Litre

The litre (US: liter) is a metric unit of volume. The litre is not an SI unit, but is "accepted for use with the International System". The preferred symbol is the lowercase letter l, but to avoid confusion with 1 and I the uppercase L was also allowed, in 1979. Until then uppercase letters were reserved for units derived from person names.

Table of contents

1 Definition
2 History
3 See also
4 External Links

Definition

A litre is equal to:

0.001 cubic metres,
1 cubic decimetre,
1000 cubic centimetres
the volume of a cube of side 10 centimetres.

There are 1,000 litres in a cubic metre (m³). See 1 E-3 m³ for a comparison of volumes.

The litre is subdivided into smaller units by the application of SI prefixes, making 1 litre equivalent to:

1,000 millilitres (ml) = 1,000 cubic centimetres (cm³),
100 centilitres (cl),
10 decilitres (dl),
0.01 hectolitre (hl).

Larger quantities of fluid can be measured using kilolitres (kl, 1,000 litres) or megalitres (Ml, 1,000,000 litres), but usually cubic metres (m³, 1,000 litres) are used instead.

Because the symbol l (lowercase L) can be confused with the digit 1 (and a capital "i" in some fonts), it is sometimes written in a lowercase script form. The Unicode glyph SCRIPT SMALL L (U+2113): ℓ--the symbol ℓ--can be used for this purpose. This is not in accordance to the SI, though.

centilitre << decilitre << litre

History

In 1793 the litre was introduced in France as one of the new "Republican Measures", and defined as one cubic decimetre. Its name derived from an older French unit, the litron, whose name came from Greek via Latin.

In 1901, at the 3rd CGPM conference, the litre was redefined as the space occupied by 1 kg of pure water at the temperature of its maximum density (3.98 °C) under a pressure of 1 atm. This was supposed to be 1 dm³, but it was later discovered that the original measurement was off, at 1.000 028 dm³. Furthermore the volume depends ever-so-slightly on the pressure, and pressure units include mass as a factor, introducing a circular dependency in the definition of the kilogram.

In 1964, at the 12th CGPM conference, the original definition of the litre was restored. It was recommended that the unit be used for commercial purposes but not for high-precision scientific work.