A gram per litre or gram per liter (g/L or g/l) is a unit of measurement of mass concentration that shows how many grams of a certain substance are present in one litre of a usually liquid or gaseous mixture. It is not an SI unit because it contains the non-SI unit litre. The SI unit of mass concentration is kilogram per cubic metre, which is equivalent (1 g/L = 1 kg/m³).