Acre

{{otheruses1|the unit of measurement}}
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{{onesource|article|date=November 2007}}
The '''acre''' is a [[Units of measurement|unit]] of [[area]] in a number of different systems, including the [[Imperial unit#Measures of area|imperial]] and [[United States customary units#Units of area|US customary]] systems. The most commonly used acres today are the international acre and, in the United States, the survey acre.

[[Image:Acre over football field.svg|frame|The area of one acre (red) overlaid on an American football field]]
One acre comprises 4,840 [[square yard]]s or 43,560 [[square feet]]. Because of alternative definitions of a yard or a foot, the exact size of an acre also varies slightly. Originally, an acre was a [[selion]] of land one [[furlong]] long and one [[chain (unit)|chain]] wide. However, an acre is a measure of area, and has no particular width, length or shape.

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 40% of a hectare.

One acre is 90.75 yards of a 53.33-yard-wide [[American football]] field. The full field, including the end zones, covers approximately 1.32 acres.

==International acre==
In 1958, the [[United States]] and countries of the [[Commonwealth of Nations]] defined the length of the international [[yard]] to be 0.9144 [[meter]]s.<ref>National Bureau of Standards. [http://geodesy.noaa.gov/PUBS_LIB/FedRegister/FRdoc59-5442.pdf Refinement of Values for the Yard and the Pound].</ref> Consequently, the international acre is exactly 4046.8564224 [[square meters]].

==United States survey acre==
The United States survey acre is approximately 4046.873 [[square meter]]s; its exact value ({{frac|4046|13,525,426|15,499,969}} m²) is based on an inch defined by 1 meter = 39.37 inches exactly, as established by the [[Mendenhall Order]]. It is the standard acre in the [[United States]], but the fractional difference from the international acre is only 4 millionths, or 4 ten-thousandths of one percent.

==Equivalence to other units of area==
1 international acre is equal to the following metric units:
* 4046.8564224 [[square meter]]s
* 0.40468564224 [[hectare]]

1 United States survey acre is equal to:
* 4046.87261 [[square meter]]s
* 0.404687261 [[hectare]]

1 acre (both variants) is equal to the following customary units:
* 66 feet × 660 feet (43,560 [[square foot|square feet]])
* 4840 [[square yard]]s
* 160 [[Perch (area)|perches]]. A perch is equal to a square [[rod (unit)|rod]] (1 square rod is 0.00625 acre)
* 10 square [[chain (unit)|chain]]s
* 4 [[rood]]s
* A chain by a furlong (chain 22 yards, furlong 220 yards)
* 0.0015625 [[square mile]] (1 square mile is equal to 640 acres)

1 international acre is equal to the following Indian unit:
* 100 [[India]]n [[cent (measure)|cent]]s (1 cent is equal to 0.01 acre)

== Historical origin ==
The word "acre" is derived from [[Old English]] ''æcer'' (originally meaning "open field", [[cognate]] to [[German language|German]] ''Acker'', [[Latin]] ''ager'' and [[Greek language|Greek]] ''αγρος'' (''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 (length)|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''.

Before the ennactment of the [[metric system]], many countries in Europe used their own official acres. These were differently sized in different countries, for instance, the historical French acre was 4221 square metres, whereas in Germany as many acres existed as German states.

Statutory values for the acre were enacted in England by acts of:
* [[Edward I of England|Edward I]],
* [[Edward III of England|Edward III]],
* [[Henry VIII of England|Henry VIII]],
* [[George IV of the United Kingdom|George IV]] and
* [[Victoria of the United Kingdom|Victoria]] – 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 usually expressed in acres (or acres, [[roods]], and [[perches (area)|perches]]), 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.

==Customary acre==
The customary acre was a measure of roughly similar size to the acre described above, but was subject to considerable local variation. However, there were more ancient measures that were also used, including [[carucate]]s, [[virgate]]s, [[bovate]]s, [[nook]]s, and farundells or farthingales. These may have been multiples of the customary acre, rather than the statute acre.

==Other acres==
* '''[[Acre (Scots)|Scottish acre]]''', one of a number of [[obsolete Scottish units of measurement]]

==References==
{{reflist}}

== See also ==
* [[Conversion of units]]
* [[Acre-foot]]
* [[Obsolete Spanish and Portuguese units of measurement]]

==External links==
* [http://www.opsi.gov.uk/si/si1995/Uksi_19951804_en_2.htm The Units of Measurement Regulations 1995 (United Kingdom)]
* [[Cockeyed.com]] [http://cockeyed.com/inside/acre/acre.html presents "How much is inside an acre?"]



[[Category:Customary units in the United States]]
[[Category:Imperial units]]
[[Category:Real estate]]
[[Category:Units of area]]

[[ast:Acre (unidá de superficie)]]
[[bn:একর]]
[[bs:Acre]]
[[bg:Акър]]
[[cs:Akr]]
[[da:Acre (arealenhed)]]
[[de:Acre (Einheit)]]
[[et:Aaker]]
[[es:Acre (unidad de superficie)]]
[[eo:Akreo (mezurunuo)]]
[[fr:Acre (unité)]]
[[gd:Acair (talamh)]]
[[gl:Acre (unidade de superficie)]]
[[ko:에이커]]
[[hr:Acre (jedinica)]]
[[bpy:একর]]
[[it:Acro]]
[[he:אקר]]
[[la:Ager (mensura)]]
[[mk:Акра (мерна единица)]]
[[nl:Acre (oppervlaktemaat)]]
[[ja:エーカー]]
[[no:Acre (måleenhet)]]
[[pl:Akr]]
[[pt:Acre (unidade)]]
[[ru:Акр]]
[[simple:Acre]]
[[sk:Aker (jednotka)]]
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[[ta:ஏக்கர்]]
[[vi:Mẫu Anh]]
[[uk:Акр]]
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