Definition
A litre is defined as a special name for a cubic decimetre or 10 centimetres × 10 centimetres × 10 centimetres, (1 L ≡ 1 dm3≡ 1000 cm3). Hence 1 L ≡ 0.001 m3 ≡ 1000 cm3, and 1 m3 (i.e. a cubic metre, which is the S.I. unit for volume) is exactly 1000 L.
From 1901 to 1964, the litre was defined as the volume of one kilogram of pure water at 4 °C and 760 millimetres of mercury pressure. The kilogram was in turn specified as the mass of a platinum/iridium cylinder held at Sèvres in France and was intended to be of the same mass as the 1 litre of water referred to above. It was subsequently discovered that the cylinder was around 28 parts per million too large and thus, during this time, a litre was about 1.000028 dm3. Additionally, the mass-volume relationship of water (as with any fluid) depends on temperature, pressure, purity, and isotopic uniformity. In 1964, the definition relating the litre to mass was abandoned in favour of the current one. Although the litre is not an official SI unit, it is accepted by the CGPM (the standards body that defines the SI) for use with the SI system. CGPM defines the litre and its acceptable abbreviations.
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