Litre

A litre is a unit of volume used to measure the space that a substance or liquid occupies. One litre is defined as being equivalent to one cubic decimetre (1 dm³), which is a cube with each side measuring 10 centimetres. It is also equal to 1,000 cubic centimetres (cm³) or 0.001 cubic metre (m³).

The litre is not among the base units of the International System of Units (SI) for volume, but it is an accepted unit in widespread use. The SI unit of volume is the cubic metre; the litre is a derived unit suited to everyday applications, such as the sale of beverages, petrol, and food.

Symbol and notation

The litre is denoted by the lowercase letter `l` or the uppercase letter `L`. Both are accepted; the uppercase `L` is often preferred to avoid confusion with the numeral one (1). When combined with prefixes such as milli- or centi-, one obtains the millilitre (ml, 1/1000 of a litre) and the centilitre (cl, 1/100 of a litre). A hectolitre (hl) is 100 litres.

Relationship to water and mass

When pure water is measured at standard temperature and pressure, one litre of water has a mass approximately equal to one kilogramme. This relationship arose from an earlier definition of the metric system, in which the kilogramme was defined by the volume of water. The relationship is approximate rather than exact, since the density of water changes with temperature.

History of definition

The litre originates from the metric system of France in the late 18th century. For much of the 20th century, the litre was defined as the volume of one kilogramme of water at maximum density; this definition introduced a small difference from the cubic decimetre. This definition was later abandoned, and the litre was formally fixed at 1 dm³.