Acre
This entry is about the unit of area. For other meanings see Acre (disambiguation)An
acre is the name of a
unit of
area in a number of different systems, including
Imperial units, and
United States customary units. The most commonly used acres today are the international acre and, in the
United States, the survey acre.
There are always 4,840
square yards in an acre. Because of alternative definitions of a yard, the exact size of an acre also varies. Related units of
length are the acre's length of one
furlong (220 yards) and the acre's breadth of one
chain (22 yards).
The acre is often used to express areas of land. In the
metric system, the
hectare is commonly used for the same purpose. An acre is approximately 0.4 hectares.
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.
In
1958 the
United States and countries of the
Commonwealth of Nations defined the length of the international
yard to be 0.9144
metres. Consequently, the international acre is defined to be equal to 4,046.8564224
square metres.
The United States survey acre is defined to be equal to 4,046.87261
square metres. It is based on the United States survey
foot, which is very slightly larger than the international foot. It is the standard acre in the
United States.
1 international acre is equal to the following metric units:
* 4,046.8564224
square metres
* 0.4047
hectares
1 international acre is equal to the follwing customary units:
* 160 square
rods (1 square rod is 0.00625 acres)
* 100
Indian cents (1 cent is equal to 0.01 acres)
* 10 square
chains (1 square chain is equal to 0.1 acres)
* 4
rood (1 rood is 0.25 acres)
* 0.0015625
square miles (1 square mile is equal to 640 acres)
1 United States survey acre is equal to:
* 43,560
square feet* 4840
square yards
* 4,046.87261
square metres
* One acre equals ten square chains: ten acres equals one square furlong: an acre is a chain by a furlong: chain: 22 yards, furlong: 220 yards.
In the
United Kingdom the use of acres is now officially discouraged, but it remains a very familiar measure of land with the general public. The acre also remains the legal unit of land measure in the
United States.
The usual land tract under the
Homestead Act in the
United States is 160 acres or 0.25 square miles. This results in common field lengths of 0.5 miles, with every
rod in width equal to one acre.
The area of land is usually determined by reference to the area within its boundaries as drawn on a map. On level ground, the area of the terrain will correspond to the area on the map. On sloping ground, the area of the terrain will be greater than the area on the map.
The word "acre" is derived from
Old English æcer (originally meaning "open field",
cognate to
German Acker,
Latin ager and
Old Greek agros).
The acre was selected as approximately the amount of land tillable by one man behind an
ox in one
day. This explains one definition as the area of a rectangle with sides of length one
chain and one
furlong. 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. The word "furlong" itself derives from the fact that it is
one furrow long.
Statutory values for the acre were enacted in England by acts of:
*
Edward I,
*
Edward III,
*
Henry VIII,
*
George IV and
*
Victoria â€" the British "Weights and Measures Act" of
1878 defined it as containing 4,840 square yards.
Historically the size of farms and landed estates in the United Kingdom was always expressed in acres, even if the number of acres was so large that it might conveniently have been expressed in square miles. For example a certain landowner might have been said to own 32,000 acres of land, not 50 square miles of land.
*
Scottish acre, one of a number of
obsolete Scottish units of measurement*
Conversion of units*
Acre-foot*
Obsolete Spanish and Portuguese units of measurement*
The Units of Measurement Regulations 1995*
NIST Handbook 44
