Convert volume

About the units

• Millilitres (ml) – A millilitre is one thousandth of a litre and therefore exactly one cubic centimetre. The SI Brochure treats the litre as a historical name for the cubic decimetre, and the millilitre is a legal unit across the EU and the measure for medicine doses, drinks and cosmetics. US nutrition labelling rules set a teaspoon at 5 millilitres, a tablespoon at 15 and a cup at 240. The old abbreviation “cc” means the same thing but is deprecated. For medicines a spoon should never replace millilitres, because spoon sizes vary between countries.
• Centilitres (cl) – A centilitre is one hundredth of a litre, 10 millilitres, and a legal unit in the EU and the UK. British law sets bar measures in millilitres instead: gin, rum, vodka and whisky in 25 or 35 ml, still wine in 125 or 175 ml. Standard bottles of 750 ml for still wine and 700 ml for spirits are 75 and 70 centilitres, and Sweden counts a standard drink as 4 cl of spirits. The trap is the crowded prefixes: 4 cl is 40 ml but only 0.4 dl.
• Decilitres (dl) – A decilitre is one tenth of a litre, 100 millilitres, and as a decimal submultiple of the litre a legal unit across the EU. It is the standard recipe measure in the Nordic countries and Switzerland, while British and American recipes do not use it at all, working in millilitres and cups instead. A decilitre is just under half a US cup, which holds 236.6 millilitres. The easy slip is deci against deca: one tenth against ten, a factor of a hundred apart.
• Litres (l) – The litre is not an SI unit, but the SI Brochure lists it as a historical name for a multiple of an SI unit, and the EU units directive names it explicitly: one litre is one cubic decimetre. It is the measure for drinks, fuel and package volumes across the EU, and fuel is sold in litres in the UK as well. From 1901 to 1964 the litre was instead defined as the volume of one kilogram of water, which made it 28 parts per million larger than today. Both “l” and “L” are correct symbols.
• Cubic metres (m³) – A cubic metre is the volume of a cube one metre on a side, 1,000 litres, and the SI coherent unit of volume. It sits behind British gas bills: an imperial meter reads in hundreds of cubic feet, multiplied by 2.83 to give cubic metres, and the supplier then applies a correction factor of 1.02264 and the calorific value, such as 39.5 megajoules per cubic metre, and divides by 3.6 to reach kilowatt-hours. A cubic metre of water weighs about a tonne.
• Teaspoons (tsp) – A teaspoon is 5 millilitres in metric recipes and in US nutrition labelling. The US customary teaspoon is one sixth of a fluid ounce, 4.93 millilitres, and NIST calls it an imprecise unit. Three teaspoons make a tablespoon, so tsp against tbsp is a factor of three. Medicine is where it matters: NHS guidance for liquids such as amoxicillin, sold as 125 mg in 5 ml, says not to use a kitchen teaspoon, which will not measure the right amount, but the syringe or spoon supplied.
• Tablespoons (tbsp) – A tablespoon is 15 millilitres, the figure used both in metric recipes and in US nutrition labelling. Three teaspoons of 5 millilitres make one tablespoon. There is also an older US customary tablespoon of half a fluid ounce, 14.79 millilitres. In cooking the difference does not matter, but in dosing it can: a spoon should never stand in for a figure in millilitres, because spoon sizes differ from one country to the next.
• US cups (cup) – A US cup is eight fluid ounces, one sixteenth of a gallon, which works out at exactly 236.5882365 millilitres. US nutrition labelling rules instead use a rounded statutory figure of 240 millilitres. The cup is the American recipe measure, and in the EU it may appear only as a supplementary indication. A cup is just under 2.4 decilitres, not 2.5, which is the commonest mistranslation in recipes. Two figures are therefore in circulation for the same measure, 236.6 and 240 millilitres.
• US fluid ounces (fl oz) – A US fluid ounce is one 128th of a US gallon, exactly 29.5735295625 millilitres. It is the unit on American packaging and in recipes, a US cup holds eight, and US nutrition labelling rounds it to 30 millilitres. For a British reader the trap runs both ways: it is 4.1% larger than the imperial fluid ounce of 28.41 millilitres, yet the US pint is smaller, holding 16 fluid ounces against the imperial pint’s 20. And a fluid ounce is volume, not weight.
• Imperial fluid ounces (fl oz (UK)) – An imperial fluid ounce is one twentieth of an imperial pint, exactly 28.4130625 millilitres, and 160 make an imperial gallon. Since 1 January 2000 it may appear in British trade only as a supplementary indication. The trap is that it is smaller than the US fluid ounce of 29.57 millilitres, although the imperial pint is larger: it holds 20 fluid ounces, the US pint only 16. A fluid ounce of water weighs about an ounce, 28.35 grams, and not by chance: the 1824 gallon held ten pounds of water.
• US pints (pt) – A US pint is one eighth of a US gallon, exactly 0.473176473 litres, and holds 16 US fluid ounces. It appears in American recipes and on packaging, where federal law requires a metric quantity alongside. The imperial pint poured in a British pub is a fifth larger, 568 millilitres, holding 20 imperial fluid ounces, so an American pint is about 95 ml short. The US also has a dry pint of 0.551 litres for dry goods. Neither American pint is legal for trade in the EU.
• Imperial pints (pt (UK)) – An imperial pint is one eighth of an imperial gallon, exactly 0.56826125 litres, fixed by the Weights and Measures Act 1985. It is one of the few exceptions in the EU units directive: draught beer, cider and returnable milk may still be sold by the pint in the UK, and serving sizes are regulated to a third, a half and two thirds of a pint. The imperial pint is a fifth larger than the US pint of 473 millilitres, and holds 20 fluid ounces against 16.
• US gallons (gal) – A US gallon is 231 cubic inches, which with the inch at exactly 2.54 centimetres gives 3.785411784 litres. It divides into 128 fluid ounces. The gallon is the measure for fuel and bulk liquids in the US, where federal energy statistics quote petrol in dollars per gallon, while in the EU it is not a legal trade unit. The imperial gallon is a fifth larger, 4.54609 litres, and divides into 160 fluid ounces. That gap runs straight through miles per gallon.
• Imperial gallons (gal (UK)) – An imperial gallon is exactly 4.54609 litres and divides into eight pints or 160 fluid ounces. Since 1 October 1995 it may be used in UK trade only as a supplementary indication, and fuel is sold by the litre. Yet printed car advertising must give fuel consumption in miles per gallon alongside a metric figure such as litres per 100 kilometres. The trap is the other gallon: the US gallon is 3.785 litres, so the imperial one is 20% larger and the same car shows a higher mpg in Britain.