Litre

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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 symbol for the litre is the lowercase letter l or the uppercase letter L. A cursive or script small letter l (ℓ) is also used, but is not accepted by the BIPM.

Table of contents

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 (m�). See 1 E-3 m� 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 (cm�),
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 (m�, 1,000 litres) are used instead.

centilitre << decilitre << litre

Symbol

The symbol for the litre was originally l (lowercase letter l).

In order to reduce confusion with the number 1, L (uppercase letter L) was accepted as an alternative symbol in 1979. The United States National Institute of Standards and Technology recommends the use of the uppercase letter L.

Prior to 1979, the symbol ℓ (script small l, U+2113), came into common use in some countries; for example, it was recommended by the South African Bureau of Standards publication M33 in the 1970s. This symbol remains in common use, but is still not officially recognised by the BIPM.

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 1879, the CIPM adopted the definition of the litre, and the symbol l (lowercase letter l).

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 dm�, but it was later discovered that the original measurement was off, at 1.000 028 dm�. 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.

In 1979, at the 16th CGPM conference, the alternative symbol L (uppercase letter L) was adopted.