The cup — a recipe unit with three different volumes
'One cup of flour' means three different weights of flour depending on which cup — and that is before we get into loose vs sifted.
The cup as a cooking measure was standardised in the US at 8 fl oz in the 1890s. Australia and New Zealand later chose 250 mL for round-number metric convenience. The UK never officially adopted a cup at all — traditional British recipes weigh ingredients instead. Modern recipe apps rarely make the distinction clear.
The exact factors
US legal cup (nutrition labelling) = 240 mL > US customary cup = 236.588 mL = 8 US fl oz > Metric cup (Australia, NZ, Canada) = 250 mL > UK breakfast cup (historic) = 284 mL = 10 UK fl oz > Japanese cup (traditional) = 200 mL
Ingredient-density gotchas
1 US cup of all-purpose flour weighs 120 g if spooned lightly, 140 g if scooped, 160 g if scooped and tapped. That is a 33% spread from measurement technique alone, before any unit conversion. This is why serious baking recipes now list grams — the cup is a rough approximation, not a precise volume.
Worked example — a 3-cup cookie recipe
A US recipe calling for 3 cups of flour = 3 × 236.6 = 710 mL. Followed with a metric measuring cup (3 × 250 = 750 mL), you add 5.6% more flour — enough to make the cookies noticeably drier. Followed with a UK teacup (3 × 284 = 852 mL), you add 20% more flour and the recipe fails.
When cups are OK
Liquid ingredients (water, milk, oil): volume is repeatable, and a 5% error is invisible in most dishes. Chopped vegetables, nuts, herbs: cups are a rough estimate anyway. Salt, spices: switch to teaspoons or grams — cup measurements are wildly inaccurate at small scales.
The five-second recap
US cup = 237 mL. Metric cup = 250 mL. UK cup = 284 mL. For baking, weigh ingredients — cups are approximations.
Try the converters mentioned in this article
FAQ
Which cup is on US nutrition labels?+
The 'US legal cup' = 240 mL, mandated by the FDA. It is 3.4 mL bigger than the traditional 236.6 mL cup.
Do British recipes use cups?+
Rarely. Traditional UK baking uses ounces and grams. Modern UK cookbooks influenced by US authors may use 250 mL metric cups.
What is a 'stick of butter'?+
US convention: 1/2 cup = 4 oz = 113 g. Butter sold outside the US does not come in sticks and this unit does not travel.
This article was written by The Turbo Unit Converter engineering desk (Culinary metrology) and last reviewed on 2026-06-28 against NIST SP 811 and the BIPM SI Brochure. Read our full editorial policy.