US, UK, Metric & Japanese Cups: Why a 'Cup' Isn't Always a Cup
A US cup, a metric cup and a Japanese cup are three different volumes. If you've ever wondered why an imported recipe felt off, this is why.
"One cup" sounds universal. It isn't. Depending on where a recipe was written, a cup can mean anywhere from 200 to 284 millilitres — a difference of more than 40%. For a splash of liquid that's harmless; for the flour in a cake it's the difference between success and a flop.
The four cups you'll meet
| Cup | Volume | Used in |
|---|---|---|
| US customary cup | 240 ml | United States (most recipes) |
| US legal cup | 240 ml | US nutrition labels (officially 240 ml) |
| Metric cup | 250 ml | Australia, NZ, Canada, much of Europe |
| Imperial (UK) cup | 284 ml | Old British recipes (now rare) |
| Japanese cup (gō-based) | 200 ml | Japan, especially rice |
Does the difference matter?
Usually it's small enough to ignore. A US cup (240 ml) and a metric cup (250 ml) differ by about 4% — fine for soups, sauces and most cooking. Where it bites is precise baking and larger quantities: 4% across several cups of flour adds up, and the old imperial cup (284 ml) is nearly 20% bigger than a US cup, which will throw a recipe noticeably.
Modern Britain doesn't use cups
A common point of confusion: although the imperial cup is "the UK cup," British recipes today are written in grams and millilitres, not cups. If you're following a current UK recipe, you're weighing — no cup conversion needed. The 284 ml imperial cup only matters for vintage cookbooks.
Japan: the rice exception
The Japanese cup is 200 ml, and it's tied to the traditional rice measure. The cup that comes with a Japanese rice cooker is this 200 ml size, which is why rice-cooker instructions and Japanese recipes don't line up with a US measuring cup. If a recipe is Japanese, measure rice with the 200 ml cup.
How to convert
To move a recipe between cup standards, convert through millilitres:
- 1 US cup = 240 ml = 0.96 metric cups
- 1 metric cup = 250 ml = 1.04 US cups
- 1 imperial cup = 284 ml = 1.18 US cups
- 1 Japanese cup = 200 ml = 0.83 US cups
For anything beyond a quick estimate, the safest move is to skip cups altogether and weigh the ingredient in grams — then the country of origin stops mattering. See the cup sizes tool for an interactive breakdown, or why grams win for the longer argument.