Side by side
| Measure | US | UK | Australia |
|---|---|---|---|
| Teaspoon | 4.93 mL | 5 mL | 5 mL |
| Tablespoon | 14.79 mL | 15 mL | 20 mL |
| Cup | 236.6 mL | 250 mL metric; 284.1 mL in old recipes | 250 mL |
| Fluid ounce | 29.57 mL | 28.41 mL | not used in recipes |
| Pint | 473.2 mL (16 US fl oz) | 568.3 mL (20 UK fl oz) | not used in current recipes |
| Gallon | 3.785 L | 4.546 L | not used |
US sizes are the exact definitions in NIST Handbook 44. UK pint, gallon and fluid ounce are set by the Weights and Measures Act 1985 (a gallon of 4.54609 litres, a pint of 0.56826125 litres, a fluid ounce of 1/20 pint). The 250 mL metric cup and the Australian 20 mL tablespoon are described in Wikipedia's articles on the cup and the tablespoon, each with its own references.
The three traps
The Australian tablespoon. It holds 20 mL, four teaspoons, against 15 mL elsewhere. Using a US or UK tablespoon for an Australian recipe gives three quarters of the intended amount. That hardly matters for oil or honey, but it changes the result for salt, baking soda and gelatine. The tablespoons to grams converter has an Australian tablespoon option.
The imperial cup. Older British recipes that use cups mean half an imperial pint, 284 mL. That is 1.2 US cups. Read with American cups, such a recipe comes out short by about a sixth on every cup measure.
The pint and the fluid ounce. A UK fluid ounce is slightly smaller than a US one (28.4 mL against 29.6 mL), but a UK pint holds 20 of them against 16 in a US pint. So the UK pint is about 20% bigger, while each UK fluid ounce is about 4% smaller.
Where the sizes don't matter much
The US cup (236.6 mL) and the metric cup (250 mL) differ by about 6%, and the US and metric tablespoons by about 1%. NIST's kitchen guidance says metric cup and spoon measures can often be used interchangeably with US ones. For soups, stews, rice and most cooking, swapping them changes nothing you would notice. For baking, convert the cups to grams and weigh.
US labels use rounder numbers
For nutrition labels only, US rules round the units: a teaspoon is 5 mL, a tablespoon 15 mL, a cup 240 mL and a fluid ounce 30 mL (21 CFR 101.9). This is why a serving that says "1 cup (240 mL)" on a carton is a little more than a measuring cup holds. The difference is 3.4 mL a cup.
Weight is the same everywhere
The ounce and the pound are the same in the US and the UK: 28.35 g and 453.6 g. Grams are grams. Converting a recipe to weight removes every difference in this guide, which is the main argument for weighing.
| Unit | Exact size | Definition | Source |
|---|---|---|---|
| US fluid ounces | 29.5735295625 mL | 1 US fluid ounce = 1/128 US gallon | NIST Handbook 44 (2019) |
| UK | 28.4130625 mL | 1 fluid ounce = 1/20 pint | Weights and Measures Act 1985 |
| US cups | 236.5882365 mL | 1 cup = 8 US fluid ounces = 1/2 liquid pint | NIST Handbook 44 (2019) |
| US legal cups | 240 mL | For US nutrition labels, a cup means 240 mL | 21 CFR 101.9(b)(5)(viii) |
| Metric cups | 250 mL | Metric cup used in Australia, Canada and New Zealand | Wikipedia |
| Imperial cups | 284.130625 mL | Half an imperial pint, the cup in older British recipes | Weights and Measures Act 1985 |
| US pints | 473.176473 mL | 1 liquid pint = 16 US fluid ounces | NIST Handbook 44 (2019) |
| UK | 568.26125 mL | 1 pint = 0.56826125 cubic decimetre | Weights and Measures Act 1985 |
| US gallons | 3785.411784 mL | 1 US gallon = 231 cubic inches = 3.785411784 L | NIST Handbook 44 (2019) |
| UK gallons | 4546.09 mL | 1 gallon = 4.54609 cubic decimetres | Weights and Measures Act 1985 |