Acre (ac)
Definition
The acre (symbol ac) is an imperial and US customary unit of area equal to exactly 4,046.8564224 square meters, or 43,560 square feet. It is the primary land-area unit in the United States and the United Kingdom.
History
The acre originated in medieval England as the area of land a yoke of oxen could plough in one day, roughly one furlong (660 ft) by one chain (66 ft). Edward I's statute of 1305 codified the area at 4,840 square yards, which became the modern statute acre.
The 1959 international yard and pound agreement fixed the yard at exactly 0.9144 m, which in turn fixed the international acre at exactly 4,046.8564224 m². The U.S. survey acre, based on the slightly larger U.S. survey foot, persisted in U.S. land surveys until the U.S. survey foot was officially retired on 1 January 2023.
Standard reference
Defined under the 1959 international yard and pound agreement as 4,840 × (0.9144 m)² = 4,046.8564224 m² exactly. NIST Special Publication 811 publishes this conversion factor.
Common conversions
| 1 ac | = 4,046.8564224 m² |
|---|---|
| = 43,560 ft² | |
| = 0.404686 ha | |
| = 0.00156250 mi² |