A US cup is about 237 mL, a metric cup is 250 mL and a Japanese cup is 200 mL. The UK has no official cup. The difference matters most in baking.
Also called: metric cup, imperial cup, Australian cup, Canadian cup, Japanese cup
Cup sizes compared
Cup
Volume
Where you’ll see it
US customary cup
236.6 mL
US recipes and measuring cups
US label cup
240 mL
US nutrition labels
Metric cup
250 mL
Australian recipes; Canadian food labels
Japanese cup
200 mL
Japanese recipes
Japanese rice cup
180 mL
Rice cookers and rice recipes
A metric cup holds about 5.7% more than a US cup (250 ÷ 236.6 = 1.057). Over a recipe with 3 cups of flour, that’s 750 mL against 710 mL, a difference of about 40 mL, or nearly 3 US tablespoons.
What about a UK cup?
The cup isn’t one of the units in the UK’s Weights and Measures Act, and British recipes today are usually written in grams and millilitres. If an older or British recipe does say “cup”, check the book’s own conversion notes rather than guessing.
The safer choice
If the recipe gives grams, use them; see weighing flour. If it only gives cups, use a cup set from the same country as the recipe. Spoons differ too; see tablespoon and teaspoon.