US Cups vs UK Cups — What's the Difference?

A cup is a cup, right? Not quite. There are actually three different cup sizes used around the world, and using the wrong one can throw off your recipes by up to 20%.

The Three Cup Sizes

Why Are They Different?

The US cup was standardised at 8 US fluid ounces (236.588 ml) in the 19th century as part of the US customary system. The Imperial cup was defined as 10 Imperial fluid ounces (284.131 ml) — and since Imperial and US fluid ounces are themselves different sizes, the cups ended up quite far apart.

The metric cup (250 ml) was adopted by countries that moved to the metric system but wanted to keep the convenience of cup measurements. It's a round number that sits neatly between the US and Imperial cups.

Converting Between Cup Sizes

Do British Recipes Still Use Cups?

Most modern British recipes use grams and millilitres rather than cups. The Imperial cup has largely fallen out of use in the UK. However, when British cooks follow American recipes online, they need to know that those recipes use US cups — and that their UK measuring cups (if they have old ones) are larger.

Our recommendation: Always weigh ingredients when possible. If you must use cups, assume US cups unless the recipe explicitly says otherwise. Pantry Math uses US cups as the standard for all conversions.

Frequently Asked Questions