAh at 3.7 V = 111 Wh — confiscated.
Battery Chemistry: LiFePO4 vs Lead-Acid Usable Wh
100 Ah lead-acid @ 50% DoD = 600 Wh usable. 100 Ah LiFePO4 @ 90% DoD = 1152 Wh — nearly 2× real energy.
Coulomb, mAh, Ah: Charge Units and Battery Capacity
1 A·h = 3600 C. A 3000 mAh phone battery is 10 800 C. Confusing energy (Wh) with charge (Ah) is the number one battery-spec error.
Amp-hours and Watt-hours: Battery Capacity Explained
A 100 Ah battery and a 100 Wh battery are not comparable. Here is why voltage matters and how to convert battery specs across chemistries.
Clothing sizes
1 articleConcentration
1 articleConcentration - solution
1 articleConcentration (molar)
1 articleConcentration Molar
1 articleConcentration-molar
3 articlespH Scale: [H⁺] in mol/L Explained
pH = -log₁₀[H⁺]. pH 4 = 10⁻⁴ M. Each unit is 10× — vinegar (2.4) is 4000× more acidic than tomato (4.6).
Cholesterol Units: mg/dL vs mmol/L
For cholesterol, mmol/L × 38.67 = mg/dL. Triglycerides use × 88.57. Different molecule, different factor.
Blood Glucose: mg/dL vs mmol/L — CGM Conversion Table
100 mg/dL = 5.55 mmol/L for glucose. Convert fasting, post-meal, and A1c targets between US and international units.
Concentration-solution
1 articleConstruction
20 articlesExcavation Slope Ratio: 1.5:1 to Percent Grade
Excavation slope ratios: converting 1.5:1 (H:V) into a percent grade. The exact factor, one worked example, and the mistake that quietly skews it.
Crane Load Charts: US Tons to Metric Tonnes
Crane load charts: don't trust a US ton rating against a metric tonne chart. The exact factor, one worked example, and the mistake that quietly skews it.
Stud Spacing: 16" and 24" On-Center to mm
Stud spacing: laying out 16 or 24 inch on-center framing with a metric tape. The exact factor, one worked example, and the mistake that quietly skews it.
Brick Count: Bricks per m² to Bricks per ft²
Brick count estimates: converting a per-m² rate to per-ft² for a US order sheet. The exact factor, one worked example, and the mistake that quietly skews it.
Gravel Tonnage: US Tons to Metric Tonnes per Load
Gravel tonnage: reconciling a US ton delivery ticket with a metric spec. The exact factor, one worked example, and the mistake that quietly skews it.
Cabinet Finish: US gallons to liters
Convert US gallons to liters for cabinet finish using 1 US gal = 3.785411784 L. Worked example, quick table, and the mistake that throws results off.
Roof Pitch: Inches-per-Foot to Percent Grade
Roof pitch: turning a 6:12 spec into a percent grade for drainage math. The exact factor, one worked example, and the mistake that quietly skews it.
Primer Order: US gallons to liters
Convert US gallons to liters for primer order using 1 US gal = 3.785411784 L. Worked example, quick table, and the mistake that throws results off.
Fence Sealer: US gallons to liters
Convert US gallons to liters for fence sealer using 1 US gal = 3.785411784 L. Worked example, quick table, and the mistake that throws results off.
Footing Frost Depth: Inches to cm by Climate Zone
Footing frost depth: converting a local inch requirement to cm for imported plans. The exact factor, one worked example, and the mistake that quietly skews it.
Rebar Size: US Bar Number to mm Diameter
Rebar size numbers: what a US #5 bar actually measures in millimeters. The exact factor, one worked example, and the mistake that quietly skews it.
Ceiling Paint: US gallons to liters
Convert US gallons to liters for ceiling paint using 1 US gal = 3.785411784 L. Worked example, quick table, and the mistake that throws results off.
Driveway Repair: cubic yards to cubic meters
Convert cubic yards to cubic meters for driveway repair using 1 yd³ = 0.76455485798 m³. Worked example, quick table, and the mistake that throws results off.
Deck Stain: US gallons to liters
Convert US gallons to liters for deck stain using 1 US gal = 3.785411784 L. Worked example, quick table, and the mistake that throws results off.
Concrete Bags: Per Cubic Yard vs Per Cubic Meter
Concrete bag counts: why 'bags per yard' doesn't match 'bags per meter'. The exact factor, one worked example, and the mistake that quietly skews it.
Fence Post Mix: cubic yards to cubic meters
Convert cubic yards to cubic meters for fence post mix using 1 yd³ = 0.76455485798 m³. Worked example, quick table, and the mistake that throws results off.
Garden Slab: cubic yards to cubic meters
Convert cubic yards to cubic meters for garden slab using 1 yd³ = 0.76455485798 m³. Worked example, quick table, and the mistake that throws results off.
Footing Trench: cubic yards to cubic meters
Convert cubic yards to cubic meters for footing trench using 1 yd³ = 0.76455485798 m³. Worked example, quick table, and the mistake that throws results off.
Patio Pour: cubic yards to cubic meters
Convert cubic yards to cubic meters for patio pour using 1 yd³ = 0.76455485798 m³. Worked example, quick table, and the mistake that throws results off.
Asphalt Lift Thickness: Inches to mm for Compaction Specs
Asphalt lift thickness: converting a US paving spec to mm for a metric roller. The exact factor, one worked example, and the mistake that quietly skews it.
Cooking
46 articlesButter Sticks, Cups, and Grams — US Baking Abroad
US butter sticks are 113 g (4 oz). European blocks are 250 g. Recipe says half cup butter — how many grams, tablespoons, and what to buy at a foreign supermarket.
Air Fryer Temp: The Offset from a Standard Oven
Air fryer temperature: why you can't use your oven's number as-is. The exact factor, one worked example, and the mistake that quietly skews it.
Medicine Spoon: US teaspoons to milliliters
Convert US teaspoons to milliliters for medicine spoon using 1 US tsp = 4.928921594 mL. Worked example, quick table, and the mistake that throws results off.
Pickle Brine: US quarts to liters
Convert US quarts to liters for pickle brine using 1 US qt = 0.946352946 L. Worked example, quick table, and the mistake that throws results off.
Candy Stages: Soft-Ball to Hard-Crack in F and C
Candy stages: hitting soft-ball to hard-crack on a Celsius thermometer. The exact factor, one worked example, and the mistake that quietly skews it.
Spice Rub: US teaspoons to milliliters
Convert US teaspoons to milliliters for spice rub using 1 US tsp = 4.928921594 mL. Worked example, quick table, and the mistake that throws results off.
Ice Cream Base: US quarts to liters
Convert US quarts to liters for ice cream base using 1 US qt = 0.946352946 L. Worked example, quick table, and the mistake that throws results off.
Espresso Pump Pressure: Bar to PSI on the Gauge
Espresso pump pressure: reading bar against a PSI-labeled gauge. The exact factor, one worked example, and the mistake that quietly skews it.
Yeast Proofing: US teaspoons to milliliters
Convert US teaspoons to milliliters for yeast proofing using 1 US tsp = 4.928921594 mL. Worked example, quick table, and the mistake that throws results off.
Steak Doneness: Internal Temp F to C by Stage
Steak doneness: matching internal temperature across F and C thermometers. The exact factor, one worked example, and the mistake that quietly skews it.
Stock Pot: US quarts to liters
Convert US quarts to liters for stock pot using 1 US qt = 0.946352946 L. Worked example, quick table, and the mistake that throws results off.
Wine Bottle Sizes: Standards to Magnums in mL
Wine bottle sizes: how many standards actually fit in a magnum. The exact factor, one worked example, and the mistake that quietly skews it.
Baking Soda: US teaspoons to milliliters
Convert US teaspoons to milliliters for baking soda using 1 US tsp = 4.928921594 mL. Worked example, quick table, and the mistake that throws results off.
Seafood Counter: pounds to kilograms
Convert pounds to kilograms for seafood counter using 1 lb = 0.45359237 kg. Worked example, quick table, and the mistake that throws results off.
Maple Glaze: US tablespoons to milliliters
Convert US tablespoons to milliliters for maple glaze using 1 US tbsp = 14.78676478 mL. Worked example, quick table, and the mistake that throws results off.
Pizza Dough Hydration: Percent to Grams of Water
Pizza dough hydration: turning a baker's percentage into real grams of water. The exact factor, one worked example, and the mistake that quietly skews it.
Potato Roast: pounds to kilograms
Convert pounds to kilograms for potato roast using 1 lb = 0.45359237 kg. Worked example, quick table, and the mistake that throws results off.
Hot Sauce Batch: US tablespoons to milliliters
Convert US tablespoons to milliliters for hot sauce batch using 1 US tbsp = 14.78676478 mL. Worked example, quick table, and the mistake that throws results…
Flour Sack: pounds to kilograms
Convert pounds to kilograms for flour sack using 1 lb = 0.45359237 kg. Worked example, quick table, and the mistake that throws results off.
Honey for Sugar: The Volume Substitution Ratio
Swapping honey for sugar without wrecking the batter's moisture. The exact factor, one worked example, and the mistake that quietly skews it.
Olive Oil Drizzle: US tablespoons to milliliters
Convert US tablespoons to milliliters for olive oil drizzle using 1 US tbsp = 14.78676478 mL. Worked example, quick table, and the mistake that throws…
Pulled Pork: pounds to kilograms
Convert pounds to kilograms for pulled pork using 1 lb = 0.45359237 kg. Worked example, quick table, and the mistake that throws results off.
Active Dry to Instant Yeast: Gram-for-Gram Swap
Active dry to instant yeast: the gram-for-gram swap that actually works. The exact factor, one worked example, and the mistake that quietly skews it.
Vanilla Extract: US tablespoons to milliliters
Convert US tablespoons to milliliters for vanilla extract using 1 US tbsp = 14.78676478 mL. Worked example, quick table, and the mistake that throws results…
Mason Jar Sauce: US pints to milliliters
Convert US pints to milliliters for mason jar sauce using 1 US pint = 473.176473 mL. Worked example, quick table, and the mistake that throws results off.
Brisket Order: pounds to kilograms
Convert pounds to kilograms for brisket order using 1 lb = 0.45359237 kg. Worked example, quick table, and the mistake that throws results off.
Brown Sugar: Packed Cups to Grams
Brown sugar: why a packed cup weighs so much more than you'd guess. The exact factor, one worked example, and the mistake that quietly skews it.
Marinade Mix: US tablespoons to milliliters
Convert US tablespoons to milliliters for marinade mix using 1 US tbsp = 14.78676478 mL. Worked example, quick table, and the mistake that throws results off.
Takeaway Soup: US pints to milliliters
Convert US pints to milliliters for takeaway soup using 1 US pint = 473.176473 mL. Worked example, quick table, and the mistake that throws results off.
Pasta Serving: ounces to grams
Convert ounces to grams for pasta serving using 1 oz = 28.349523125 g. Worked example, quick table, and the mistake that throws results off.
Gas Mark to Celsius: Reading a UK Oven Dial
Gas mark to Celsius: reading a UK oven dial without guessing. The exact factor, one worked example, and the mistake that quietly skews it.
Custard Batch: US pints to milliliters
Convert US pints to milliliters for custard batch using 1 US pint = 473.176473 mL. Worked example, quick table, and the mistake that throws results off.
Deli Turkey: ounces to grams
Convert ounces to grams for deli turkey using 1 oz = 28.349523125 g. Worked example, quick table, and the mistake that throws results off.
Smoothie Prep: US cups to milliliters
Convert US cups to milliliters for smoothie prep using 1 US cup = 236.5882365 mL. Worked example, quick table, and the mistake that throws results off.
Craft Beer Glass: US pints to milliliters
Convert US pints to milliliters for craft beer glass using 1 US pint = 473.176473 mL. Worked example, quick table, and the mistake that throws results off.
Coffee Beans: ounces to grams
Convert ounces to grams for coffee beans using 1 oz = 28.349523125 g. Worked example, quick table, and the mistake that throws results off.
Soup Batch: US cups to milliliters
Convert US cups to milliliters for soup batch using 1 US cup = 236.5882365 mL. Worked example, quick table, and the mistake that throws results off.
Berry Picking: US pints to milliliters
Convert US pints to milliliters for berry picking using 1 US pint = 473.176473 mL. Worked example, quick table, and the mistake that throws results off.
Chocolate Chips: ounces to grams
Convert ounces to grams for chocolate chips using 1 oz = 28.349523125 g. Worked example, quick table, and the mistake that throws results off.
Salad Dressing: US cups to milliliters
Convert US cups to milliliters for salad dressing using 1 US cup = 236.5882365 mL. Worked example, quick table, and the mistake that throws results off.
Meal Prep Chili: US quarts to liters
Convert US quarts to liters for meal prep chili using 1 US qt = 0.946352946 L. Worked example, quick table, and the mistake that throws results off.
Cheese Portion: ounces to grams
Convert ounces to grams for cheese portion using 1 oz = 28.349523125 g. Worked example, quick table, and the mistake that throws results off.
Rice Cooker Water: US cups to milliliters
Convert US cups to milliliters for rice cooker water using 1 US cup = 236.5882365 mL. Worked example, quick table, and the mistake that throws results off.
Cookie Icing: US teaspoons to milliliters
Convert US teaspoons to milliliters for cookie icing using 1 US tsp = 4.928921594 mL. Worked example, quick table, and the mistake that throws results off.
Lemonade Cooler: US quarts to liters
Convert US quarts to liters for lemonade cooler using 1 US qt = 0.946352946 L. Worked example, quick table, and the mistake that throws results off.
Pancake Batter: US cups to milliliters
Convert US cups to milliliters for pancake batter using 1 US cup = 236.5882365 mL. Worked example, quick table, and the mistake that throws results off.
Cooking / Mass:volume
1 articleCooking & Volume
1 articleCooking time
1 articleData
31 articlesColor Depth: Bits per Channel to Total Color Count
Color depth: why each extra bit doubles the palette, not adds to it. The exact factor, one worked example, and the mistake that quietly skews it.
Hash Rate: MH/s to GH/s for Mining Pool Stats
Hash rate units: converting MH/s to GH/s to match a pool's dashboard. The exact factor, one worked example, and the mistake that quietly skews it.
Frame Time: Converting FPS to Milliseconds per Frame
Frame time: why the jump from 60fps to 144fps matters less than it sounds. The exact factor, one worked example, and the mistake that quietly skews it.
PPI vs DPI: Same Number, Different Meaning
PPI vs DPI: why the number transfers but the concept doesn't. The exact factor, one worked example, and the mistake that quietly skews it.
RAM CAS Latency: Cycles to Nanoseconds (DDR4-3200)
RAM CAS latency: why 'CL16' means something different on every memory speed. The exact factor, one worked example, and the mistake that quietly skews it.
Photo Library: terabytes to gigabytes
Convert terabytes to gigabytes for photo library using 1 TB = 1000 GB (decimal). Worked example, quick table, and the mistake that throws results off.
Disk Sectors: 512-Byte Legacy vs 4K Advanced Format
Disk sectors: why '512-byte' and '4K' drives count blocks so differently. The exact factor, one worked example, and the mistake that quietly skews it.
A 7B Model Needs 14 GB of VRAM (Unless You Quantize)
The rule I use: model billions × 2 = VRAM gigabytes at fp16, or × 0.5 at 4-bit. A 13B model needs a 24 GB card at fp16, or fits on a 12 GB card quantized.
Database Snapshot: terabytes to gigabytes
Convert terabytes to gigabytes for database snapshot using 1 TB = 1000 GB (decimal). Worked example, quick table, and the mistake that throws results off.
Frame Rate Pulldown: 24fps Film to 30fps Video
3:2 pulldown: how 24fps film content becomes 30fps video. The exact factor, one worked example, and the mistake that quietly skews it.
Video Archive: terabytes to gigabytes
Convert terabytes to gigabytes for video archive using 1 TB = 1000 GB (decimal). Worked example, quick table, and the mistake that throws results off.
NAS Transfer: megabits per second to megabytes per second
Convert megabits per second to megabytes per second for nas transfer using 1 Mb/s = 0.125 MB/s. Worked example, quick table, and the mistake that throws…
Office WiFi: megabits per second to megabytes per second
Convert megabits per second to megabytes per second for office wifi using 1 Mb/s = 0.125 MB/s. Worked example, quick table, and the mistake that throws…
Camera Upload: megabits per second to megabytes per second
Convert megabits per second to megabytes per second for camera upload using 1 Mb/s = 0.125 MB/s. Worked example, quick table, and the mistake that throws…
Baud Rate to bps: Why They're Not the Same Number
Baud rate to bps: the modulation scheme is the missing piece. The exact factor, one worked example, and the mistake that quietly skews it.
Game Patch: megabits per second to megabytes per second
Convert megabits per second to megabytes per second for game patch using 1 Mb/s = 0.125 MB/s. Worked example, quick table, and the mistake that throws…
CPU Clock Speed: MHz to GHz for an Overclocking Log
CPU clock speed: converting MHz BIOS readouts to the GHz you actually track. The exact factor, one worked example, and the mistake that quietly skews it.
Fiber Plan: megabits per second to megabytes per second
Convert megabits per second to megabytes per second for fiber plan using 1 Mb/s = 0.125 MB/s. Worked example, quick table, and the mistake that throws…
Compression Ratio: 4:1 to Actual File Size Saved
File compression ratio: turning a 4:1 claim into real megabytes saved. The exact factor, one worked example, and the mistake that quietly skews it.
NAS Array: gigabytes to gibibytes
Convert gigabytes to gibibytes for nas array using 1 GB (decimal) = 0.93132257462 GiB. Worked example, quick table, and the mistake that throws results off.
Game Download: gigabytes to gibibytes
Convert gigabytes to gibibytes for game download using 1 GB (decimal) = 0.93132257462 GiB. Worked example, quick table, and the mistake that throws results off.
Phone Video: gigabytes to gibibytes
Convert gigabytes to gibibytes for phone video using 1 GB (decimal) = 0.93132257462 GiB. Worked example, quick table, and the mistake that throws results off.
Cloud Backup: gigabytes to gibibytes
Convert gigabytes to gibibytes for cloud backup using 1 GB (decimal) = 0.93132257462 GiB. Worked example, quick table, and the mistake that throws results off.
Design Files: terabytes to gigabytes
Convert terabytes to gigabytes for design files using 1 TB = 1000 GB (decimal). Worked example, quick table, and the mistake that throws results off.
Laptop SSD: gigabytes to gibibytes
Convert gigabytes to gibibytes for laptop ssd using 1 GB (decimal) = 0.93132257462 GiB. Worked example, quick table, and the mistake that throws results off.
Phone Storage: '128 GB' vs Actual Usable Space
128 GB advertised = 128,000,000,000 bytes = 119.2 GiB. OS eats 15-25 GB. Users see ~95 GB usable.
Mobile Data: How Long Does 5 GB Last?
1 hour Netflix HD = 3 GB. Instagram scroll = 700 MB/hr. Zoom video = 900 MB/hr. Realistic 5 GB month math.
Cloud Storage Billing: GiB vs GB Costs
AWS charges per GB (10⁹). Local file managers show GiB (2³⁰). A '100 GB' bucket showing 93.1 GiB is correct.
Security Footage: terabytes to gigabytes
Convert terabytes to gigabytes for security footage using 1 TB = 1000 GB (decimal). Worked example, quick table, and the mistake that throws results off.
GB vs GiB, MB vs MiB: The 4.9% Storage Discrepancy
1 GB = 10⁹ bytes (SI). 1 GiB = 2³⁰ = 1.074 × 10⁹ bytes (IEC). Drive manufacturers use SI; operating systems mostly show IEC. The 7% gap is why 'my 1 TB drive shows as 931 GB'.
Bits vs Bytes: Marketing Storage Sizes
A 1 TB drive holds 931 GiB of files. Here is why the storage industry uses decimal units while your operating system uses binary, and what that means for you.
Data rate
1 articleData transfer
1 articleData Transfer
1 articleData-transfer
4 articlesDDR4 vs DDR5 Bandwidth: MT/s vs GB/s
DDR4-3200 = 25.6 GB/s per channel. DDR5-5600 = 44.8 GB/s. MT/s ≠ MHz — the doubling is real.
Mbps vs MB/s: Why '100 Mbps' Downloads at 12 MB/s
1 byte = 8 bits, so 100 Mbps ≈ 12.5 MB/s in your browser. Real vs advertised throughput, TCP overhead, and the four places the bits-vs-bytes trap costs you.
HDD vs SATA SSD vs NVMe: MB/s Real Numbers
7200 RPM HDD: 150 MB/s. SATA SSD: 550 MB/s. NVMe Gen4: 7000 MB/s. Bus limits vs media limits.
4K vs 1080p: Bitrates and Storage
1080p HEVC ≈ 8 Mbps. 4K HEVC ≈ 25 Mbps. Netflix caps 4K at 15 Mbps. Compression hides the pixel math.
Density
1 articleDigital image resolution
2 articlesPPI, DPI, and 'Retina': An Honest Look at Screen Density
218 PPI is where a phone stops looking pixelly at arm's length. Beyond 400 you can't see individual pixels no matter how hard you try. Marketing goes far past that.
Screen PPI, DPI and Retina: The Pixel-Density Math That Matters
PPI = √(w² + h²) / diagonal-in-inches. A 27" 4K panel is 163 PPI, a 15.6" 1080p laptop is 141 PPI. Here is when density stops mattering.
Digital-image-resolution
2 articlesCamera Megapixels vs Sensor Size
Megapixels ≠ image quality. Sensor area matters more. iPhone 1/1.28" @ 48 MP vs full-frame 24 MP.
Monitor PPI: 4K 27" vs 1440p 27" vs 5K
PPI = √(w² + h²) / diagonal. 4K 27" = 163 PPI. Retina target = 218 PPI. Text scaling math.
Distance & Speed
1 articleDIY
25 articlesHinge Mortise Depth: Fractional Inches to mm
Hinge mortise depth: cutting a fractional inch spec with a metric router jig. The exact factor, one worked example, and the mistake that quietly skews it.
Router Bit Shanks: Inch to mm Collet Sizing
Router bit shanks: fitting an inch-sized bit into a metric collet. The exact factor, one worked example, and the mistake that quietly skews it.
Sandpaper Grit: FEPA (P-Scale) vs ANSI/CAMI
Sandpaper grit: why a P320 disc isn't the same as ANSI 320. The exact factor, one worked example, and the mistake that quietly skews it.
Paint Coverage: sq ft/Gallon to m²/Liter
Paint coverage: matching a US gallon spec to a metric tin's m²/L rating. The exact factor, one worked example, and the mistake that quietly skews it.
Nail Penny Size: What '10d' Means in mm Diameter
Nail penny size: what the 'd' number actually means in millimeters. The exact factor, one worked example, and the mistake that quietly skews it.
Porch Roof: degrees to percent grade
Convert degrees to percent grade for porch roof using percent grade = tan(degrees) × 100. Worked example, quick table, and the mistake that throws results off.
Drywall Screw Length: Inches to mm at the Hardware Store
Drywall screw length: matching an inch spec to a metric box on the shelf. The exact factor, one worked example, and the mistake that quietly skews it.
Drainage Slope: degrees to percent grade
Convert degrees to percent grade for drainage slope using percent grade = tan(degrees) × 100. Worked example, quick table, and the mistake that throws…
Ramp Build: degrees to percent grade
Convert degrees to percent grade for ramp build using percent grade = tan(degrees) × 100. Worked example, quick table, and the mistake that throws results off.
Shed Roof: degrees to percent grade
Convert degrees to percent grade for shed roof using percent grade = tan(degrees) × 100. Worked example, quick table, and the mistake that throws results off.
Tile Estimate: square feet to square meters
Convert square feet to square meters for tile estimate using 1 ft² = 0.09290304 m². Worked example, quick table, and the mistake that throws results off.
Deck Board Spacing: Fractional Inches to mm Gap
Deck board spacing: setting a metric spacer to a fractional inch gap. The exact factor, one worked example, and the mistake that quietly skews it.
Laser Level Accuracy: mm/m to Percent Grade
Laser level accuracy: what the mm/m spec means as a percent grade. The exact factor, one worked example, and the mistake that quietly skews it.
Garden Shed: square feet to square meters
Convert square feet to square meters for garden shed using 1 ft² = 0.09290304 m². Worked example, quick table, and the mistake that throws results off.
Workshop Layout: square feet to square meters
Convert square feet to square meters for workshop layout using 1 ft² = 0.09290304 m². Worked example, quick table, and the mistake that throws results off.
Woodworking Clamp Pressure: psi to kPa
Woodworking clamp pressure: matching a psi spec to a metric clamp gauge. The exact factor, one worked example, and the mistake that quietly skews it.
Screw Thread Pitch: TPI to mm (It's an Inverse, Not a Multiply)
Screw thread pitch: why TPI to mm needs division, not multiplication. The exact factor, one worked example, and the mistake that quietly skews it.
Garage Wall: square feet to square meters
Convert square feet to square meters for garage wall using 1 ft² = 0.09290304 m². Worked example, quick table, and the mistake that throws results off.
Cabinet Spacer: inches to millimeters
Convert inches to millimeters for cabinet spacer using 1 in = 25.4 mm. Worked example, quick table, and the mistake that throws results off.
Bedroom Floor: square feet to square meters
Convert square feet to square meters for bedroom floor using 1 ft² = 0.09290304 m². Worked example, quick table, and the mistake that throws results off.
Router Depth: inches to millimeters
Convert inches to millimeters for router depth using 1 in = 25.4 mm. Worked example, quick table, and the mistake that throws results off.
Door Trim: inches to millimeters
Convert inches to millimeters for door trim using 1 in = 25.4 mm. Worked example, quick table, and the mistake that throws results off.
Shelf Cleat: inches to millimeters
Convert inches to millimeters for shelf cleat using 1 in = 25.4 mm. Worked example, quick table, and the mistake that throws results off.
Plywood Thickness: inches to millimeters
Convert inches to millimeters for plywood thickness using 1 in = 25.4 mm. Worked example, quick table, and the mistake that throws results off.
Wheelchair Access: degrees to percent grade
Convert degrees to percent grade for wheelchair access using percent grade = tan(degrees) × 100. Worked example, quick table, and the mistake that throws…
Dry volume
1 articleDynamic viscosity
1 articleElectric field strength
1 articleElectric resistivity
1 articleElectrical
15 articlesBattery C-Rate: Converting to Actual Amps for Your Pack
Battery C-rate: what '1C' actually means in amps for your specific pack. The exact factor, one worked example, and the mistake that quietly skews it.
Conduit Fill: How Many AWG Conductors Actually Fit
Conduit fill percentage: why wire count isn't a simple size-for-size swap. The exact factor, one worked example, and the mistake that quietly skews it.
Illuminance: Lux to Footcandles for a Lighting Plan
Illuminance: converting a metric lux target to footcandles for a US lighting plan. The exact factor, one worked example, and the mistake that quietly skews it.
Voltage Drop: Scaling a Per-100ft Rate to Your Actual Run
Voltage drop: scaling a published per-100ft rate to your actual wire run. The exact factor, one worked example, and the mistake that quietly skews it.
Wire Ampacity: Copper vs Aluminum at the Same AWG
Wire ampacity: why the same AWG number carries less current in aluminum. The exact factor, one worked example, and the mistake that quietly skews it.
Solar Panel Watts to Estimated kWh per Day
Solar panel output: turning a wattage rating into a daily kWh estimate. The exact factor, one worked example, and the mistake that quietly skews it.
Inverter Ratings: Continuous Watts to Surge Watts
Inverter sizing: why the surge rating isn't what you can run all day. The exact factor, one worked example, and the mistake that quietly skews it.
Filter Housing: pounds per square inch to kilopascals
Convert pounds per square inch to kilopascals for filter housing using 1 psi = 6.8947572932 kPa. Worked example, quick table, and the mistake that throws…
Arc Flash Incident Energy: cal/cm² to J/cm²
Arc flash incident energy: converting a US cal/cm² rating to metric J/cm². The exact factor, one worked example, and the mistake that quietly skews it.
Compressor Regulator: pounds per square inch to kilopascals
Convert pounds per square inch to kilopascals for compressor regulator using 1 psi = 6.8947572932 kPa. Worked example, quick table, and the mistake that…
LED Lumens to 'Equivalent' Incandescent Watts
LED lumens: what an 'equivalent watts' label on the box actually claims. The exact factor, one worked example, and the mistake that quietly skews it.
Transformer VA to Watts: Factoring in Power Factor
Transformer sizing: why VA and watts aren't the same number. The exact factor, one worked example, and the mistake that quietly skews it.
Hydraulic Press: pounds per square inch to kilopascals
Convert pounds per square inch to kilopascals for hydraulic press using 1 psi = 6.8947572932 kPa. Worked example, quick table, and the mistake that throws…
Water Main: pounds per square inch to kilopascals
Convert pounds per square inch to kilopascals for water main using 1 psi = 6.8947572932 kPa. Worked example, quick table, and the mistake that throws…
Air Line: pounds per square inch to kilopascals
Convert pounds per square inch to kilopascals for air line using 1 psi = 6.8947572932 kPa. Worked example, quick table, and the mistake that throws results off.
Energy
13 articlesDrone Flight Time: Battery Wh, Airline Limits, and the Real Number
A DJI Mini 3 battery is 38 Wh, advertised at 38 min. Real world: 22-28 min. The 100 Wh airline limit means most consumer drones fly under it.
Why Your Home Stove Can't Do Wok Hei, in BTUs
Restaurant wok burners run 100,000–200,000 BTU/h. A good home range tops out around 18,000. Here is what that gap means in kW, and what you can actually do about it.
TOE, BOE and Quads: The Energy Units Governments Actually Report
1 tonne of oil equivalent = 41.868 GJ. 1 barrel of oil equivalent = 6.12 GJ. 1 quad = 1.055 EJ. National energy statistics live in these units, not joules.
EV Range: kWh/100 mi, mi/kWh, MPGe, and Why Winter Halves Your Range
Tesla Model 3 rated 250 Wh/mi = 4.0 mi/kWh = 132 MPGe. But real-world winter driving at −10 °C drops range by 30–40%. Here's the math and physics.
Water Heater: BTU/hr vs kW vs Therms/Month
40,000 BTU/hr = 11.72 kW gas. Electric heater: 4.5 kW. Therms billing: 1 therm = 29.3 kWh. Cost math.
Gasoline vs Diesel Energy Density
Gasoline 34.2 MJ/L. Diesel 38.6 MJ/L (13% more). Explains diesel's better MPG at same displacement.
Calories vs Kilojoules on Food Labels
1 kcal = 4.184 kJ. EU/AU labels use kJ; US uses kcal (labelled 'calories'). Convert your daily intake.
Joule, Calorie, kWh, BTU, eV: One Chart, Every Energy Unit You'll Meet
1 kWh = 3.6 MJ = 860 kcal = 3412 BTU = 2.25 × 10²⁵ eV. Same energy, different disciplines' vocabularies.
Therms and CCF: How Natural Gas Is Billed
US gas utilities bill in therms or CCF. Neither is a familiar unit. Here is what they mean and how to convert to kWh or MJ.
kWh and MWh: Reading an Electric Bill
Your house is billed in kWh. Your factory is billed in MWh. A power plant produces GWh. Here is how the units scale and how to sanity-check a bill.
Electronvolts: The Currency of Atomic Physics
Chemistry uses eV. Nuclear physics uses MeV. Particle physics uses GeV and TeV. Here is what an electronvolt actually is and where each scale fits.
Calories vs Kilocalories: The Food-Label Fudge
A 'calorie' on a US food label is actually a kilocalorie. Here is why nutrition co-opted the unit and how to reconcile it with the joule.
Joules, Calories, kWh, BTU: One Energy, Four Dialects
Utility bills, food labels, thermodynamics texts and HVAC catalogs each use a different energy unit. Here is exactly how they line up, with the calorie fine print no one reads.
Fitness
35 articlesSwim Paddles: Surface Area cm² to in²
Swim paddles: comparing surface area between metric and imperial specs. The exact factor, one worked example, and the mistake that quietly skews it.
Resistance Bands: lb Tension to Newtons
Resistance band tension: what the pound rating means in newtons. The exact factor, one worked example, and the mistake that quietly skews it.
Barbell Plates: Loading kg Plates on an lb Bar
Barbell plates: loading kilogram plates when your bar math is in pounds. The exact factor, one worked example, and the mistake that quietly skews it.
Swim Workout: meters to yards
Convert meters to yards for swim workout using 1 m = 1.0936132983 yd. Worked example, quick table, and the mistake that throws results off.
Treadmill Session: kilometers to miles
Convert kilometers to miles for treadmill session using 1 km = 0.621371192237 mi. Worked example, quick table, and the mistake that throws results off.
Parkrun Route: kilometers to miles
Convert kilometers to miles for parkrun route using 1 km = 0.621371192237 mi. Worked example, quick table, and the mistake that throws results off.
Step Height: centimeters to inches
Convert centimeters to inches for step height using 1 cm = 0.3937007874 in. Worked example, quick table, and the mistake that throws results off.
Sauna Temperature: F to C for a Proper Löyly
Sauna temperature: matching a Finnish löyly session in F and C. The exact factor, one worked example, and the mistake that quietly skews it.
Dumbbell Pair: pounds to kilograms
Convert pounds to kilograms for dumbbell pair using 1 lb = 0.45359237 kg. Worked example, quick table, and the mistake that throws results off.
Mobility Test: centimeters to inches
Convert centimeters to inches for mobility test using 1 cm = 0.3937007874 in. Worked example, quick table, and the mistake that throws results off.
Yoga Mat Thickness: mm to Inches for Travel Mats
Yoga mat thickness: comparing mm specs against an inch-labeled mat. The exact factor, one worked example, and the mistake that quietly skews it.
Deadlift Attempt: pounds to kilograms
Convert pounds to kilograms for deadlift attempt using 1 lb = 0.45359237 kg. Worked example, quick table, and the mistake that throws results off.
High Jump Bar: centimeters to inches
Convert centimeters to inches for high jump bar using 1 cm = 0.3937007874 in. Worked example, quick table, and the mistake that throws results off.
Rowing Erg: kJ Monitor Display to Actual kcal
Rowing erg calories: what the kJ display really means in kcal. The exact factor, one worked example, and the mistake that quietly skews it.
Bodyweight Log: pounds to kilograms
Convert pounds to kilograms for bodyweight log using 1 lb = 0.45359237 kg. Worked example, quick table, and the mistake that throws results off.
Vertical Leap: centimeters to inches
Convert centimeters to inches for vertical leap using 1 cm = 0.3937007874 in. Worked example, quick table, and the mistake that throws results off.
Protein Scoop: Grams to Ounces for Travel Scales
Protein scoop weight: grams to ounces when a travel scale only shows oz. The exact factor, one worked example, and the mistake that quietly skews it.
Kettlebell Plan: pounds to kilograms
Convert pounds to kilograms for kettlebell plan using 1 lb = 0.45359237 kg. Worked example, quick table, and the mistake that throws results off.
Box Jump: centimeters to inches
Convert centimeters to inches for box jump using 1 cm = 0.3937007874 in. Worked example, quick table, and the mistake that throws results off.
Barbell Total: pounds to kilograms
Convert pounds to kilograms for barbell total using 1 lb = 0.45359237 kg. Worked example, quick table, and the mistake that throws results off.
Kettlebell Pood: Converting the Russian Unit to kg/lb
Kettlebell pood: what the old Russian weight unit means in kg and lb. The exact factor, one worked example, and the mistake that quietly skews it.
Hiking Tracker: kilojoules to kilocalories
Convert kilojoules to kilocalories for hiking tracker using 1 kJ = 0.23900573614 kcal. Worked example, quick table, and the mistake that throws results off.
Treadmill Incline: % Grade to Degrees (and Why It Bends)
Treadmill incline: converting % grade to degrees without trusting it past 15%. The exact factor, one worked example, and the mistake that quietly skews it.
Spin Class: kilojoules to kilocalories
Convert kilojoules to kilocalories for spin class using 1 kJ = 0.23900573614 kcal. Worked example, quick table, and the mistake that throws results off.
VO2 Max: mL/kg/min to METs Explained
VO2 max: turning a lab number into METs your cardiologist actually uses. The exact factor, one worked example, and the mistake that quietly skews it.
Nutrition App: kilojoules to kilocalories
Convert kilojoules to kilocalories for nutrition app using 1 kJ = 0.23900573614 kcal. Worked example, quick table, and the mistake that throws results off.
Cycling Computer: kilojoules to kilocalories
Convert kilojoules to kilocalories for cycling computer using 1 kJ = 0.23900573614 kcal. Worked example, quick table, and the mistake that throws results off.
Lap Count: meters to yards
Convert meters to yards for lap count using 1 m = 1.0936132983 yd. Worked example, quick table, and the mistake that throws results off.
Rowing Display: kilojoules to kilocalories
Convert kilojoules to kilocalories for rowing display using 1 kJ = 0.23900573614 kcal. Worked example, quick table, and the mistake that throws results off.
Lifeguard Drill: meters to yards
Convert meters to yards for lifeguard drill using 1 m = 1.0936132983 yd. Worked example, quick table, and the mistake that throws results off.
Charity 5K: kilometers to miles
Convert kilometers to miles for charity 5k using 1 km = 0.621371192237 mi. Worked example, quick table, and the mistake that throws results off.
Triathlon Plan: meters to yards
Convert meters to yards for triathlon plan using 1 m = 1.0936132983 yd. Worked example, quick table, and the mistake that throws results off.
Trail Marker: kilometers to miles
Convert kilometers to miles for trail marker using 1 km = 0.621371192237 mi. Worked example, quick table, and the mistake that throws results off.
Open Water Course: meters to yards
Convert meters to yards for open water course using 1 m = 1.0936132983 yd. Worked example, quick table, and the mistake that throws results off.
Half Marathon Plan: kilometers to miles
Convert kilometers to miles for half marathon plan using 1 km = 0.621371192237 mi. Worked example, quick table, and the mistake that throws results off.
Flow
7 articlesShower Flow Rate: GPM vs LPM Regulations
US federal cap: 2.5 GPM = 9.46 LPM. EU eco-label: 6-9 LPM. Same shower head labelled differently.
VO2 Max: ml/kg/min and MET Equivalents
VO2 max in ml O₂/kg/min. 1 MET = 3.5 ml/kg/min. Convert lab results to daily-activity language.
Volumetric vs Mass vs Molar Flow: Which Rate Does Your Process Actually Care About?
Volumetric flow (m³/h) is what pumps deliver. Mass flow (kg/h) is what heat balances need. Molar flow (kmol/h) is what reactions consume. Pick wrong, get wrong.
CFM, SCFM, ACFM: The Compressed-Air Units That Aren't Interchangeable
ACFM is actual volumetric flow at line conditions; SCFM normalises to standard T and P. At 100 psig, 1 ACFM ≈ 7.8 SCFM.
GPM, LPM, m³/h: The Pump-Curve Trio
1 US gpm = 3.785 L/min = 0.2271 m³/h. Pump curves from US, EU and IEC vendors all use different units on the same graph.
CFM and m³/h: Sizing Ventilation
US HVAC catalogs quote fans in CFM. European catalogs quote in m³/h or L/s. Here is the exact factor and how to size ductwork consistently.
Barrels per Day: The Oil Industry's Flow Unit
OPEC quotes production in million barrels per day. Here is how bbl/d converts to m³/h, litres/second and real refinery throughput.
Fluid permeability
1 articleForce
5 articlesKeyboard Switch Actuation Force in Grams — What 45g Actually Feels Like
Cherry MX Red is 45 g; Black is 60 g. The difference of 15 g sounds tiny but over 8 hours of typing it's the difference between fatigue and comfort.
Kips, Kilonewtons and Tonnes-force: Structural Loads in Three Systems
1 kip = 4.448 kN. 1 tonne-force = 9.807 kN = 2.205 kip. US steel manuals in kips, Eurocode in kN, Latin-American drawings in tf. Same beam, three number systems.
Fishing Line: Pound Test Is Not What You Think It Is
A '10 lb' braid can break a 30 lb bass on light gear. Pound test is a break strength, but diameter is what actually affects casting, visibility and knots.
Dyne vs Newton: CGS vs SI
1 N = 100,000 dyne. Legacy physics texts and older biophysics papers still use dynes. Muscle physiology in dynes/cm².
Newtons, kgf and lbf: Why Weight Is Not Mass
A 100 kg mass weighs 100 kgf on Earth and 16.5 kgf on the Moon. Here is how the kgf and lbf survived alongside the newton, and where the distinction actually matters.
Frequency
12 articlesEvery 10 dB Is Twice as Loud (Roughly)
A whisper is 30 dB, a conversation is 60 dB, a rock concert is 110 dB. That's not linear — 110 dB is billions of times more sound energy than 30 dB. Ears compress it back down.
60, 120, 240 Hz: What You Actually Feel at Each Refresh Rate
The jump from 60 to 120 Hz is huge. 120 to 240 is real but subtle. 240 to 360 is a rounding error for most eyes. A tempo note.
Cents: The Logarithmic Unit That Runs Every Tuner
100 cents = 1 semitone. 1200 cents = 1 octave. Cents are logarithmic because pitch is, and this is why your guitar tuner is not lying about being 3 cents flat.
BPM and Hz: Music Tempo, Heart Rate and the Frequency Bridge
120 BPM = 2 Hz. A 60 Hz mains hum sits at 3600 BPM. Producers, DJs and cardiologists all quote a frequency — divided by 60.
Wavelength vs Frequency vs Photon Energy
λ·f = c. E = hf. Visible 400-700 nm = 430-750 THz = 1.77-3.1 eV. Three ways to describe one photon.
Running Cadence: Steps per Minute
180 spm is the coaching target. Elite runners actually range 170-200. Cadence × stride = pace — the math.
Noise Dose: dBA vs OSHA/NIOSH 8-Hour Limits
OSHA 90 dBA/8 hr. NIOSH 85 dBA/8 hr. Every +3 dB halves safe exposure. Concerts hit 110 dB — 30 s limit.
Heart Rate Zones: %HRmax vs %HRR vs Lactate Threshold
%HRmax and %HRR (Karvonen) give different zone boundaries. Zone 2 at 70% HRmax is not 70% HRR. Full comparison plus LTHR-based zones for serious training.
Audio Frequency Response: 20 Hz - 20 kHz Reality
Human hearing: 20 Hz - 20 kHz theoretical, 40 Hz - 16 kHz typical adult. Speaker specs oversell high end.
Earthquake Magnitude: Richter vs Moment vs Mercalli
Richter M4 → M5 = 10× amplitude, 32× energy. Modern USGS uses Moment magnitude (Mw). Mercalli is felt intensity.
RPM and Hertz: Motor Speeds and Grid Frequency
A 60 Hz motor spins at a different speed than a 50 Hz motor. Here is why grid frequency dictates every industrial motor's RPM and how to convert.
Hertz, Megahertz, Gigahertz: The Radio Spectrum
AM radio is at kHz. FM at MHz. WiFi at GHz. 5G at both. Here is the full spectrum map and what each band is used for.
Fuel economy
1 articleFuel-efficiency-volume
1 articleGarden
10 articlesDrip Irrigation Emitters: GPH to LPH for a Metric System
Drip irrigation emitters: converting GPH ratings to LPH for a metric-labeled kit. The exact factor, one worked example, and the mistake that quietly skews it.
Lawn Mower Deck Width: Inches to cm for a Storage Shed
Lawn mower deck width: checking an inch spec against a metric shed doorway. The exact factor, one worked example, and the mistake that quietly skews it.
Mulch Depth: Inches to cm for a Metric Coverage Calculator
Mulch depth: converting an inch recommendation to cm for a coverage calculator. The exact factor, one worked example, and the mistake that quietly skews it.
Greenhouse Heating: BTU per Square Foot Rule of Thumb
Greenhouse heating load: sizing a heater with the BTU-per-sq-ft rule of thumb. The exact factor, one worked example, and the mistake that quietly skews it.
Soil pH: Why a One-Point Shift Isn't a Small Change
Soil pH: why moving from 6.0 to 5.0 is a 10x change, not a small one. The exact factor, one worked example, and the mistake that quietly skews it.
Compost Delivery: Cubic Yards to Cubic Meters
Compost delivery: converting a US cubic yard order to a metric cubic meter quote. The exact factor, one worked example, and the mistake that quietly skews it.
Seed Spacing: Inches to cm for an Imported Seed Packet
Seed spacing: converting an inch spacing guide to cm for a metric seed packet. The exact factor, one worked example, and the mistake that quietly skews it.
Rainfall: Weekly Inches to mm for Irrigation Planning
Weekly rainfall: converting an inch total to mm for a metric irrigation controller. The exact factor, one worked example, and the mistake that quietly skews it.
Fertilizer NPK: Percentage to Actual Pounds of Nutrient
Fertilizer NPK ratio: turning the percentage on the bag into real pounds of nutrient. The exact factor, one worked example, and the mistake that quietly skews…
Soil Amendment Rate: lb/acre to kg/ha
Soil amendment application rate: converting a US lb/acre spec to metric kg/ha. The exact factor, one worked example, and the mistake that quietly skews it.
Health
10 articlesHearing Thresholds: dB HL to dB SPL by Frequency
Hearing thresholds: why the dB HL to dB SPL offset changes with frequency. The exact factor, one worked example, and the mistake that quietly skews it.
Peak Flow Meter: L/min to Percent of Personal Best
Peak flow readings: converting L/min to the percent-of-personal-best asthma zones. The exact factor, one worked example, and the mistake that quietly skews it.
Forehead vs Oral Thermometer: The Typical Offset
Forehead thermometers: why the reading runs lower than an oral one, and by how much. The exact factor, one worked example, and the mistake that quietly skews…
Infant Growth Charts: kg to lb Across International Charts
Infant growth percentiles: converting kg chart values to lb for family back home. The exact factor, one worked example, and the mistake that quietly skews it.
Vitamin D Lab Results: ng/mL to nmol/L
Vitamin D results: converting ng/mL to nmol/L across different lab reports. The exact factor, one worked example, and the mistake that quietly skews it.
Pediatric Medication Dosing: mg/kg to a Daily mg Total
Pediatric dosing: converting a standard mg/kg rate to an actual daily total. The exact factor, one worked example, and the mistake that quietly skews it.
Skinfold Calipers: mm Measurements to Body Fat %
Skinfold calipers: why mm measurements need a regression equation, not a factor. The exact factor, one worked example, and the mistake that quietly skews it.
BMI: The Imperial Formula's Hidden 703 Constant
BMI calculation: where the imperial formula's '703' constant actually comes from. The exact factor, one worked example, and the mistake that quietly skews it.
Pulse Oximeter SpO2: Adjusting Expectations for Altitude
Pulse oximeter readings: why a 'normal' SpO2 shifts at altitude. The exact factor, one worked example, and the mistake that quietly skews it.
A1C Percentage to Average Glucose in mg/dL
A1C to average glucose: the clinical formula behind the eAG number. The exact factor, one worked example, and the mistake that quietly skews it.
Heat flux density
1 articleHeat transfer coefficient
1 articleHVAC
25 articlesRefrigerant Charge: Ounces to Grams for a Metric Scale
Refrigerant charging: converting an ounce charge spec to grams on a digital scale. The exact factor, one worked example, and the mistake that quietly skews it.
Duct Static Pressure: in w.c. to Pascals
Duct static pressure: converting in w.c. readings to Pascals for a metric manometer. The exact factor, one worked example, and the mistake that quietly skews…
Heat Pump: BTU per hour to kilowatts
Convert BTU per hour to kilowatts for heat pump using 1 BTU/h = 0.00029307107017 kW. Worked example, quick table, and the mistake that throws results off.
Heat Pump COP to HSPF: A Rule-of-Thumb Bridge
Heat pump efficiency: converting a COP figure to an HSPF-style rating. The exact factor, one worked example, and the mistake that quietly skews it.
Tankless Heater: US gallons per minute to liters per minute
Convert US gallons per minute to liters per minute for tankless heater using 1 US GPM = 3.785411784 L/min. Worked example, quick table, and the mistake that…
Mini Split: BTU per hour to kilowatts
Convert BTU per hour to kilowatts for mini split using 1 BTU/h = 0.00029307107017 kW. Worked example, quick table, and the mistake that throws results off.
Sump Pump: US gallons per minute to liters per minute
Convert US gallons per minute to liters per minute for sump pump using 1 US GPM = 3.785411784 L/min. Worked example, quick table, and the mistake that…
Dew Point vs Relative Humidity: Why There's No Simple Factor
Dew point and relative humidity: two numbers that don't convert with one factor. The exact factor, one worked example, and the mistake that quietly skews it.
Furnace Blower: cubic feet per minute to cubic meters per hour
Convert cubic feet per minute to cubic meters per hour for furnace blower using 1 CFM = 1.6990107955 m³/h. Worked example, quick table, and the mistake that…
Boiler Loop: US gallons per minute to liters per minute
Convert US gallons per minute to liters per minute for boiler loop using 1 US GPM = 3.785411784 L/min. Worked example, quick table, and the mistake that…
Duct Velocity: fpm to m/s for a Metric Anemometer
Duct air velocity: converting fpm readings to m/s for a metric tool. The exact factor, one worked example, and the mistake that quietly skews it.
Grow Tent: cubic feet per minute to cubic meters per hour
Convert cubic feet per minute to cubic meters per hour for grow tent using 1 CFM = 1.6990107955 m³/h. Worked example, quick table, and the mistake that…
Thermostat Deadband: °F Interval to °C Interval
Thermostat deadband: converting a temperature interval, not a temperature point. The exact factor, one worked example, and the mistake that quietly skews it.
Irrigation Zone: US gallons per minute to liters per minute
Convert US gallons per minute to liters per minute for irrigation zone using 1 US GPM = 3.785411784 L/min. Worked example, quick table, and the mistake that…
Shop Exhaust: cubic feet per minute to cubic meters per hour
Convert cubic feet per minute to cubic meters per hour for shop exhaust using 1 CFM = 1.6990107955 m³/h. Worked example, quick table, and the mistake that…
Shower Valve: US gallons per minute to liters per minute
Convert US gallons per minute to liters per minute for shower valve using 1 US GPM = 3.785411784 L/min. Worked example, quick table, and the mistake that…
Furnace BTU: Input Rating to Output Using AFUE%
Furnace BTU output: what the nameplate input rating actually delivers. The exact factor, one worked example, and the mistake that quietly skews it.
Range Hood: cubic feet per minute to cubic meters per hour
Convert cubic feet per minute to cubic meters per hour for range hood using 1 CFM = 1.6990107955 m³/h. Worked example, quick table, and the mistake that…
Humidity Ratio: Grains per Pound to Grams per Kilogram
Humidity ratio: converting grains per pound to the metric g/kg standard. The exact factor, one worked example, and the mistake that quietly skews it.
Bathroom Fan: cubic feet per minute to cubic meters per hour
Convert cubic feet per minute to cubic meters per hour for bathroom fan using 1 CFM = 1.6990107955 m³/h. Worked example, quick table, and the mistake that…
Airflow Sizing: CFM per Ton of Cooling
Airflow sizing: the 400 CFM-per-ton rule and when it doesn't apply. The exact factor, one worked example, and the mistake that quietly skews it.
SEER to EER: A Rule-of-Thumb Efficiency Conversion
SEER to EER: the rough conversion HVAC shoppers actually use. The exact factor, one worked example, and the mistake that quietly skews it.
Window Unit: BTU per hour to kilowatts
Convert BTU per hour to kilowatts for window unit using 1 BTU/h = 0.00029307107017 kW. Worked example, quick table, and the mistake that throws results off.
Server Room: BTU per hour to kilowatts
Convert BTU per hour to kilowatts for server room using 1 BTU/h = 0.00029307107017 kW. Worked example, quick table, and the mistake that throws results off.
Garage Heater: BTU per hour to kilowatts
Convert BTU per hour to kilowatts for garage heater using 1 BTU/h = 0.00029307107017 kW. Worked example, quick table, and the mistake that throws results off.
Illumination
4 articlesLumens, Not Watts: Shopping for LEDs Without Getting Fooled
800 lumens is a 60 W incandescent. Wattage is what a bulb draws, not how bright it is. Once you learn one number, hardware store shopping stops being a lottery.
Camera Exposure Stops: Aperture, Shutter, ISO — the EV Equation
One stop = 2× light. f/2.8 → f/4 halves light; ISO 100 → 200 doubles gain. The EV formula ties aperture, shutter and ISO into one number.
Lumens vs Lux vs Candela: Bulbs, Rooms, Torches
Lumens = total output. Lux = lm/m² at a surface. Candela = directional intensity. Three different questions.
Lux and Foot-Candles: Lighting Design
US lighting codes quote foot-candles. Everywhere else quotes lux. Here is the exact factor and how to hit an IES-recommended illuminance in either.
Inductance
1 articleIndustrial
10 articlesPallet Rack Beam Capacity: kg to lb for a US Warehouse
Pallet rack beam capacity: converting a kg rating to lb for a US safety inspection. The exact factor, one worked example, and the mistake that quietly skews it.
Pipe Schedule Wall Thickness: Inches to mm for a Metric Weld Spec
Pipe schedule wall thickness: converting a Schedule 40 spec to mm for welding. The exact factor, one worked example, and the mistake that quietly skews it.
Load Cell Sensitivity: mV/V Output to kg for a Specific Cell
Load cell output: converting a mV reading to kg for a specific sensitivity and excitation. The exact factor, one worked example, and the mistake that quietly…
Conveyor Belt Speed: fpm to m/s for Imported Equipment
Conveyor belt speed: converting fpm to m/s to match an imported drive controller. The exact factor, one worked example, and the mistake that quietly skews it.
Bearing Bore Size: mm to Inches for a Legacy Shaft
Bearing bore size: matching a metric bearing to an inch-machined legacy shaft. The exact factor, one worked example, and the mistake that quietly skews it.
3D Printer Nozzle: mm Diameter to Inches for a US Spec Sheet
3D printer nozzle diameter: converting the standard mm sizes to inches. The exact factor, one worked example, and the mistake that quietly skews it.
Workplace Noise: dBA to Permissible Exposure Time
Workplace noise exposure: why 5 more dBA cuts your safe exposure time in half. The exact factor, one worked example, and the mistake that quietly skews it.
Industrial Flow Meter: GPM to m³/h for a Metric PLC
Industrial flow rate: converting a GPM sensor reading to m³/h for a metric PLC setpoint. The exact factor, one worked example, and the mistake that quietly…
Gearbox Ratio: Input RPM to Output RPM
Gearbox reduction ratio: converting motor input RPM to actual output RPM. The exact factor, one worked example, and the mistake that quietly skews it.
Compressor Air: SCFM to ACFM at Elevation
Compressed air sizing: correcting SCFM to actual ACFM at your site's elevation. The exact factor, one worked example, and the mistake that quietly skews it.
Kinematic viscosity
1 articleLength
51 articlesOrdering Running Shoes Online — US, UK, and EU Sizes
Running shoe sizes do not convert like clothing. US men's 10 is not EU 43 on every brand. How to use foot length in cm, compare Saucony vs Nike charts, and order half sizes from overseas.
Driveway Markout: yards to meters
Convert yards to meters for driveway markout using 1 yd = 0.9144 m. Worked example, quick table, and the mistake that throws results off.
Ski Length in cm: What the Old Rules Got Wrong
The 'chin-height ski' rule is from the 1980s. Modern shaped skis are typically 5-15 cm shorter than your height, sized to skill and terrain instead.
Guitar String Gauges — Thousandths of an Inch, Pounds of Tension
A '10s' guitar string set has a high E of 0.010 inches. Drop a whole step and tension falls 20%. Gauge and tuning are one system.
Climbing Rope Diameter in mm — Thinner Isn't Always Better
A 9.8 mm rope is a sport climbing standard; 8.5 mm is for alpine and multi-pitch weight savings. But belay devices and grigris care which one you use.
Bicycle Gear Inches — A 19th Century Unit That Refuses to Die
Gear inches = (front teeth / rear teeth) × wheel diameter in inches. It's the diameter of an equivalent penny-farthing wheel, and cyclists still use it in 2026.
Soccer Field: yards to meters
Convert yards to meters for soccer field using 1 yd = 0.9144 m. Worked example, quick table, and the mistake that throws results off.
M6 Is Not '6mm Screw' and #8 Is Not '8mm Anything'
M6 is a 6mm major diameter with a 1.0mm thread pitch. #8 is a 0.164-inch gauge that has nothing to do with 8 anything. Two systems, no overlap.
A Nautical Mile Is One Minute of Latitude, and That Is Not a Coincidence
A nautical mile is 1852 meters — exactly one minute of arc along a meridian. That's why charts have latitude scales you can measure distance on with dividers.
Half an Inch of Headspace, and Add Time Above 1000 Feet
Every canning recipe says 'leave ½ inch headspace and process 10 minutes.' Both numbers change with altitude and with what's in the jar. Here is why.
Bra Sizing Is a Subtraction Problem Nobody Explains
A 34C and a 36B hold almost the same volume. Cup letters are relative to band size, not absolute. Once you know the subtraction, the whole system stops being mystical.
Router Bit Shanks: Why 1/2" Is Worth Buying a Bigger Router For
1/2" shank router bits chatter less, break less, and run truer than 1/4". European 8 mm and 12 mm are the metric equivalents. Here's the honest trade-off.
Why Airliners Cruise at 'Flight Level 350' Instead of 35,000 Feet
FL350 sounds like altitude but isn't. Above 18,000 ft, everyone sets the same altimeter reference and altitude becomes pressure altitude. Here's why.
Lot Listing: acres to square meters
Convert acres to square meters for lot listing using 1 acre = 4046.8564224 m². Worked example, quick table, and the mistake that throws results off.
Yarn Weight: The Knitter's Unit System Nobody Warns You About
Lace, fingering, sport, DK, worsted, aran, bulky, super bulky. Also numbers 0–7. Also WPI (wraps per inch). Three names for the same yarn, and none of them are metric.
Thread Count Is Marketing: What Actually Makes a Sheet Feel Good
1000 thread count sheets are often two 500 counts glued together. Real comfort comes from single-ply cotton at 300-500, plus the weave and yarn size (Ne).
Coffee Grind Sizes in Microns: Notes from a Kitchen Scale and a Ruler
Espresso lives at ~250 µm. Filter at ~600. French press at ~900. Grinders label these as 'fine' or 'medium', which is useless unless you know the scale.
Crop Factor: When a 35 mm Lens Isn't a 35 mm Lens
A 35 mm lens on APS-C acts like ~53 mm on full frame. Micro Four Thirds doubles the number. The 'equivalent' math is a framing conversion, not an optical one.
Why AWG Numbers Go the Wrong Way (And How I Finally Remember)
AWG 10 is fatter than AWG 20. The number counts drawing passes, not thickness. Once that clicks, the whole table stops being weird.
Park Parcel: acres to square meters
Convert acres to square meters for park parcel using 1 acre = 4046.8564224 m². Worked example, quick table, and the mistake that throws results off.
Farm Lease: acres to square meters
Convert acres to square meters for farm lease using 1 acre = 4046.8564224 m². Worked example, quick table, and the mistake that throws results off.
Solar Field: acres to square meters
Convert acres to square meters for solar field using 1 acre = 4046.8564224 m². Worked example, quick table, and the mistake that throws results off.
Horse Paddock: acres to square meters
Convert acres to square meters for horse paddock using 1 acre = 4046.8564224 m². Worked example, quick table, and the mistake that throws results off.
Utility Run: feet to meters
Convert feet to meters for utility run using 1 international foot = 0.3048 m. Worked example, quick table, and the mistake that throws results off.
Tire Sizes: Metric P-Metric vs LT vs Flotation — Reading the Sidewall
P225/45R17 = 225 mm wide, 45% aspect ratio, 17-inch rim. Overall diameter = rim + 2 × (width × aspect). Plus load index, speed rating, and the ±3% rolling-diameter rule.
Building Setback: feet to meters
Convert feet to meters for building setback using 1 international foot = 0.3048 m. Worked example, quick table, and the mistake that throws results off.
Garden Plot: feet to meters
Convert feet to meters for garden plot using 1 international foot = 0.3048 m. Worked example, quick table, and the mistake that throws results off.
Survey Stake: feet to meters
Convert feet to meters for survey stake using 1 international foot = 0.3048 m. Worked example, quick table, and the mistake that throws results off.
Survey Tape: yards to meters
Convert yards to meters for survey tape using 1 yd = 0.9144 m. Worked example, quick table, and the mistake that throws results off.
Fence Line: feet to meters
Convert feet to meters for fence line using 1 international foot = 0.3048 m. Worked example, quick table, and the mistake that throws results off.
Cable Trench: yards to meters
Convert yards to meters for cable trench using 1 yd = 0.9144 m. Worked example, quick table, and the mistake that throws results off.
Landscape Fabric: yards to meters
Convert yards to meters for landscape fabric using 1 yd = 0.9144 m. Worked example, quick table, and the mistake that throws results off.
Swimming: Short Course Meters vs Yards vs Long Course
SCY = 25 yd, SCM = 25 m, LCM = 50 m. World records split by pool type. Times don't convert linearly.
Steps to Kilometres and Miles: Why 10,000 Steps Is Not a Distance
Average stride: 0.76 m (men), 0.67 m (women). 10,000 steps is 6.4 km for a 1.60 m person, 8.4 km for a 1.90 m person — same count, 30% distance gap.
Shoe Sizes: US, UK, EU, Japan — Full Conversion Chart
US 10 = UK 9 = EU 43 = JP 28 for men. Sizes step 8.47 mm (1/3 inch = 1 barleycorn). Full charts + the 1.5-size men-to-women rule.
Lumber: 2x4 Nominal vs 38x89 mm Actual
'2x4' = 1.5" × 3.5" = 38 × 89 mm. Planing loses 1/2" per dimension. Metric-imperial framing math.
Astronomy Distances: AU, Light-Year, Parsec
1 AU = 150 M km. 1 ly = 63,241 AU. 1 pc = 3.26 ly. Solar system uses AU; galactic uses pc.
Hiking Elevation Gain: Cumulative vs Net
Cumulative gain sums every uphill segment. Net = end - start. Trail difficulty depends on cumulative — apps disagree.
Drill Bits: Metric vs Fractional vs Number/Letter Sizes
1/4" = 6.35 mm. Nearest metric: 6 or 6.5 mm. Tap drill charts assume one system — swapping shifts thread engagement.
Clothing Sizes: US vs UK vs EU vs Asian Fits
US 6 = UK 10 = EU 36 = Asian L. Same waist/bust cm mapped to different labels. Online shopping trap.
Brake Disc Thickness: mm vs Thou Wear Limits
New disc 25 mm. Wear limit 23 mm. US thickness gauges read in thou (0.001"). 2 mm = 78.7 thou wear.
Altitude: Feet vs Meters in Aviation and Hiking
Cruising 35,000 ft = 10,668 m. Everest 8848 m = 29,029 ft. Aviation is ft globally; hiking varies.
Nautical Mile vs Statute Mile vs Kilometre: When 'Mile' Isn't 'Mile'
1 nautical mile = 1852 m. 1 statute mile = 1609.344 m. Aviation and marine navigation are in nautical; road signs in statute. Difference: 15%.
Yards and Meters on the Sports Field
American football measures in yards. Track and field measures in metres. Soccer stadiums straddle both. Here is the conversion, and the sport-by-sport reason.
Millimeters and Inches on the Shop Floor
A 0.001-inch tolerance is not a 0.01 mm tolerance. Here is how to convert cleanly between mm and inches without accumulating rounding error on the drawing.
Light-years, Parsecs and Astronomical Units
Astronomers switch units by discipline: AU for planets, parsecs for stars, light-years for the public. Here is how the three scales relate and when each is used.
Kilometers and Miles: What Road Signs Actually Mean
Speed limits, distance markers and odometer readings change units at almost every border. Here is the exact factor, and the mental math that keeps you legal.
Inch Fractions and Decimals: A Reference Chart
A 3/16 drill is 0.1875 in = 4.7625 mm. Here is the full fraction-to-decimal-to-mm table, and why fractional inches survive in modern shops.
Angstroms and Nanometers: Wavelengths and Bond Lengths
Chemists still write bond lengths in ångströms. Physicists write wavelengths in nanometres. Here is why both units survive and how to convert without confusion.
Mils, Microns and Thou: Precision Length in Machining
Thousandths of an inch, micrometres, mils and gauge numbers all describe fractions of a millimetre. Here is how machinists switch between them without losing a decimal.
Meters to Feet — and the US Survey Foot Nobody Talks About
There are two feet in the United States. Confusing them puts survey markers hundreds of feet off across a country. Here is the story.
Lumber volume
1 articleLuminance
1 articleLuminous Intensity
1 articleMagnetic Field Strength
1 articleMagnetic Flux
1 articleMagnetism
5 articlesTesla, Gauss, Millitesla: MRI, Speakers and the Earth's Field
1 T = 10 000 G. Earth's field is 0.5 G; a fridge magnet 50 G; a 3 T MRI is 30 000 G. Same physics, wildly different regimes.
Flux vs Flux Density: Weber, Tesla and When They Are Not the Same
Flux (Wb) is total field through a surface; flux density (T) is field per unit area. 1 T = 1 Wb/m². Confusing them mis-sizes transformer cores.
Nanotesla: The Units of Geomagnetic Surveys and UXO Detection
Earth's field averages 50 000 nT. Buried steel objects cause anomalies of tens to hundreds of nT. Magnetometers read to 0.01 nT.
Amp-Turn, Oersted, A/m: Magnetic Field Strength Units
1 Oe = 79.577 A/m. Amp-turn = current × turns and drives H directly. Coil designers, transformer engineers and NDT technicians all need this table.
Tesla and Gauss: The 10,000-to-1 Split in Magnetism
One tesla equals 10,000 gauss. Simple arithmetic; deep history. How SI and CGS diverged in magnetism and why MRI, geophysics and hard-drive engineering still use different units.
Magnetomotive force
1 articleMarine
15 articlesLife Jacket Buoyancy: Newtons to Pounds of Lift
Life jacket buoyancy: what the newton rating means in pounds of lift. The exact factor, one worked example, and the mistake that quietly skews it.
Kayak Hull Speed: Waterline Length to Knots
Kayak hull speed: why a longer boat isn't proportionally faster. The exact factor, one worked example, and the mistake that quietly skews it.
Marine VHF: Channel Number to Frequency in MHz
Marine VHF channels: why the channel number isn't a simple offset from frequency. The exact factor, one worked example, and the mistake that quietly skews it.
Boat Fuel Tank: US Gallons to Liters for a Range Estimate
Boat fuel tank capacity: converting gallons to liters for a range calculation abroad. The exact factor, one worked example, and the mistake that quietly skews…
Marine Line Diameter: mm to Inches for Deck Hardware
Marine line diameter: matching a metric rope spec to inch-rated deck hardware. The exact factor, one worked example, and the mistake that quietly skews it.
Tide Height: US Feet Charts to Metric Chart Datum
Tide height: converting a US foot-based tide table to a metric chart datum. The exact factor, one worked example, and the mistake that quietly skews it.
Sailboat Displacement: lb to kg for a Metric Spec Sheet
Sailboat displacement: comparing a US pound spec against a European kg listing. The exact factor, one worked example, and the mistake that quietly skews it.
Outboard Motor: Horsepower to Kilowatts for EU Import Rules
Outboard motor power: converting horsepower to kW for import and licensing rules. The exact factor, one worked example, and the mistake that quietly skews it.
Dinghy Race: knots to kilometers per hour
Convert knots to kilometers per hour for dinghy race using 1 knot = 1.852 km/h. Worked example, quick table, and the mistake that throws results off.
Ferry Crossing: knots to kilometers per hour
Convert knots to kilometers per hour for ferry crossing using 1 knot = 1.852 km/h. Worked example, quick table, and the mistake that throws results off.
Depth Sounder: Fathoms to Feet on an Old Chart
Depth sounder readings: converting fathoms on a vintage chart to feet. The exact factor, one worked example, and the mistake that quietly skews it.
Fishing Run: knots to kilometers per hour
Convert knots to kilometers per hour for fishing run using 1 knot = 1.852 km/h. Worked example, quick table, and the mistake that throws results off.
Anchor Chain: Fathoms to Meters for a Scope Calculation
Anchor chain scope: converting a fathom-marked rode to meters. The exact factor, one worked example, and the mistake that quietly skews it.
Sailing Log: knots to kilometers per hour
Convert knots to kilometers per hour for sailing log using 1 knot = 1.852 km/h. Worked example, quick table, and the mistake that throws results off.
Harbor Transit: knots to kilometers per hour
Convert knots to kilometers per hour for harbor transit using 1 knot = 1.852 km/h. Worked example, quick table, and the mistake that throws results off.
Moment-of-inertia
1 articleMusic
10 articlesMIDI Velocity: 0-127 Scale to Actual dB Output
MIDI velocity: why velocity 64 isn't 'half as loud' as velocity 127. The exact factor, one worked example, and the mistake that quietly skews it.
Turntable Pitch Control: Percent Shift to Actual RPM
Turntable pitch control: converting a percent shift to the actual new RPM. The exact factor, one worked example, and the mistake that quietly skews it.
Audio Fader dB: Why -10dB Isn't '10% Quieter'
Audio fader dB: the rule of thumb for perceived loudness, not a linear percent. The exact factor, one worked example, and the mistake that quietly skews it.
BPM to Note Duration: Quarter, Eighth, and Dotted Notes in ms
BPM to milliseconds: setting a delay pedal or DAW grid to match tempo. The exact factor, one worked example, and the mistake that quietly skews it.
Drum Head Tension: Lug Torque to Approximate Pitch
Drum head tuning: why lug torque doesn't map to pitch by a fixed number. The exact factor, one worked example, and the mistake that quietly skews it.
Piano Tuning: Hz Differences to Cents
Piano tuning: converting a Hz difference into the cents a tuner actually reads. The exact factor, one worked example, and the mistake that quietly skews it.
A440 vs A432: The Actual Cents Difference
A440 vs A432: converting the audiophile debate into an actual cents number. The exact factor, one worked example, and the mistake that quietly skews it.
Vinyl Groove Width: Microns to mm for Stylus Matching
Vinyl groove width: converting microns to mm to match the right stylus. The exact factor, one worked example, and the mistake that quietly skews it.
Speaker Impedance: Why Lower Ohms Means More Watts, Not Less
Speaker impedance: why an 4Ω cabinet can draw double the power of an 8Ω one. The exact factor, one worked example, and the mistake that quietly skews it.
Delay Pedal: ms Setting to Tempo-Synced BPM
Delay pedal timing: converting a manual ms knob setting to the song's BPM. The exact factor, one worked example, and the mistake that quietly skews it.
Outdoor
10 articlesSleeping Bag Ratings: EN 13537 Comfort Temp F to C
Sleeping bag temperature ratings: converting the EN 13537 comfort figure to F. The exact factor, one worked example, and the mistake that quietly skews it.
Tent Footprint: sq ft to m² for a Campsite Booking
Tent footprint: converting an American tent spec to m² for a European campsite. The exact factor, one worked example, and the mistake that quietly skews it.
Carabiner Gate Opening: mm to Inches for Rack Compatibility
Carabiner gate opening: converting a mm spec to inches for gear compatibility. The exact factor, one worked example, and the mistake that quietly skews it.
Camp Stove Fuel Canister: Net Grams to Ounces
Camp stove fuel: converting the net gram weight to ounces for a US pack list. The exact factor, one worked example, and the mistake that quietly skews it.
Bear Canister Volume: Liters to Cubic Inches for Permit Rules
Bear canister capacity: converting liters to cubic inches for a permit's minimum size rule. The exact factor, one worked example, and the mistake that quietly…
Trail Mix: Calorie Density per Ounce for Pack Weight Planning
Trail mix calorie density: turning an oz weight into a calorie budget for backpacking. The exact factor, one worked example, and the mistake that quietly…
Compass Bearing: Degrees to NATO Mils
Compass bearings: converting degrees to mils for a military-style compass. The exact factor, one worked example, and the mistake that quietly skews it.
Water Filter Flow Rate: L/min to GPM for a Gear Comparison
Backpacking water filter flow rate: converting L/min to GPM for a US comparison chart. The exact factor, one worked example, and the mistake that quietly…
Hiking Elevation Gain: Feet to Meters for an International Trail Guid
Hiking elevation gain: converting a feet-based trail description to meters. The exact factor, one worked example, and the mistake that quietly skews it.
Backpack Volume: Liters to Cubic Inches for a US Comparison
Backpack volume: converting a liter capacity to cubic inches for a US-market comparison. The exact factor, one worked example, and the mistake that quietly…
Parenting
10 articlesBaby Bath Water: Safe Temperature in F and C
Baby bath water temperature: hitting the safe range on either scale. The exact factor, one worked example, and the mistake that quietly skews it.
Medicine Dropper: mL to Teaspoons for a Kids' Dosage
Kids' medicine dosing: converting a mL dropper reading to teaspoons safely. The exact factor, one worked example, and the mistake that quietly skews it.
Growth Chart Height: WHO cm to Inches for Family Updates
Growth chart height: converting WHO cm measurements to inches for relatives. The exact factor, one worked example, and the mistake that quietly skews it.
Stroller Weight Capacity: lb to kg for an Imported Model
Stroller seat weight limit: converting a US lb rating for a metric-only imported model. The exact factor, one worked example, and the mistake that quietly…
Kids' Shoe Sizes: US to EU, and Why the Jump Isn't Even
Children's shoe sizes: why US and EU scales don't line up with a simple offset. The exact factor, one worked example, and the mistake that quietly skews it.
Crib Mattress Size: EU cm Standard to US Inches
Crib mattress sizing: why EU and US standards aren't just unit conversions of each other. The exact factor, one worked example, and the mistake that quietly…
Baby Food Jars: oz Sizes to Grams for a Metric Recipe
Baby food jar sizes: converting an oz jar spec to grams for a homemade batch. The exact factor, one worked example, and the mistake that quietly skews it.
Car Seat Weight Limits: lb to kg for an Imported Seat
Car seat weight limits: converting a US lb rating to kg for an imported seat's manual. The exact factor, one worked example, and the mistake that quietly…
Diaper Sizing: kg Weight Charts to lb for US Shoppers
Diaper sizing: converting a kg weight chart to the lb range on a US package. The exact factor, one worked example, and the mistake that quietly skews it.
Baby Formula Scoop: Brand-Specific Grams to mL
Baby formula scoops: why one brand's scoop doesn't match another's mL mark. The exact factor, one worked example, and the mistake that quietly skews it.
Percentage
1 articlePermeability
1 articlePhotography
10 articlesISO Sensitivity: Why Each Stop Doubles, Not Adds
ISO sensitivity: understanding the doubling scale behind 100, 200, 400.... The exact factor, one worked example, and the mistake that quietly skews it.
f-stop to T-stop: Why There's No Universal Conversion
f-stop vs T-stop: why the same aperture number means different actual light on different lenses. The exact factor, one worked example, and the mistake that…
ND Filters: Stops to Shutter Speed Multiplier
ND filters: converting a stop rating into the actual shutter time multiplier. The exact factor, one worked example, and the mistake that quietly skews it.
Tripod Load Capacity: kg to lb for a US-Bought Head
Tripod load capacity: matching a kg-rated tripod to a lb-rated head. The exact factor, one worked example, and the mistake that quietly skews it.
Megapixels to Maximum Print Size at 300 DPI
Megapixels: what your camera's resolution actually supports for print size. The exact factor, one worked example, and the mistake that quietly skews it.
Color Temperature: Kelvin to Mired for Gel Selection
Color temperature: why lighting gels are rated in mired, not Kelvin directly. The exact factor, one worked example, and the mistake that quietly skews it.
Mirrorless Camera Battery: mAh to Wh for Airline Rules
Mirrorless camera battery: converting mAh to Wh for airline carry-on limits. The exact factor, one worked example, and the mistake that quietly skews it.
Print Sizes: Inches to cm (8x10, 5x7, and Friends)
Print sizes: converting the classic American inch sizes to cm for a European lab. The exact factor, one worked example, and the mistake that quietly skews it.
Flash Guide Number: Feet to Meters
Flash guide number: converting a feet-rated GN to meters for a metric manual. The exact factor, one worked example, and the mistake that quietly skews it.
Shutter Speed: Fractions to Decimal Seconds
Shutter speed fractions: converting 1/250 and friends to decimal seconds. The exact factor, one worked example, and the mistake that quietly skews it.
Power
16 articlesSolar Inverter kW vs Panel kW: Why They Don't Match
A 10 kW panel array often pairs with a 7.6 kW inverter. This is not a mistake — panels rarely hit nameplate, and 'DC/AC ratio' 1.2-1.3 is optimal.
E-Bike Motor Ratings: Watts, Newton-Meters, and the Legal Limit
A 250 W EU-legal e-bike can produce 90 Nm of torque, more than a 750 W US e-bike with less peak power. Watts and Nm measure different things.
12,000 BTU Is One Ton Is 3.5 kW: The AC Sizing Rosetta
Air conditioners are sold in BTU/hr in North America, in 'tons' by HVAC pros, and in kW in Europe. All three describe the same thing. Here is the honest sizing guide.
Car Horsepower: hp, PS, kW, and BHP — Why 300 PS ≠ 300 hp
1 mechanical hp = 0.7457 kW. 1 PS (metric) = 0.7355 kW — a 1.4% gap. Plus SAE net vs DIN vs ECE R85: why the same engine gets three different rating numbers.
USB-C Power Delivery: Watts, Volts, Amps and the PD 3.1 Extended Range
USB-C PD tops out at 240 W (48 V × 5 A) since PD 3.1 EPR. Here is every voltage/current combo, the cable-marking rules, and why your laptop charges slowly.
Wind Turbine: Nameplate MW vs Capacity Factor
2 MW turbine × 30% capacity factor = 5256 MWh/yr. Nameplate rating vs real output — the 3× gap.
Solar Panels: W per m² vs Peak Sun Hours
Modern panels 200 W/m². Peak sun hours 4-6/day. 400 W panel × 5 PSH = 2 kWh/day. Real yield math.
Cycling Watts per Kilogram: Power-to-Weight
W/kg is the universal fitness marker. 4 W/kg = strong amateur; 6 W/kg = pro. Convert lb-based numbers.
EV Charging Speed: kW vs Miles per Hour Added
150 kW DC fast = 600 mi/hr added to a Model 3. Level 2 at 11 kW = 30 mi/hr. AC vs DC — different math.
Air Conditioner Sizing: BTU/hr vs Tons vs kW
1 ton AC = 12,000 BTU/hr = 3.517 kW. A '3-ton unit' = 36,000 BTU/hr — sized to about 1500 sq ft.
Watt, Horsepower, BTU/h, Ton: The Power Units of HVAC and Motors
1 hp = 746 W. 1 ton refrigeration = 12 000 BTU/h = 3.517 kW. Same physical quantity, four different sales sheets.
Horsepower Variants: Mechanical, Metric, Electrical, Boiler
1 hp (mechanical) = 745.7 W. 1 PS = 735.5 W. 1 electrical hp = 746 W. 1 boiler hp = 9810 W. Four horsepowers, four numbers.
dBi, dBd, dBm: RF Gain and Power Units
0 dBd = 2.15 dBi. 0 dBm = 1 mW = −30 dBW. Link budgets live on these dB conversions — miss one, misplace an antenna.
dBA, dBC, dBZ: The Weighted Sound Levels That Aren't Interchangeable
dBA weights for human ear response. dBC is flatter, keeps low frequencies. dBZ is unweighted. 90 dBA in a factory can be 100 dBC — same sound, different exposure limit.
dBm and Milliwatts: RF Power the Log Way
Radio engineers speak in dBm. A 20 dBm signal is 100 mW. Here is the log math and why every WiFi and cellular signal ends up expressed this way.
HP vs kW vs PS: Three Horsepowers, One Engine
Metric, mechanical, electrical, brake — there are at least four "horsepowers" and they disagree by up to 1.4%. Here is which one your car brochure is quoting.
Pressure
23 articlesPressure Cooker PSI at Altitude — Your High-Setting Isn't 15 PSI
A '15 psi' pressure cooker is 15 psi gauge (above ambient). At 2000 m altitude, ambient is lower so cooking temperature drops even at the same gauge reading.
Bike Tire PSI Isn't One Number — It's a Weight Calculation
The number molded into your tire is a maximum, not a target. Real pressure depends on your weight, the tire width, and whether you have tubes.
Bike Shock: pounds per square inch to bar
Convert pounds per square inch to bar for bike shock using 1 psi = 0.068947572931 bar. Worked example, quick table, and the mistake that throws results off.
Why Blood Pressure Is Still Measured in Millimeters of Mercury
The reason your doctor says '120 over 80' is that a mercury column that tall balances the pressure. It's an antique unit that refuses to die because it just works.
Tire Pressure: Why the Sticker Says 'Cold' and Why It Matters
32 psi cold is 34 psi after ten miles. The door-jamb sticker means cold. Ignore that and you'll chase a pressure that doesn't exist.
Pressure Washer: pounds per square inch to bar
Convert pounds per square inch to bar for pressure washer using 1 psi = 0.068947572931 bar. Worked example, quick table, and the mistake that throws results…
Air Tank: pounds per square inch to bar
Convert pounds per square inch to bar for air tank using 1 psi = 0.068947572931 bar. Worked example, quick table, and the mistake that throws results off.
Espresso Machine: pounds per square inch to bar
Convert pounds per square inch to bar for espresso machine using 1 psi = 0.068947572931 bar. Worked example, quick table, and the mistake that throws…
Paint Sprayer: pounds per square inch to bar
Convert pounds per square inch to bar for paint sprayer using 1 psi = 0.068947572931 bar. Worked example, quick table, and the mistake that throws results off.
Tire Pressure: PSI, Bar, kPa on Door Placards Worldwide
32 psi = 2.21 bar = 221 kPa — same inflation, three number systems. Cold vs hot pressure, TPMS thresholds, and the +4 psi towing rule.
Scuba Diving: Depth in Meters/Feet vs Bar Pressure
Every 10 m of seawater adds 1 bar. 30 m dive = 4 bar absolute. Nitrogen loading tables scale with pressure, not depth.
Blood Pressure: mmHg vs kPa Around the World
120/80 mmHg = 16/10.7 kPa. Some EU countries chart in kPa. Same hypertension threshold, different numbers.
Aircraft Cabin Pressure: 8000 ft Altitude Effect
Cruise cabin = 8000 ft equivalent = 75.3 kPa = 10.9 psi. 25% less oxygen than sea level — jet lag physiology.
inH₂O, mmH₂O, cmH₂O: Water Column Pressure for Low-Delta Systems
1 inH₂O ≈ 249 Pa. HVAC static pressure, CPAP therapy and manometers all live in the 0.1–10 inH₂O range where 'close enough' misses target flows.
Rough to XHV: The Full Vacuum Pressure Ladder
Vacuum spans 15 decades from 1 atm to below 10⁻¹² torr. Each decade needs a different pump. Here is the complete map with torr, mbar and Pa side by side.
Torr, Millitorr, Micron: One Vacuum Unit with Three Names
1 micron = 1 mTorr = 0.001 Torr. HVAC and refrigeration techs pull to 500 microns before charging — that is 0.5 Torr.
Gauge vs Absolute Pressure: psig, psia, barg, bara
Gauge pressure reads zero at atmosphere; absolute reads 14.7 psi. Use absolute for gas-law calcs; use gauge for pipe ratings. Confusing them undercounts moles by 13% at 100 psig.
mmHg, kPa, cmH₂O: The Three Pressure Units Every Clinician Toggles
Arterial pressure in mmHg, CVP in cmH₂O, ventilator settings in cmH₂O or kPa. Sloppy conversions misset PEEP by 40%.
Bar, Barg, Bara, Millibar: The European Pressure Vocabulary
1 bar = 100 kPa = 14.504 psi. 'barg' is gauge, 'bara' absolute, 'mbar' meteorology's favourite. Missing the suffix leaves 1 atm of ambiguity.
Torr and Pascal: The Vacuum Technology Ladder
Vacuum-chamber datasheets span 12 orders of magnitude of pressure. Here is the low-pressure ladder from rough to ultra-high vacuum in torr, mbar and Pa.
Pascals and mmHg: Why Blood Pressure Stayed Old-School
Every medical blood-pressure reading is in mmHg. SI would say kPa. Here is why medicine kept mmHg and how the two convert.
Inches of Mercury: Weather Barometers Explained
US weather reports quote pressure in inHg. Aviation altimeters use it too. Here is how it maps to millibar and hectopascal, and where the differences matter.
Psi vs Bar: Turbo Boost Pressure, Finally Explained
Why turbo boost gauges argue about psi and bar, how the two relate, and the mistake almost every first-time tuner makes about absolute vs gauge pressure.
Radiation
4 articlesUV Index, SPF and MED: How Much Sunscreen Actually Blocks
SPF 30 blocks 96.7% of UVB, SPF 50 blocks 98%. UV Index 8 gives a fair-skinned person sunburn in ~15 min unprotected. Here is how the numbers combine.
Radiation Dose: Flight, CT, Chest X-ray in µSv
Chest X-ray 20 µSv. NYC-LON flight 40 µSv. Abdominal CT 8000 µSv. Background 2400 µSv/yr.
Curie and Becquerel: Radiation Activity Units
The becquerel is one decay per second. The curie is 37 billion. Here is why both units exist and where each is used.
Sievert, Gray, Rem: What Each Radiation Unit Actually Measures
Grays measure absorbed dose. Sieverts weight that dose for biological effect. Becquerels count decays. Here is the distinction — and the safety-critical reason it matters.
Radiation absorbed dose
1 articleRadiation Absorbed Dose
1 articleRadiation activity
1 articleRadiation exposure
1 articleRatio
1 articleResistance
1 articleScience
25 articlesMicropipette Volumes: µL to mL for a Serial Dilution
Micropipette volumes: converting microliter draws into the milliliter totals on your protocol. The exact factor, one worked example, and the mistake that…
Centrifuge RCF to RPM: A Radius-Dependent Conversion
Centrifuge speed: why RCF and RPM aren't interchangeable across rotors. The exact factor, one worked example, and the mistake that quietly skews it.
pH Buffer Dilution: Why the Shift Isn't Linear
pH buffer dilution: why cutting concentration in half doesn't shift pH by a fixed amount. The exact factor, one worked example, and the mistake that quietly…
Molarity to ppm: Concentration for a Specific Solute
Molarity to ppm: why the conversion depends on which solute you're using. The exact factor, one worked example, and the mistake that quietly skews it.
Tablet Assay: grams to milligrams
Convert grams to milligrams for tablet assay using 1 g = 1000 mg. Worked example, quick table, and the mistake that throws results off.
Reagent Scale: grams to milligrams
Convert grams to milligrams for reagent scale using 1 g = 1000 mg. Worked example, quick table, and the mistake that throws results off.
Soil Sample: grams to milligrams
Convert grams to milligrams for soil sample using 1 g = 1000 mg. Worked example, quick table, and the mistake that throws results off.
Specific Gravity to Density: Applying the Water Reference
Specific gravity to density: what the dimensionless number actually means in kg/m³. The exact factor, one worked example, and the mistake that quietly skews it.
Buffer Recipe: grams to milligrams
Convert grams to milligrams for buffer recipe using 1 g = 1000 mg. Worked example, quick table, and the mistake that throws results off.
Kelvin to Celsius: The Offset That's Easy to Forget
Kelvin to Celsius: why it's a pure offset, not a scaling factor. The exact factor, one worked example, and the mistake that quietly skews it.
Solar Cell: joules to electronvolts
Convert joules to electronvolts for solar cell using 1 J = 6.241509074e18 eV. Worked example, quick table, and the mistake that throws results off.
Density: g/cm³ to kg/m³ for Lab Reports
Density conversion: g/cm³ to the kg/m³ your lab report template expects. The exact factor, one worked example, and the mistake that quietly skews it.
Chemistry Lecture: joules to electronvolts
Convert joules to electronvolts for chemistry lecture using 1 J = 6.241509074e18 eV. Worked example, quick table, and the mistake that throws results off.
Light Wavelength: nm to Frequency in Hz
Wavelength to frequency: why it's an inverse relationship, not a multiply. The exact factor, one worked example, and the mistake that quietly skews it.
Particle Detector: joules to electronvolts
Convert joules to electronvolts for particle detector using 1 J = 6.241509074e18 eV. Worked example, quick table, and the mistake that throws results off.
TLC Chromatography: Rf Value to Distance Traveled
Thin-layer chromatography: turning an Rf value back into a spot's actual distance. The exact factor, one worked example, and the mistake that quietly skews it.
Semiconductor Bandgap: joules to electronvolts
Convert joules to electronvolts for semiconductor bandgap using 1 J = 6.241509074e18 eV. Worked example, quick table, and the mistake that throws results off.
Cell Culture Confluency: Percent to an Estimated Cell Count
Cell culture confluency: turning a percentage into an estimated cell count for a specific flask. The exact factor, one worked example, and the mistake that…
Atomic Physics: joules to electronvolts
Convert joules to electronvolts for atomic physics using 1 J = 6.241509074e18 eV. Worked example, quick table, and the mistake that throws results off.
LED Datasheet: nanometers to angstroms
Convert nanometers to angstroms for led datasheet using 1 nm = 10 Å. Worked example, quick table, and the mistake that throws results off.
Photon Lab: nanometers to angstroms
Convert nanometers to angstroms for photon lab using 1 nm = 10 Å. Worked example, quick table, and the mistake that throws results off.
Microscope Filter: nanometers to angstroms
Convert nanometers to angstroms for microscope filter using 1 nm = 10 Å. Worked example, quick table, and the mistake that throws results off.
Spectroscopy Line: nanometers to angstroms
Convert nanometers to angstroms for spectroscopy line using 1 nm = 10 Å. Worked example, quick table, and the mistake that throws results off.
Laser Diode: nanometers to angstroms
Convert nanometers to angstroms for laser diode using 1 nm = 10 Å. Worked example, quick table, and the mistake that throws results off.
Plant Extract: grams to milligrams
Convert grams to milligrams for plant extract using 1 g = 1000 mg. Worked example, quick table, and the mistake that throws results off.
Sensitivity
1 articleSolution concentration
4 articlesOsmolarity vs Osmolality: Why IV Fluids Come With Both
Osmolarity: osmoles per litre of solution. Osmolality: osmoles per kg of water. Plasma is 285–295 mOsm/kg. Confuse the units and IV fluid causes cell damage.
Molarity, Molality, Normality: Solution Concentration Units
Molarity (mol/L) uses solution volume. Molality (mol/kg) uses solvent mass. Normality is molarity × valence. Miss the difference and titrations fail.
mg/dL vs mmol/L: Glucose, Cholesterol and the US–EU Divide
Glucose 100 mg/dL = 5.55 mmol/L. Cholesterol 200 mg/dL = 5.18 mmol/L. The conversion factor is different for every analyte — it depends on molecular weight.
IU vs mg: International Units for Vitamins, Hormones and Enzymes
1 IU vitamin D = 0.025 µg. 1 IU vitamin E = 0.67 mg (natural) or 0.91 mg (synthetic). IU is a bioactivity unit; the mg equivalent depends on the specific compound.
Sound Level
1 articleSpecific heat capacity
1 articleSpeed
6 articlesBeaufort Force 6 Is Where I Stop Sailing
The Beaufort scale was invented so sailors could describe wind without instruments. It still works. Force 4 is 'small waves'. Force 8 is 'stay home'.
Running Pace: Converting Between Min/km and Min/mile Without Doing Math Mid-Run
5:00/km is 8:03/mile. A sub-4-hour marathon is 5:41/km or 9:09/mile. Memorise five reference paces and you'll never need a converter mid-run.
Wind Speed: mph, kph, knots, m/s, and the Beaufort Scale
1 knot = 1.852 km/h = 1.15078 mph = 0.5144 m/s. Beaufort scale runs 0–12 by v^1.5. Gusts vs sustained: WMO uses 10-min average, US uses 2-min.
Running Pace: min/km vs min/mile — Full Conversion Table
5:00/km = 8:03/mile. Convert training pace, race splits and marathon targets between km and mile with the exact 1.609344 factor.
Mach Number: Not a Speed, But a Ratio
Mach 1 at sea level is 340 m/s. Mach 1 at 40,000 ft is 295 m/s. Here is why a Mach number is not a constant speed and how to convert it.
The Beaufort Wind Scale in mph, km/h and knots
Beaufort 8 is 'gale force'. But what is that in knots or km/h? Here is the full 0–12 scale with modern-unit equivalents.
Sports
10 articlesDisc Golf: Disc Weight Grams to Ounces
Disc golf disc weight: converting a grams spec for a US scale check. The exact factor, one worked example, and the mistake that quietly skews it.
Tennis Racquet String Tension: lb to kg for a Stringer
Tennis string tension: converting a US pound spec for a metric stringing machine. The exact factor, one worked example, and the mistake that quietly skews it.
Snowboard Length: cm to Inches for a US Size Chart
Snowboard length: converting a metric spec into the inches a US sizing chart uses. The exact factor, one worked example, and the mistake that quietly skews it.
Ski Boot Mondopoint: Why It Isn't a Simple Formula
Ski boot Mondopoint sizing: why brand charts don't agree on a formula. The exact factor, one worked example, and the mistake that quietly skews it.
Basketball Inflation: PSI to Bar for a European Pump Gauge
Basketball inflation pressure: converting a psi spec to bar on an imported pump gauge. The exact factor, one worked example, and the mistake that quietly…
Water Polo Ball: Circumference cm to Inches by Size
Water polo ball sizing: converting circumference between cm and inches. The exact factor, one worked example, and the mistake that quietly skews it.
Baseball Bat Drop Weight: Length Minus Weight, Not a Ratio
Baseball bat drop weight: why it's a subtraction, not a percentage. The exact factor, one worked example, and the mistake that quietly skews it.
Golf Club Loft: Degrees to a Rule-of-Thumb Distance Change
Golf club loft: why 'more degrees' doesn't subtract a fixed number of yards. The exact factor, one worked example, and the mistake that quietly skews it.
Paintball Hopper Capacity: Ball Count to oz of Paint
Paintball hopper capacity: converting a ball count to actual ounces of paint. The exact factor, one worked example, and the mistake that quietly skews it.
Archery: Draw Length to Recommended Arrow Length
Archery arrow length: why it's draw length plus an offset, not a ratio. The exact factor, one worked example, and the mistake that quietly skews it.
Surface current density
1 articleSurface tension
1 articleTemperature
14 articlesGas Mark 4 Is 350°F: Decoding British Oven Numbers
British recipes call for 'gas mark 6', American ones say 400°F, European ones 200°C. All the same. Here is the cheat sheet I taped inside my cupboard.
Meat Doneness Temperatures: USDA vs Chef's Numbers
USDA says 145°F for beef, 165°F for poultry. Chefs pull at 130°F for medium-rare steak and 155°F for chicken thigh. Here is why both are correct.
Thermostat: Setting °C vs °F Comfort Zones
20°C = 68°F 'cool'. 22°C = 72°F 'warm'. A single °C = 1.8°F — HVAC pros use the 5-9 rule for headroom.
Heat Index: Temperature + Humidity in °F/°C
30°C at 70% RH feels like 35°C. Heat index formulas differ US vs metric — same physiological load.
Oven Temperatures: °C, °F, Gas Mark, and Fan vs Conventional
180°C = 350°F = Gas Mark 4 — but a fan oven at 160°C bakes the same. Full conversion ladder, plus the physics of why fan ovens run cooler.
Candy Stages: Thread, Soft Ball, Hard Crack
Thread 110°C. Soft ball 116°C. Hard crack 149°C. Older recipes list only stage names — modern kitchens need °C or °F.
Air Fryer vs Oven: Temperature and Time Conversion
Air fryer: reduce oven temp by 25°F (14°C), cut time by 20%. The convection math behind the rule.
Wet-Bulb vs Dry-Bulb vs Dew Point: Three Temperatures HVAC Engineers Confuse
Cooling tower approach uses wet-bulb, not ambient. Sizing off dry-bulb oversizes chillers by 15–25%. Here is when to use which.
Thermocouple Millivolt to Temperature: Type K, J, T Conversion Traps
Thermocouples output millivolts, not degrees. A Type K at 500 °C produces 20.64 mV. Skip cold-junction compensation and readings drift by whatever your terminal block reads.
Temperature Interval vs Point: Why 1 °C ≠ 1 °F Ever
A 1 °C interval always equals 1.8 °F, no 32° offset. Confusing intervals with points is the most common HVAC and process-control unit error.
Réaumur, Rømer, Newton: Legacy Temperature Scales in Old Manuals
Antique European instruments and translated 18th-century texts still use Réaumur (0/80), Rømer (7.5/60) and Newton (0/33). Here are the exact conversions.
Absolute vs Relative Temperature: When Kelvin Actually Matters
Ideal gas law, Carnot efficiency and radiative heat transfer only work in absolute temperature. Here is when to switch from Celsius to Kelvin and why the offset silently doubles predicted efficiencies.
Rankine and Kelvin: Absolute Temperature Scales
Kelvin is SI. Rankine is US customary. Both start at absolute zero. Here is why chemical engineers in the US still use Rankine and how to convert.
Celsius vs Fahrenheit: The Delta Trap Nobody Warns You About
Converting 20 °C to Fahrenheit is one formula. Converting a 20 °C temperature rise is a different formula. Here is how to keep them straight.
Thermal conductivity
1 articleThermal expansion
1 articleThermal-resistance
1 articleTime
4 articlesSwim Splits: 500m to 1000m Pace Predictors
500 free time × 2 + 15 s ≈ 1000 free time. Distance-per-stroke and fatigue arc make the doubling non-linear.
Sleep Cycles: 90-Minute Blocks and REM Timing
One cycle ≈ 90 min. 5 cycles = 7.5 h. Waking mid-cycle vs between cycles feels different — the math of alarm timing.
Half-Life: Bq, Ci, and Cumulative Dose
N(t) = N₀ · 2^(-t/T½). Tc-99m: T½ = 6 hr. After 24 hr, 6% remains. Nuclear medicine dose scheduling.
Bluetooth Codec Latency: SBC, AAC, aptX, LDAC
SBC ~200 ms. aptX Low Latency ~40 ms. Gaming target <60 ms. Why AirPods lag on Android.
Torque
4 articlesDrill Clutch Numbers Aren't Random: A Torque Primer
The 1–20 collar on a cordless drill sets slip torque. Every number is roughly 3-5 in-lb apart. Once you know what number strips what screw, life gets easier.
Torque: Nm vs lb-ft, and Why Your Wrench Is Probably Miscalibrated
1 N·m = 0.737562 lb·ft. Wheel lugs typically 120–140 N·m (89–103 lb·ft). Click wrenches drift 4% per year — ISO 6789 requires recalibration every 5000 cycles or 12 months.
Nm as Torque vs Nm as Work: Why the Units Look Identical
1 Nm torque and 1 J of work have identical dimensions but different physical meaning. When to use which.
Torque Wrench Units: Nm, lb-ft and kgf·m Without the Guesswork
Your torque spec is in Nm and your wrench is in lb-ft — or vice versa. Here is the exact conversion and the sign of trouble when they disagree.
Travel
20 articlesPassport Photo Size: mm Specs vs the US 2x2 Inch Standard
Passport photo size: matching an mm spec to the US 2x2 inch requirement. The exact factor, one worked example, and the mistake that quietly skews it.
Rental Car Fuel Policy: Liters to Gallons Abroad
Rental car fuel: converting a liter-based fill-up policy to gallons you understand. The exact factor, one worked example, and the mistake that quietly skews it.
Currency Exchange: Mid-Market Rate vs What Your Card Charges
Currency exchange: the mid-market rate isn't the rate you actually get. The exact factor, one worked example, and the mistake that quietly skews it.
Hotel Room Size: m² Listings to ft² for US Guests
Hotel room size: what a '25 m²' European listing means in square feet. The exact factor, one worked example, and the mistake that quietly skews it.
Rail Itinerary: kilometers to miles
Convert kilometers to miles for rail itinerary using 1 km = 0.621371192237 mi. Worked example, quick table, and the mistake that throws results off.
Jet Lag: Time Zone Offset in Hours (Not Always Whole)
Jet lag planning: why some time zone offsets aren't whole hours. The exact factor, one worked example, and the mistake that quietly skews it.
Carry-On Dimensions: cm to Inches Across Airlines
Carry-on dimensions: why 'close enough' cm-to-inch math gets bags gate-checked. The exact factor, one worked example, and the mistake that quietly skews it.
Checked Baggage: Linear Dimensions (L+W+H) cm to Inches
Checked baggage linear limits: converting the L+W+H total, not just one side. The exact factor, one worked example, and the mistake that quietly skews it.
Dual-Voltage Travel Kettle: Watts to Amps at 230V
Dual-voltage travel kettle: why it draws different amps on different grids. The exact factor, one worked example, and the mistake that quietly skews it.
Camera Case: kilograms to pounds
Convert kilograms to pounds for camera case using 1 kg = 2.20462262185 lb. Worked example, quick table, and the mistake that throws results off.
Ski Bag: kilograms to pounds
Convert kilograms to pounds for ski bag using 1 kg = 2.20462262185 lb. Worked example, quick table, and the mistake that throws results off.
Camping Pack: kilograms to pounds
Convert kilograms to pounds for camping pack using 1 kg = 2.20462262185 lb. Worked example, quick table, and the mistake that throws results off.
Cruise Ship Deck Plans: Meters to Feet for Cabin Layout
Cruise ship deck plans: converting the metric scale to feel out your cabin size. The exact factor, one worked example, and the mistake that quietly skews it.
Roaming SIM Data: GB Allowance to MB Actually Used
Roaming SIM data: why your usage tracker shows MB but your plan shows GB. The exact factor, one worked example, and the mistake that quietly skews it.
Checked Bag: kilograms to pounds
Convert kilograms to pounds for checked bag using 1 kg = 2.20462262185 lb. Worked example, quick table, and the mistake that throws results off.
Carry On: kilograms to pounds
Convert kilograms to pounds for carry on using 1 kg = 2.20462262185 lb. Worked example, quick table, and the mistake that throws results off.
Campervan Route: kilometers to miles
Convert kilometers to miles for campervan route using 1 km = 0.621371192237 mi. Worked example, quick table, and the mistake that throws results off.
Border Crossing: kilometers to miles
Convert kilometers to miles for border crossing using 1 km = 0.621371192237 mi. Worked example, quick table, and the mistake that throws results off.
Walking Tour: kilometers to miles
Convert kilometers to miles for walking tour using 1 km = 0.621371192237 mi. Worked example, quick table, and the mistake that throws results off.
Rental Car: kilometers to miles
Convert kilometers to miles for rental car using 1 km = 0.621371192237 mi. Worked example, quick table, and the mistake that throws results off.
Typography
6 articlesPoster Type: typographic points to millimeters
Convert typographic points to millimeters for poster type using 1 PostScript point = 0.3527777778 mm. Worked example, quick table, and the mistake that…
Paper Weight: Why 80 lb Cover Is Not 80 lb Text
GSM is honest: grams per square metre. US pound weights depend on the parent sheet size, so '80 lb text' and '80 lb cover' are wildly different papers.
Sign Shop: typographic points to millimeters
Convert typographic points to millimeters for sign shop using 1 PostScript point = 0.3527777778 mm. Worked example, quick table, and the mistake that throws…
Label Printer: typographic points to millimeters
Convert typographic points to millimeters for label printer using 1 PostScript point = 0.3527777778 mm. Worked example, quick table, and the mistake that…
Laser Engraving: typographic points to millimeters
Convert typographic points to millimeters for laser engraving using 1 PostScript point = 0.3527777778 mm. Worked example, quick table, and the mistake that…
Book Layout: typographic points to millimeters
Convert typographic points to millimeters for book layout using 1 PostScript point = 0.3527777778 mm. Worked example, quick table, and the mistake that…
Velocity-angular
1 articleViscosity
1 articleViscosity Kinematic
1 articleViscosity-kinematic
1 articleVolume
14 articlesBaby Bottles: Ounces, mL, and Why Formula Math Matters
Baby formula is 1 scoop per 2 oz water — the ratio, not the total. Getting concentration wrong is one of the most common feeding errors.
Daily Water Intake: 8 Glasses vs 2 Litres vs Body-Weight Rules
'8×8 oz' = 1.9 L. '2 L' = 67.6 fl oz. 'Half your weight in oz' scales with body mass. Where each rule came from and what the evidence actually supports.
Paint Coverage: L/m² vs Gallons per Square Foot
1 gallon paint ≈ 350 sq ft = 32.5 m². Metric spec: 12 m²/L. Two coats halves that. Real math for a room.
Insulin U-100 vs U-40 vs U-500
U-100 = 100 units per mL. U-500 is 5× stronger. Syringe/pen mismatches are a documented pharmacy-error class.
Engine Displacement: cc vs Litres vs Cubic Inches
1 L = 1000 cc = 61.02 CI. A '5.0 L Mustang' = 5000 cc = 305 CI. Legacy US badges still use CI.
Cocktail Jiggers: 1 oz vs 1.5 oz vs 30 mL vs 45 mL
US jigger = 1.5 fl oz = 44.4 mL. UK 'jigger' = 25 or 35 mL. Home bar recipes assume US convention.
Alcohol Units: UK, US, AU Standard Drinks
UK unit = 10 mL pure ethanol. US = 14 g = 17.7 mL. AU = 10 g = 12.7 mL. Same beer, different unit counts.
US vs UK Fluid Ounces: Why Recipe Conversions Silently Fail
1 US fl oz = 29.57 mL. 1 UK (Imperial) fl oz = 28.41 mL. Close, but pint sizes diverge 20%. Recipes assume one system.
Tablespoons, Teaspoons and Milliliters: Medicine Dosing
A kitchen teaspoon is not a medical teaspoon. Here is why pharmacists insist on millilitre dosing and how the units actually convert.
Liters and Gallons: Fuel Tank Sizing Across Regions
A 15-gallon US tank is not 15 UK gallons. Here is how vehicle fuel-tank capacities convert, and where the US-vs-UK gallon confusion hits hardest.
Cups: US, UK, Metric — Three Sizes
A US cup is 236.6 mL. A metric cup is 250 mL. A UK teacup is 284 mL. Here is why baking recipes cross international lines so badly.
Cubic Yards and Cubic Meters: Ordering Concrete
US ready-mix trucks deliver in cubic yards. European ones deliver in cubic metres. Here is how to specify a slab, foundation, or column without over-ordering.
Barrels: Oil, Beer, and Why They Are Different
An oil barrel is 42 US gallons. A beer barrel is 31 US gallons. A UK beer barrel is 43.2 US gallons. Here is the full disambiguation.
Fluid Ounces: US vs Imperial and the 4% Recipe Error
The US fluid ounce and the Imperial fluid ounce are not the same volume. Here is exactly how far off they are, and why cooking, cocktails and skincare care.
Volumetric Flow
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25 articlesPropane Tanks: Pounds, Gallons, and Why They Don't Match
A '20 lb' BBQ tank holds ~4.7 gallons of liquid propane and 430,000 BTU. Propane sells by weight, buys by gallon, and burns by BTU.
Espresso by Ratio: Why Baristas Weigh Everything
Modern espresso is dose in, yield out, both in grams. A 1:2 ratio at 18 g in / 36 g out is the starting point for most modern coffees.
Feeding a Dog by Cups Is a Bad Idea
One cup of dry dog food can be 90 g or 130 g depending on kibble size. Feed by grams and calories, not cups.
Bowling Ball Weight in Pounds — The 10% Rule Is Nonsense
The old '10% of body weight' rule sends everyone to a 16 lb ball. Modern coaching says pick the heaviest ball you can swing without losing rev rate — often 2-4 lb less.
Archery Draw Weight and Arrow Spine — The Match Nobody Explains
A 50 lb bow with a stiff 340-spine arrow shoots differently than the same bow with a floppy 500-spine arrow. Spine has to match draw weight or the arrow fishtails.
Yeast: Fresh vs Active Dry vs Instant Conversions
1 g instant = 1.25 g active dry = 3 g fresh. Bread recipes rarely specify — here is the exact ratio.
Barbell Plates: kg vs lb Loading
20 kg bar = 44.09 lb. Adding 45 lb plates ≠ 20 kg plates. Gym conversions cost you PRs.
Sugar Weights: Granulated, Brown, Powdered per Cup
1 cup granulated = 200 g. Brown packed = 220 g. Powdered = 120 g. Same volume, wildly different weights.
Salt: Kosher vs Table vs Sea by Volume vs Weight
1 tsp table = 6 g. 1 tsp Diamond Crystal kosher = 3 g. Same 'teaspoon', 2× the sodium. Recipe over-salting root cause.
Protein: g/lb vs g/kg — Fitness Targets Reconciled
0.8 g/lb ≈ 1.76 g/kg. The '1 g per pound of bodyweight' rule doubles the RDA. Full evidence-based targets by goal, and the diminishing-return point.
Baker's Percentage and Bread Hydration
Flour = 100%. Water at 70% hydration = 700 g per 1000 g flour. Levain, salt scale off flour weight.
Flour Weight: Why 1 Cup Is 120–160 g Depending on Scoop
1 cup of all-purpose flour weighs 120 g spooned or 160 g scooped. Recipe failures traced to volume vs weight. Full weight table for wheat, bread, cake, whole-grain, and gluten-free flours.
Egg Sizes: US Large vs UK Medium vs EU Grades
US large = 57 g. UK medium = 53-63 g. EU large = 63-73 g. Recipes assuming one grade fail on another.
Crypto Denominations: Satoshi, Gwei, Wei
1 BTC = 100,000,000 satoshi. 1 ETH = 10⁹ gwei = 10¹⁸ wei. Micro-transactions and gas math.
Chocolate: % Cacao vs Cocoa Mass vs Cocoa Butter
70% chocolate = 70% cocoa solids + cocoa butter total. Fat/solid ratio varies 40/30 or 30/40. Ganache math cares.
Caffeine Content mg: Coffee, Tea, Energy Drinks, Pre-Workout
Espresso 63 mg. Drip 95 mg. Red Bull 80 mg. Pre-workout 200–400 mg. FDA safe cap 400 mg/day. Actual numbers by brand and serving size.
Butter: US Sticks vs Grams vs Cups vs Tablespoons
1 US stick = 113 g = 1/2 cup = 8 tbsp. European butter is sold in 250 g blocks — recipe scaling breaks.
BMI Formula: Metric (kg/m²) vs Imperial (703·lb/in²) — Why the 703 Exists
BMI = kg/m² or 703·lb/in². Same number, two formulas — the 703 absorbs the unit conversion. Plus the four situations where the WHO classification actively misleads.
Baby Weight: kg vs lb-oz Growth Charts
3.4 kg = 7 lb 8 oz. WHO charts use kg; US paediatricians use lb-oz. Percentile bands are unit-agnostic.
Stones: The British Body-Weight Unit That Refuses to Die
British scales still read in stones and pounds. Here is why the stone survived, and how to convert '11 stone 4' to a number that means something abroad.
Metric Tonne, Short Ton, Long Ton: Three Tons
A 100-ton crane rated in the US, UK and EU lifts three different weights. Here is the exact difference between metric, short and long tons.
Grams, Ounces and Troy Ounces in Jewellery
Silver and gold are weighed in troy ounces, which are heavier than kitchen ounces. Here is how a 1 oz gold coin actually weighs 31.1 g, not 28.3 g.
Grains: From Wheat Kernels to Bullet Weights
Bullet weights, arrow-shaft weights and old pharmacy prescriptions are all in grains. Here is the 64.8 mg factor and where it still matters.
Carats vs Karats: Diamonds and Gold Purity
A 2-carat diamond weighs 0.4 g. A 14-karat gold ring is 58.3% pure. Same word, different meaning. Here is the disambiguation.
Why 1 kg is Not Exactly 2.2 lb (and When That Matters)
The 2.2 shortcut is wrong by 0.05%. Here is where that half-a-gram becomes a real problem, from luggage limits to pharmaceutical dosing.