Throughout the centuries various counting systems have been used for weights and measures: for example, the Mesopotamians used a number system based on 60, while the Mayans had a mixed calendar system based on 18 and 20. Native American tribes used a variety of number systems based on 5, 10 and 20, and until 1971 the British monetary system had 12 pennies in a shilling and 20 shillings in a pound. The binary system, based entirely on 0 and 1, is used extensively in computer science.

Most countries eventually adopted a metric system and in 1960 the international SI system (‘Système international’) of units was introduced; the metre was standardised as 1,650,763.73 wavelengths of the orange-red light from krypton-86 gas in a vacuum. Even so, some countries, including Britain and the USA, continue to use archaic systems of weights and measures.

A substantial number of metrication stamps have appeared. These include:

- a Brazilian metric ruler
- a Romanian stamp demonstrating that a metre is one ten-millionth of the distance from the north pole to the equator
- a stamp from Pakistan demonstrating the metric units of weight, capacity and length
- two Australian cartoon stamps featuring the metric conversion of length and temperature
- a Ghanaian stamp indicating that a metre of cloth is a little more than 3 feet 3 inches.

*[Australia 1973; Brazil 1962; Ghana 1976; Pakistan 1974; Romania 1966]*