How volume conversion works
Every unit in the converter is stored as an exact number of litres, so each conversion is one multiplication and one division:
The tricky part is not the maths but the names. “Cup”, “pint”, “fluid ounce” and “gallon” each mean different amounts in the United States and the United Kingdom, so the converter lists them separately.
US and UK units
US liquid measures come from the US gallon of exactly 231 cubic inches (3.785411784 litres). UK imperial measures come from the imperial gallon, defined in UK law as exactly 4.54609 litres.
| Unit | US | UK (imperial) |
|---|---|---|
| Fluid ounce | 29.5735 ml (1/128 gallon) | 28.4131 ml (1/160 gallon) |
| Pint | 16 fl oz = 473.18 ml | 20 fl oz = 568.26 ml |
| Quart | 2 pints = 946.35 ml | 2 pints = 1.1365 l |
| Gallon | 3.7854 l | 4.5461 l |
Two things catch people out. The UK fluid ounce is slightly smaller than the US one, yet the UK pint is about 20% bigger, because it holds 20 fluid ounces instead of 16. And a UK gallon is about 1.2 US gallons, which matters when comparing fuel economy in miles per gallon.
Cups and spoons
Recipes are where volume causes the most confusion:
| Measure | Size | Where it is used |
|---|---|---|
| US cup | 236.59 ml | Most US recipes |
| US legal cup | 240 ml | US nutrition labels |
| Metric cup | 250 ml | Australia, New Zealand, Canada, South Africa |
| US tablespoon | 14.79 ml | US recipes |
| Metric tablespoon | 15 ml | UK, Europe and most other recipes |
| Teaspoon | 4.93 ml (US) or 5 ml (metric) | Everywhere |
For a single tablespoon the difference is tiny, but for several cups of flour or liquid it adds up: four US cups are 946 ml, while four metric cups are a full litre. Australia also uses a 20 ml tablespoon, a third bigger than elsewhere, so check where a recipe comes from.
Metric units
Metric volumes are simple by comparison. A litre is exactly one cubic decimetre, so a millilitre is the same as a cubic centimetre, the “cc” used for medicine doses and engine sizes. A cubic metre is 1,000 litres, the unit used for water bills in many countries. Centilitres appear on drinks labels (a 75 cl wine bottle holds 750 ml), and decilitres are common in Scandinavian and some European recipes.
Worked examples
- Recipe: 1.5 US cups of milk = 1.5 × 236.59 = 354.9 ml.
- Drinks: a UK pint of milk is 568 ml; a 500 ml bottle holds 0.88 UK pints or 1.06 US pints.
- Fuel: a 50-litre tank holds 50 ÷ 3.7854 = 13.2 US gallons, or 11.0 UK gallons.
- Engines: a 2.0-litre engine is 2,000 cm³, about 122 cubic inches.
Tips
- Fluid ounces are not ounces. Fluid ounces measure volume and ounces measure weight. They only match roughly for water. To weigh ingredients, use the weight converter.
- Dry measures: the US also has a dry pint and dry quart for things like berries. They are rarely used in recipes and are not included here.
- Oven temperatures also need converting for foreign recipes: use the temperature converter.
- Precision: “Auto” shows up to 10 significant digits. For cooking, 0 or 1 decimal places is plenty.
The converter runs in your browser, remembers your last units on this device only, and never sends what you type anywhere. For lengths and heights, open the length converter.