The litre (or liter; US spelling) is a unit of volume and is a non-SI metric unit with the symbol L).
1 litre is equal to the volume in a cube with edges all measuring 10cm. There are 0.22 imperial gallons in a litre. Conversely, 1 imperial gallon is equal to 4.5461 gallons.
1 litre of water weights exactly 1 kilogram.
After the metric system was introduced in France in 1791, it took a couple of years for the entire country to implement it in everyday use. After much backlash, it was decided that the cubic metre was too big for everyday use. By 1795 it was announced that the former 'cadil' (0.001 cubic metres) had been given a new name; 'litre'.
The cubic millimetre (or cubic millimeter; US spelling) is a unit of volume and is derived from an SI unit with the symbol mm³.
One cubic millimetre is defined as the volume of a cube with sides one millimetre in length. It is the same as a microlitre. It is equal to 0.000000001m³.
There are 1 billion cubic millimetres in a cubic metre.