Acre
- This article is about the unit of measure known as the acre. For other definitions, see Acre (disambiguation).
An acre is an English unit of area, which is also frequently used in the United States and some Commonwealth countries. It is most often used to describe areas of land.
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UK definition
The UK has a definition in the system of Imperial units of the acre in The Units of Measurement Regulations 1995 as 4,046.8564224 m². This is equivalent to 43,560 square feet using the definition of foot in the same source.
U.S. customary units
The U.S. customary units definition of the acre in NIST Handbook 44 is 43,560.0 square feet. However, the U.S. has two definitions of foot (international foot and survey foot) and thus two definitions of acre:
- The international acre is 4,046.8564224 m². This is based on international foot of 0.3048 m.
- The U.S. survey acre is 4,046.87261 m². This is based on the U.S. survey foot of 1200⁄3937 m.
Related linear measurements
Two obsolete, but related, measurements are the acre's length and the acre's breadth.
- 1 acre's length = 1 furlong, 40 poles, or 220 yards
- 1 acre's breadth = 1 chain, 4 poles, or 22 yards
Conversion
An international acre may be converted to other units because it is equivalent to exactly:
- 4,046.8564224 m² (SI unit)
- 40.468564224 a,
- 0.40468564224 ha,
- 43,560 square feet,
- 4,840 square yards,
- 160 square rods,
- 4 rood,
- 1/640 square mile,
- a 10:1 rectangle of 1 furlong by 1 chain.
- 10 square chains.
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.
One acre is slightly less than 91 yards on an American Football field, with the full field, including the end zones, covering approximately 1.32 acres.
History
The acre was selected as approximately the amount of land tillable by one man behind an ox in one day. This explains its rectangular definition 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,
- George IV and
- Victoria - the British "Weights and Measures Act" of 1878 defined it as containing 4,840 square yards.
In the UK use of acres is officially discouraged, but it is still a very familiar measure of land with the general public, especially middle-aged and elderly people. Acre is measured on "flat plane", therefore land that is steeply sloped may contain more area than one acre while actually being only one acre on a map.
