Free Online Unit Converter — Fast, Accurate & Trusted

Unit conversion looks like a solved problem — every phone, spreadsheet and search box will give you an answer. The problem is that most of them use rounded shortcut factors like 2.2 pounds per kilogram or 3.28 feet per metre. Those numbers are wrong by 0.05% and 0.03% respectively. They are perfect for weighing a suitcase and dangerous for weighing a paediatric drug dose.

Turbo Unit Converter uses the exact conversion factors defined in NIST Special Publication 811, with 12 significant figures kept end-to-end. The result you copy from the tool matches what a calibrated laboratory scale, torque wrench or altimeter would read — not a two-decimal approximation of it. If you are a student checking homework, a mechanic torquing wheel nuts, a nurse dosing by weight, or an engineer converting a European datasheet into US drawing units, the exact factor is the one you want.

Every category on this site is defined by a base unit — metre for length, kilogram for weight, second for time — and each other unit is stored as an exact multiplier against that base. When you convert 12 inches to metres, we do not chain approximations: we look up the exact factor (1 inch = 0.0254 metre by definition), multiply once, and print the result. Where a conversion is non-linear — Celsius to Fahrenheit, dBm to milliwatts — the exact formula is applied rather than a lookup.

Factor sources come from three primary references: the BIPM SI Brochure for the SI unit definitions, NIST SP 811 Appendix B for the extensive US customary and Imperial factor tables, and IEEE/ASTM SI 10 for engineering metric practice. We publish our full methodology and editorial policy so any number on the site can be traced back to a primary source.

Most conversions have a single obvious answer. A handful do not — usually because the same word describes more than one unit. If you are converting fluid ounces, always check whether the recipe or spec sheet is US or Imperial: the US fluid ounce (29.57 mL) is about 4% larger than the Imperial one (28.41 mL), and it is a difference big enough to notice in a cocktail. If you are converting horsepower, check whether the figure is mechanical hp (745.7 W) or metric PS (735.5 W) — European car brochures typically use PS, US ones use hp, and the two disagree by 1.4%.

The other common ambiguity is gauge versus absolute pressure. Boost gauges, tire-pressure gauges and blood-pressure cuffs all read gauge, meaning the difference from ambient atmospheric pressure. MAP sensors, aircraft altimeters and lab instruments read absolute. Comparing a gauge value to an absolute value differs by roughly 1 atmosphere (14.5 psi / 1.013 bar) — which is precisely the boost pressure your street-tuned turbo is trying to make, so mistakes here have consequences.

When in doubt, open the relevant article in our learning centre — each article walks through the units, the exact factors, and one or two worked examples so you can sanity-check any answer.