This article is about unit of area measure. For other uses see Acre (disambiguation).

The acre is a unit of area in a number of different systems including the imperial and U.S. customary systems. The most commonly used acres today are the international acre and in the United States the survey acre. The most common use of the acre is to measure tracts of land.

One acre comprises 4840 square yards 43560 square feet1 or about 4050 square metres (0.405 hectares) (see below). While all modern variants of the acre contain 4840 square yards there are alternative definitions of a yard so the exact size of an acre depends on which yard it is based on. Originally an acre was understood as a selion of land sized at one furlong (660 ft) long and one chain (66 ft) wide; this may have also been understood as an approximation of the amount of land an ox could plough in one day. A square enclosing one acre is approximately 208 feet 9 inches (63.63 metres) on a side. As a unit of measure an acre has no prescribed shape; any perimeter enclosing 43560 square feet is an acre in size.

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 percent of a 100 yards (91.44 metres) long by 53.33 yards (48.76 metres) wide American football field (without the end zones). The full field including the end zones covers approximately 1.32 acres (0.53 ha). It is also approximately 56.68 percent of a 105 metres (344.49 feet) long by 68 metres (223.10 feet) wide Association football (soccer) pitch. It may also be remembered as 44000 square feet less 1%; or as the product of 66 x 660. The area of one acre (red) overlaid on an American football field (green) and Association football (soccer) pitch (blue). Contents 1 International acre 2 United States survey acre 3 Equivalence to other units of area 4 Historical origin 5 Customary acre 6 Other acres 7 See also 8 References 9 External links 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 metres.2 Consequently the international acre is exactly 4046.8564224 square metres. Since the difference between the U.S. and International acre is only approximately 0.016 square metres (24.8 square inches) it is usually not important which one is being discussed. United States survey acre

The United States survey acre is approximately 4046.872 609 874 252 square metres; its exact value (4046 1352542615499969 m2) is based on an inch defined by 1 metre 39.37 inches exactly as established by the Mendenhall Order. Equivalence to other units of area

1 international acre is equal to the following metric units: 4046.8564224 square metres 0.40468564224 hectare (A square with 100 m sides has an area of 1 hectare.)

1 United States survey acre is equal to: 4046.87261 square metres 0.404687261 hectare

1 acre (both variants) is equal to the following customary units: 66 feet 660 feet (43560 square feet) 1 chain 10 chains (1 chain 66 feet 22 yards 4 rods 100 links) 1 acre is approximately 208.71 feet 208.71 feet (a square) 4840 square yards 160 perches. A perch is equal to a square rod (1 square rod is 0.00625 acre) 10 square chains 4 roods A chain by a furlong (chain 22 yards furlong 220 yards) 1/640 (0.0015625) square mile (1 square mile is equal to 640 acres) Historical origin Farm-derived units of measurement: The rod is a historical unit of length equal to 5 yards. It may have originated from the typical length of a mediaeval ox-goad. The furlong (meaning furrow length) was the distance a team of oxen could plough without resting. This was standardised to be exactly 40 rods. An acre was the amount of land tillable by one man behind one ox in one day. Traditional acres were long and narrow due to the difficulty in turning the plough. An oxgang was the amount of land tillable by one ox in a ploughing season. This could vary from village to village but was typically around 15 acres. A virgate was the amount of land tillable by two oxen in a ploughing season. A carucate was the amount of land tillable by a team of eight oxen in a ploughing season. This was equal to 8 oxgangs or 4 virgates. The word "acre" is derived from Old English cer originally meaning "open field" cognate to west coast Norwegian kre and Swedish ker German acker Latin ager and Greek (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 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 Edward III Henry VIII George IV and Queen Victoria the British Weights and Measures Act of 1878 defined it as containing 4840 square yards. Historically the size of farms and landed estates in the United Kingdom was usually expressed in acres (or acres rood s and 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 32000 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 it was subject to considerable local variation similar to the variation found in carucates virgates bovates nooks and farundels. However there were more ancient measures that were also farthingales. These may have been multiples of the customary acre rather than the statute acre. Other acres Scottish acre one of a number of obsolete Scottish units of measurement Irish acre 7840 square yards Cheshire acre 10240 square yards3 Roman acre 1260 square metres God's Acre a synonym for a churchyard.4 See also Anthropic units Conversion of units Acre-foot Spanish customary units Quarter acre French arpentalso used in Louisiana as length and area unit of measure References National Institute of Standards and Technology (n.d.) General Tables of Units of Measurement National Bureau of Standards. (1959). Refinement of Values for the Yard and the Pound. Holland Robert. (1886). A glossary of words used in the County of Chester. London: Trbner for the English Dialect Society. p. 3. The Collaborative International Dictionary of English.dead link External links Wikisource has the text of the 1911 Encyclopdia Britannica article Acre (land measure). The Units of Measurement Regulations 1995 (United Kingdom) Cockeyed.com presents "How much is inside an acre" Agricultural Measurements and Conversions