Liquid Volume Units
The essentials: 1 litre = 1,000 mL. 1 US gallon = 3.785 L; 1 UK gallon = 4.546 L — the imperial gallon is about 20% bigger, and so are the imperial pint, quart and fluid ounce. When a recipe or spec crosses the Atlantic, always check which gallon it means.
Metric liquid units
The metric system is refreshingly simple: everything is a power of ten of the litre, and a millilitre is exactly a cubic centimetre.
| Unit | Equals | Everyday example |
|---|---|---|
| Millilitre (mL) | 1 cm³ | A large drop is ~0.05 mL |
| Centilitre (cL) | 10 mL | Wine bottle = 75 cL |
| Litre (L) | 1,000 mL | A carton of milk |
| Cubic metre (m³) | 1,000 L | A large IBC tote is ~1 m³ |
US customary liquid units
| Unit | In mL | Builds from |
|---|---|---|
| Teaspoon (tsp) | 4.93 mL | — |
| Tablespoon (tbsp) | 14.79 mL | 3 tsp |
| Fluid ounce (fl oz) | 29.57 mL | 2 tbsp |
| Cup | 236.6 mL | 8 fl oz |
| Pint | 473.2 mL | 2 cups |
| Quart | 946.4 mL | 2 pints |
| Gallon | 3,785 mL | 4 quarts |
The US–UK gallon trap
This is the single most common source of volume errors in the English-speaking world. The two gallons are simply different sizes, and everything built from them differs too.
| Unit | US | UK (imperial) |
|---|---|---|
| Fluid ounce | 29.57 mL | 28.41 mL |
| Pint | 473 mL | 568 mL |
| Quart | 946 mL | 1,137 mL |
| Gallon | 3.785 L | 4.546 L |
Oddly, the UK fluid ounce is slightly smaller than the US one, even though the UK pint (20 fl oz) is larger than the US pint (16 fl oz). When a fuel-economy figure or a beer measure looks off by roughly a fifth, this is usually why.
Volume, weight and water
These units are where the theory meets a real job. Two-part resin is sold and mixed by fluid ounce or litre, which is why the epoxy resin volume calculator reports both; and a brewer reading gravity to find alcohol by volume is working in percentages of the batch litres, not of its weight.
One litre of pure water weighs almost exactly one kilogram — a deliberate feature of the metric system. A US gallon of water weighs about 8.34 lb, and a UK gallon about 10 lb (the old mnemonic "a pint's a pound the world around" is a US approximation; a US pint of water is 1.04 lb). To turn any volume into a weight for a specific liquid, use the volume to weight calculator.
Frequently asked questions
Is a US gallon the same as a UK gallon?
No. A US gallon is 3.785 litres, while a UK (imperial) gallon is 4.546 litres — about 20% larger. The US pint, quart and fluid ounce are all correspondingly smaller than the imperial versions.
How many millilitres are in a litre?
1,000. One litre equals 1,000 millilitres, and one millilitre equals one cubic centimetre.
How many ounces are in a US cup?
A US cup is 8 US fluid ounces, which is about 237 millilitres. A US pint is 2 cups or 16 fluid ounces.
How many litres in a gallon of water?
A US gallon of water is 3.785 litres and weighs about 3.79 kg (8.34 lb). A UK gallon is 4.546 litres and weighs about 4.54 kg (10 lb).