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.