Devised by French scientists in the late 18th century to replace the chaotic collection of units then in use. The goal of this effort was to produce a system that did not rely on a miscellany of separate standards, and to use the decimal system rather than fractions.

To obtain a standard of length a quadrant of the earth (one-fourth of a circumference) was surveyed (actually only in part) along the meridian that passes through Paris. This distance was divided into ten million parts to become the meter (spelled metre in some countries - including France (mètre)). The definition of the meter has become more and more precise through the years since. Currently the meter is the distance light travels in a vacuum in 1/299 792 458 second. The nautical mile used in modern navigation, in relation to which boat speeds and wind velocities are measured (one knot is one nautical-mile-per-hour), is defined as one minute of latitude. A degree of latitude therefore is 60 nautical miles. The quadrant of the earth measured by the French, being 90 degrees, measures 90x60 or 5400 nautical miles. Therefore: 5400 nautical miles exactly equal 10-million meters, or 10 000 kilometers.

The units most commonly used from the metric system are listed below:
  • m - meter/metre, for length.
  • kg - kilogram, for mass/weight.
  • t - ton, 1000 kg.
  • s - second, for time.
  • °C - degrees Celsius, for temperature. Water freezes at 0°C and boils at 100°C.
  • m2 square metre, for area.
  • ha - hectare, 10,000 m2.
  • l - liter/litre, for volume. 1 l of water at 4°C weighs 1 kg.
  • m3 - cubic metre, 1,000 litres.
  • m/s - metres per second - for wind speeds.
  • km/h - kilometres per hour - 3.6 metres per second - for velocities of cars/planes/bicycles/joggers
  • N - newton, for force (the force of a 1 kg weight lifted form the ground (on Earth) is about 9.82 N .. BUGGER!!)
  • kPa - kilopascal, for pressure.
  • J - joule, for energy. J=N*m.
  • W - watt, for power. 1 W = 1 J/s.
See also - English units / Metric conversion factors