- This article is about the unit of measure known as the acre. For other definitions, see Acre (disambiguation).
An acre is an English measure of land area of about 0.4 ha. The word has also been used for foreign measures of a similar size.
UK definition
In the UK the acre is listed in The Units of Measurement Regulations 1995 as 4 046.856 422 4 m², which works out to be 43 560 square feet of 0.3048² m² (international definition of 1959).
US definition
In the United States, the NIST states in NIST Handbook 44 that it is 43 560 square feet. However, the United States maintain two definitions of foot:
- The international foot of 0.3048 m, thus the international acre is 4 046.856 422 4 m² exactly and
- the survey foot of 1200/3937 m, thus the survey acre is 4 046.872 61 m² approximately.
Conversion
An international acre is equivalent to exactly:
An acre is equivalent to approximately:
One square mile is 640 acres. A square parcel of land ¼ mile wide is 40 acres. A square parcel of land ½ mile on a side is 160 acres, the usual land tract under the Homestead Act in the United States. This results in common field lengths of ½ mile, with every rod in width equal to one acre.
History
The acre was selected as approximately the amount of land tillable by one man behind an ox in one day. This explains its definition in terms of the non-square one-chain by one-furlong parcel of land; a long narrow strip of land is more efficient to plough than a square plot, since the plough does not have to be turned so often. Statutory values were enacted in England by acts of
See also
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