US cup vs metric cup

The cup sizes in use

A cup is a volume, but there is more than one cup. The US customary cup is half a US pint, exactly 236.5882365 ml. The US nutrition-labelling cup is defined in US federal regulations as 240 ml. Australia, New Zealand, Canada and several other countries that metricated use a metric cup of 250 ml. The old imperial cup, half an imperial pint, is 284.13 ml and shows up in older British recipes. Details and sources are on the Wikipedia page for the cup, which cites the US Code of Federal Regulations (21 CFR 101.9) for the 240 ml cup.

The tablespoon changes too: the Australian metric tablespoon is 20 ml (4 teaspoons), against 15 ml (3 teaspoons) in the US, UK and most places. A recipe from Australia that says 2 tablespoons of flour means 33% more flour by volume.

What the difference does to the weight

If a recipe is written for one cup and you use another, the ingredient weight changes in proportion to the volume. Using our default weights:

A bake that calls for 3 cups of flour in a US recipe is 360 g; in a metric-cup recipe the same 3 cups is 380 g. That extra 20 g is not a big error for a loaf of bread, but it matters for a delicate sponge or biscuit.

How to tell which cup a recipe means

• If the recipe lists ounces or sticks of butter, it is almost certainly American and the US cup applies.
• If it lists millilitres, grams and “a cup (250 ml)” in its ingredient notes, use 250 ml.
• If it is Australian or from a New Zealand site, assume 250 ml cups and 20 ml tablespoons unless it says otherwise.
• If it is an old UK recipe, check whether “cup” means a teacup; the imperial cup of 284 ml was rarely used by cooks and recipe books often meant a smaller teacup.

When there is still doubt, weigh. All the ingredient pages give grams for the US cup and the 250 ml metric cup, linked from the cups to grams hub.

Frequently asked questions