Volume units and their equivalents
| Unit | Symbol | In liters |
|---|---|---|
| Cubic meter | m³ | 1,000 l |
| Liter | l | 1 lbase unit |
| Centiliter | cl | 0.01 l |
| Milliliter | ml | 0.001 l |
| US gallon | gal | 3.78541 l |
| Imperial gallon | gal UK | 4.54609 l |
| US pint | pt | 0.473176 l |
| US fluid ounce | fl oz | 0.0295735 l |
| US quart | qt | 0.946353 l |
| Imperial pint | pt UK | 0.568261 l |
| US cup | cup | 0.236588 l |
| Tablespoon | tbsp | 0.0147868 l |
| Teaspoon | tsp | 0.00492892 l |
| Deciliter | dl | 0.1 l |
| Oil barrel | bbl | 158.987 l |
Frequently asked questions
Why do US and UK gallons differ?
The British imperial gallon is 4.546 l, the US one 3.785 l, about 20% smaller. Both countries kept distinct historical definitions when standardising. Fuel economy in miles per gallon therefore looks better in the UK for identical performance.
Is a milliliter the same as a cubic centimeter?
Yes, exactly: 1 ml = 1 cm³. Syringes and engines are often graduated in cm³ (or cc) and food liquids in ml, but it is the same volume.
Has the litre always been exactly one cubic decimetre?
No. From 1901 to 1964 the litre was defined as the volume of one kilogram of pure water at its densest, which came to 1.000028 dm³. Everything published in litres during those sixty-three years therefore carries a 28 parts per million offset, invisible in a kitchen and real in a laboratory. The 12th General Conference on Weights and Measures restored the exact equality 1 l = 1 dm³ in 1964, and advised against the litre for high precision work.
Do two volumes add up when mixed?
Not always. Pour 50 ml of ethanol into 50 ml of water and you get about 96 ml, not 100: the smaller molecules settle into the gaps between the larger ones and the mixture contracts by roughly 4 %. Mass, on the other hand, is always additive, which is one more reason spirits and syrups are made up by weight in industry. Water with water, or oil with oil, adds up normally.
Why does a cubic metre hold so much?
Because volume grows with the cube of the dimensions: 1 m³ is 1000 litres, and doubling every side multiplies capacity by eight, not by two. An aquarium 100 by 40 by 50 cm holds 200 litres; the same tank with every dimension doubled would hold 1600. It also explains the surprise at an order placed in cubic yards, common for concrete and topsoil in the United States: one cubic yard is 764.6 litres, about three quarters of a cubic metre.
The litre is not an SI unit
The SI measures volume in cubic metres. The litre is not one of its units: it is accepted for use with the SI as a convenience, and has been exactly one cubic decimetre since 1964. That date matters. From 1901 to 1964 the litre was defined as the volume of one kilogram of pure water at its maximum density, which made it twenty-eight parts per million larger than the cubic decimetre. The gap troubled no kitchen and troubled analytical chemistry a great deal, so the General Conference on Weights and Measures dropped the older definition.
The gallon has never been one unit but two. The US gallon is 3.785411784 litres and descends from the Queen Anne wine gallon, fixed in 1707 at 231 cubic inches. The British imperial gallon is 4.54609 litres and was defined in 1824 as the volume of ten pounds of water. Twenty per cent separates them. A car advertised at thirty miles per gallon therefore burns 7.84 litres per hundred kilometres on the American figure and 9.42 on the British one.