Acre
- This article is about the unit of measure known as the acre. For other definitions, see Acre (disambiguation).
An acre is a measure of land area in Imperial units or U.S. customary units. It is equal to 43 560 square feet, or 4840 square yards. The precise meaning of this depends on the exact definition adopted for a foot: the international acre is 4046.8564 m², but the U.S. survey acre is 4046.8726 m². In the UK, an acre is defined in the as 4046.8564224 m².
A square mile has 640 acres, and a square parcel of land ¼ mile wide has 40 acres. An area of land that is one furlong (220 yards) long and one chain (22 yards) wide has an area of one acre.
In the metric system, an acre is approximately 0.4047 hectare; to a good enough approximation for many purposes, it can be taken as 0.4 hectare. Conversely, a hectare is about 2.5 acres.
The acre was selected as approximately the amount of land tillable by one man behind an ox in one day. This explains its definition of 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
Edward I,
Edward III,
Henry VIII, and
George IV;
the British "Weights and Measures Act" of 1878 defined it as containing 4840 square yards.
An acre foot is a measure of volume used in the U.S. used to measure large volumes of water.
