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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 4,840 square yards or 43,560 square feet.[1] While all modern variants of the acre contain 4,840 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 and 9 inches (63.6 metres) on a side. But as a unit of measure an acre has no prescribed shape; any perimeter enclosing 43,560 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-yard (91.44-meter) long by 53.33-yard (48.77-meter) wide American football field (without the end zones). The full field, including the end zones, covers approximately Template:Convert/acres. It is also approximately 56.68 percent of a 105-meter (344.49-foot) long by 68-meter (223.10-foot) wide Association football pitch (soccer field). It may also be remembered as 44,000 square feet, less 1%; or as the product of 66 x 660.

File:Acre over US and Associationl football field.svg
The area of one acre (red) overlaid on an American football field (green) and Association football field (blue).


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 4,046.856 422 4 square metres. Since the difference between the U.S. and International acre is only approximately 0.016 square meters, it is usually not important which one is being discussed.

United States survey acre

The United States survey acre is approximately 4,046.872 609 874 252 square metres; its exact value (4046 13,525,42615,499,969 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:

  • 4,046.8564224 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:

  • 4,046.87261 square metres
  • 0.404687261 hectare

1 acre (both variants) is equal to the following customary units:

  • 66 feet × 660 feet (43,560 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)
  • 4,840 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)

1 international acre is equal to the following Indian unit:

  • 100 Indian cents (1 cent is equal to 0.01 acre)

Historical origin

File:Anthropic Farm Units.png
Farm-derived units of measurement:
  1. The rod is a historical unit of length equal to 5½ yards. It may have originated from the typical length of a mediaeval ox-goad.
  2. The furlong (meaning furrow length) was the distance a team of oxen could plough without resting. This was standardised to be exactly 40 rods.
  3. 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.
  4. 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.
  5. A virgate was the amount of land tillable by two oxen in a ploughing season.
  6. 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 æcer originally meaning "open field", cognate to west coast Norwegian ækre and Swedish åker, German acker, Latin ager, and 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 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 4,221 square meters, 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
  • 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), 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 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
  • Cheshire acre = 10,240 square yards[3]
  • Roman acre = 1,260 square metres
  • God's Acre - a synonym for a churchyard.[4]

See also

  • Anthropic units
  • Conversion of units
  • Acre-foot
  • Obsolete Spanish and Portuguese units of measurement
  • Quarter acre
  • French Arpent—also used in Louisiana as length and area unit of measure


  1. National Institute of Standards and Technology (n.d.) General Tables of Units of Measurement
  2. National Bureau of Standards. (1959). Refinement of Values for the Yard and the Pound.
  3. Holland, Robert. (1886). A glossary of words used in the County of Chester. London: Trübner for the English Dialect Society. p. 3.
  4. The Collaborative International Dictionary of English.

External links


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