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Convert litres, millilitres, gallons, quarts, pints, and cups between metric and US/UK systems. All calculations run in your browser.
The most important thing to know about volume conversion is that the US and UK use different definitions for the same unit names. A US gallon is 3.78541 litres. A UK imperial gallon is 4.54609 litres. That is a 20% difference. If a fuel economy spec lists "miles per gallon" without specifying which gallon, the figure is ambiguous.
The same divergence applies down the chain. A US pint is 473 ml; a UK pint is 568 ml. A US fluid ounce is 29.5735 ml; a UK fluid ounce is 28.4131 ml. When following a recipe or dispensing medication, the country of origin of the recipe determines which fluid ounce applies.
The metric system avoids this ambiguity. The litre is defined as exactly one cubic decimetre (0.001 m³). A millilitre is one cubic centimetre. These definitions are internationally fixed. Most countries outside the US and UK now use metric volume exclusively in commerce and science.
Cooking measurements add another layer. The cup is a US volume unit equal to 8 US fluid ounces, or about 236.6 ml. A tablespoon is 1/16 of a cup, approximately 14.8 ml. A teaspoon is 1/3 of a tablespoon, about 4.9 ml. These units are not used in UK or metric recipes, which measure by weight in grams for dry ingredients and millilitres for liquids.
In chemistry, the millilitre and litre are the standard working units. Glassware is calibrated in ml; solution concentrations are expressed per litre (molar = mol/L). Pharmaceutical liquid dosing also uses millilitres, which is why medicine cups and droppers are labelled in ml regardless of the patient's country.
Fuel is sold by the litre in most countries and by the US gallon in the United States. Aviation fuel is bought and sold in US gallons, but aircraft fuel tanks are often measured in litres or kilograms by weight, since fuel density matters for weight-and-balance calculations. Knowing the conversion (1 US gallon of Jet-A weighs about 6.7 lbs, or roughly 3.04 kg) is routine in flight operations.
How many litres are in a US gallon?
One US liquid gallon equals exactly 3.785411784 litres. The UK imperial gallon is larger at 4.54609 litres.
How many millilitres are in a cup?
One US legal cup (used in nutrition labelling) is exactly 240 ml. One US customary cup is 236.588 ml. Most recipes treat 240 ml as close enough for cooking purposes.
Why is a UK pint larger than a US pint?
The US pint (473 ml) and UK imperial pint (568 ml) diverged historically because the US adopted older English wine measures while the UK later standardised on the imperial system. Both are "pints" but they never agreed on a common definition.