Conversion tables therefore, show the corresponding amounts or approximations between the older Imperial system and the newer metric system.

Most countries use the Metric System, an international system of physical units referred to as SI units (Système international) first proposed in England and first used in France. The system incorporates seven base units of measurement: the metre, gram, second, ampere, kelvin, candela, and mole. These bases are prefixed with twenty words like kilo, milli and centi to represent the orders of magnitude. And there are twenty-two sub-categories such as the lumen and the watt.

Before the metric system was adopted throughout Europe in 1995, the British Imperial system existed in the UK. The words denoting Imperial units are mainly from the Anglo-Saxon and Roman, originating from Italy, France and Germany. The U.S. use a similar system to the Imperial whereas Canada use the metric system. In fact there are only two other countries besides the U.S. that have not adopted the metric system.

The Imperial system measures things in inches and pounds, with orders of magnitude having their own words like mile and ton. It was first defined in the Weights and Measures Act of 1824. Only pints and miles were allowed to remain as systems of measurement in the UK after 1995.