Imperial system

The imperial system of units, also referred to as the imperial system, imperial units, or British Imperial, is a system of units that succeeded English units in 1824. The imperial system is still used to a degree in the United Kingdom, as well as in British territories or countries that had past British influence.

For the most part however, the UK has metricated and has defined imperial units in terms of metric units. Like the United States, the general public in the UK largely uses imperial units for everyday applications, while metric units (SI), are used in industry, science, technology, and any area where standardization of measurement is important.

The imperial and the US customary systems of measurement share many units, though their values may differ. This is because both these systems were based on English units. While units in both systems may share many of the same names, it is important to pay attention to their differences in value. Some examples of units that have different values between the systems include the ton, or tonne, a measurement of mass, the gallon, a measurement of capacity/volume, and the fathom, a measurement of length, typically used in relation to water depth.

Units of measurement

Unlike the International System of Units (SI) or other metric systems of measurement, the imperial system does not use base units that are modified by prefixes such as kilo- or centi-. All of the various base quantities in the imperial system have numerous different units representing varying sizes of the same base quantity. Below are some examples of imperial units and their equivalences to other imperial units of the same base quantity.


1 foot = 12 inches

3 feet = 1 yard

5280 feet = 1 mile


272.25 ft2= 1 perch

43560 ft2 = 1 acre


1 gallon = 160 fluid ounces

1 gallon = 8 pints

1 gallon = 4 quarts


1 pound = 16 ounces

14 pounds = 1 stone

2240 pounds = 1 ton