Acre
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{{onesource|article|date=November 2007}}
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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|U.S. customary]] systems. The most commonly used acres today are the international acre and, in the United States, the survey acre.
One international acre is equal 4046.8564224 [[square meters|m<sup>2</sup>]]. One U.S. survey acre is equal to {{frac|62,726,400,000|15,499,969}} = 4046.8726098 m<sup>2</sup>.
[[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]]<ref>National Institute of Standards and Technology [http://ts.nist.gov/WeightsAndMeasures/Publications/upload/h4402_appenc.pdf General Tables of Units of Measurement]</ref> (which can be easily remembered as 44,000 square feet, less 1%). 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 40 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]])
* 1 chain x 10 chains ( 1-chain = 66 feet or 22 yards or 4 rods)
* 1 acre is approximately 208.71 feet x 208.71 feet (square)
* 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 west coast Norwegian language "ækre" and [[Swedish language|Swedish]] "åker", [[German language|German]] ''Acker'', [[Latin]] ''ager'' and [[Greek language|Greek]] ''αγρος'' (''agros'').
The acre was 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 enactment 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 variants of "acre" existed as there were 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, [[rood]]s, and [[perch (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]]
* '''[[Acre (Irish)|Irish acre]]'''
==References==
{{reflist}}
== See also ==
* [[Conversion of units]]
* [[Acre-foot]]
* [[Obsolete Spanish and Portuguese units of measurement]]
* [[Quarter Acre]]
==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?"]
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[[Category:Customary units in the United States]]
[[Category:Imperial units]]
[[Category:Real estate]]
[[Category:Units of area]]
[[Category:Surveying]]
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