Units of measurement in the metric system. Metric units include the metre, centimetre, millimetre, kilometre, gram, kilogram, litre and millilitre. The metric system was developed in the 18th century in France. Most of the world now uses a modern form of metric units known as SI units (Système International d'Unités in French), especially in science and technology. Some exceptions exist, for example in the UK draught beer must be sold in pints, and speedometers must diplay miles per hour, which are imperial units.