US cup vs metric cup

The three standards

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Where the odd number comes from

The US cup is not round in millilitres because it was not defined in metric: it is 8 US fluid ounces, and the US fluid ounce is 1/128 of a gallon. Converted, that gives exactly 236.5882365 ml.

The 240 ml legal cup exists precisely to avoid that number: the FDA fixed it round for nutrition labels. Which is why two cups coexist in the same country.

When it matters and when it does not

• It does not matter in stews, soups, sauces and any recipe with tolerance. Six per cent more stock changes nothing.
• It matters in baking, and especially in bread, where the ratio of flour to liquid decides the texture. Six per cent more water in a dough is noticeable while kneading.
• It matters a lot when it accumulates: a recipe with four ingredients measured in cups carries the error four times.

How to tell which your recipe uses

A practical rule that is nearly always right:

• American site or book: US cup, 236.6 ml.
• Australian or New Zealand recipe: metric cup, 250 ml, and a 20 ml tablespoon.
• Modern British recipe: almost always grams and millilitres rather than cups.
• Latin American recipe: usually follows the US cup, though it is worth checking for gram equivalents.

And the spoon changes too

In an Australian recipe the tablespoon is 20 ml instead of 15: 33 % more. It is the largest discrepancy in the whole kitchen measuring system and the one fewest people know about.

Sources and methodology

Weights for solid ingredients come from the King Arthur Baking ingredient weight chart, consulted in September 2026, measured by the spoon-and-level method. Liquids use their documented physical density. Every value and its source is listed in the ingredient table.