The imperial pint is a unit of volume in the imperial unit system with the symbol pt.
1 imperial pint is equal to 1/8 of an imperial gallon. This is equal to 1/2 imperial quart, 4 imperial gills or 20 imperial fluid ounces. In SI / metric this equates to 568.26125 ml.
In Britain, all beer, ales and stout must be served in pubs by the pint (or half pint). Every single glass, despite being a 'pint' must have the numbers 568 ml printed on the side - and because of this, is likely the most commonly known conversion factor amongst the British population.
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'.