English units

English units are the historical units of measurement used in England up to 1826 (when they were replaced by Imperial units), which evolved as a combination of the Anglo-Saxon and Roman systems of units. Various standards have applied to English units at different times, in different places, and for different applications.

The two main sets of English units were the Winchester Units, in effect from 1495–1587, as reaffirmed by King Henry VII, and the Exchequer Standards, in effect from 1588–1825, as first defined by Queen Elizabeth I.

The units were replaced by Imperial Units in 1824 (effective January 1, 1826) by a Weights and Measures Act, which retained many but not all of the unit names and redefined many of the definitions.

Use of the term "English units" is ambiguous, as it is sometimes mistakenly used to refer to the Imperial units used in the UK, or to United States customary units, which retain some unit names of English Units, but has somewhat different definitions. (The terms imperial units or imperial measurements are used in the UK to refer to the non-metric system since they were used as a standard throughout the British Empire and the Commonwealth.)

Very little is known of the measurement units of the British Isles prior to Roman colonization in the 1st century CE. During the Roman period, Roman Britain relied on Ancient Roman units of measurement. During the Anglo-Saxon period, the North German foot of 335 millimetres (13.2 inches) was the nominal basis for other units of linear measurement. The foot was divided into 4 palms or 12 thumbs. A cubit was 2 feet, an elne 4 feet. The rod was 15 Anglo-Saxon feet, the furlong 10 rods. An acre was 4 × 40 rods, i.e., 160 square rods or 36,000 square Anglo-Saxon feet. However, Roman units continued to be used in the construction crafts and reckoning by the Roman mile of 5000 feet or 8 stades continued, in contrast to other Germanic countries who adopted the name "mile" for a longer native length closer to the league. From the time of Offa King of Mercia (8th century) until 1526 the Saxon pound, also known as the moneyers' pound (and later known as the Tower pound) was the fundamental unit of mass measurement.

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