An area equal to 43,560 square feet.
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| Acre | |
|---|---|
 Comparison of some Imperial and metric units of area | |
| Unit information | |
| Unit system | US customary units |
| Unit of | Area |
| Symbol | ac |
| Unit conversions | |
| 1 ac in ... | ... is equal to ... |
| SI units | 4,046.9 m2 |
The acre is a unit of land area used in the imperial and US customary systems. It is traditionally defined as the area of one chain by one furlong (66 by 660 feet), which is exactly equal to 1⁄640 of a square mile, or 43,560 square feet, and approximately 4,047 m2, or about 40% of a hectare.
The acre is a statute measure in the United States and was formerly one in the United Kingdom and almost all countries of the former British Empire, although informal use continues.
The international symbol of the acre is ac. In the United States both the international acre and the US survey acre are in use, but they differ by only two parts per million: see below. The most common use of the acre is to measure tracts of land. The acre, based upon the International yard and pound agreement of 1959, is defined as exactly 4,046.8564224 square metres.
Traditionally, in the Middle Ages, an acre was defined as the area of land that could be ploughed in one day by a yoke of oxen.