The acre (/ˈeɪkər/AY-kər) is a
unit of land area used in the
British imperial and the
United States customary systems. It is traditionally defined as the area of one
chain by one
furlong (66 by 660 feet), which is exactly equal to 10 square chains, 1⁄640 of a square mile, 4,840 square yards, or 43,560 square feet, and approximately 4,047 m2, or about 40% of a
hectare. Based upon the
international yard and pound agreement of 1959, an acre may be declared as exactly 4,046.8564224
square metres. The acre is sometimes abbreviated ac[1] but is usually spelled out as the word "acre".[2]
Traditionally, in the
Middle Ages, an acre was conceived of as the area of land that could be
ploughed by one man using a team of 8
oxen in one day.[3]
The acre is still a statutory measure in the United States. Both the international acre and the US survey acre are in use, but they differ by only four parts per million (see below). The most common use of the acre is to measure tracts of land.
The acre is commonly used in many current and former
Commonwealth of Nations countries by custom only. In a few, it continues as a
statute measure, although since 2010 not in the UK, and not since decades ago in
Australia,
New Zealand, and
South Africa. In many of those where it is not a statute measure, it is still lawful to "use for trade" if given as supplementary information and is not used for
land registration.
Description
One acre equals 1⁄640 (0.0015625) square mile, 4,840 square yards, 43,560 square feet,[2] or about 4,047
square metres (0.4047
hectares) (see below). 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 upon the particular yard on which it is based. Originally, an acre was understood as a strip of land sized at forty
perches (660 ft, or 1
furlong) long and four perches (66 ft) wide;[4] this may have also been understood as an approximation of the amount of land a yoke of oxen could plough in one day (a furlong being "a furrow long"). A
square enclosing one acre is approximately 69.57 yards, or 208 feet 9 inches (63.61 metres), on a side. As a unit of measure, an acre has no prescribed shape; any area of 43,560 square feet is an acre.
US survey acres
In the
international yard and pound agreement of 1959, the United States and five countries of the
Commonwealth of Nations defined the international yard to be exactly 0.9144 metre.[5] The US authorities decided that, while the refined definition would apply nationally in all other respects, the
US survey foot (and thus the survey acre) would continue 'until such a time as it becomes desirable and expedient to readjust [it]'.[5] By inference, an "international acre" may be calculated as exactly 4,046.8564224 square metres but it does not have a basis in any international agreement.
Both the international acre and the US survey acre contain 1⁄640 of a square mile or 4,840 square yards, but alternative definitions of a yard are used (see
survey foot and
survey yard), so the exact size of an acre depends upon the yard upon which it is based. The US survey acre is about 4,046.872 square metres; its exact value (4046+13,525,426/15,499,969 m2) is based on an inch defined by 1 metre = 39.37 inches exactly, as established by the
Mendenhall Order of 1893.[6] Surveyors in the United States use both international and survey feet, and consequently, both varieties of acre.[7]
Since the difference between the US survey acre and international acre (0.016 square metres, 160 square centimetres or 24.8 square inches), is only about a quarter of the size of an
A4 sheet or
US letter, it is usually not important which one is being discussed. Areas are seldom measured with sufficient accuracy for the different definitions to be detectable.[8]
In the
Republic of India, residential plots are measured in square feet or square metre, while agricultural land is measured in acres.[38] In Sri Lanka, the division of an acre into 160
perches or 4
roods is common.[39]
In Pakistan, residential plots are measured in kanal (20 marla = 1 kanal = 500 sq yards) and open/agriculture land measurement is in acres (8 kanal = 1 acre or 4 peli = 1 acre) and muraba (25 acres = 1 muraba = 200 kanal), jerib, wiswa and gunta.[citation needed]
United Kingdom
Its use as a primary unit for trade in the United Kingdom ceased to be permitted from 1 October 1995, due to the 1994 amendment of the
Weights and Measures Act,[40] where it was replaced by the
hectare – though its use as a supplementary unit continues to be permitted indefinitely.[41] This was with the exemption of
Land registration,[40] which records the sale and possession of land,[42] in 2010
HM Land Registry ended its exemption.[41] The measure is still used to communicate with the public,[43] and informally (non-contract) by the farming and property industries.[44][45][46]
Equivalence to other units of area
1 international acre is equal to the following metric units:
0.40468564224 hectare (A square with 100 m sides has an area of 1 hectare.)
4,046.8564224 square metres (or a square with approximately 63.61 m sides)
A furlong by a chain (furlong 220 yards, chain 22 yards)
40 rods by 4 rods, 160 rods2 (historically fencing was often sold in 40 rod lengths[47])
1⁄640 (0.0015625) square mile (1 square mile is equal to 640 acres)
Perhaps the easiest way for US residents to envision an acre is as a rectangle measuring 88 yards by 55 yards (1⁄10 of 880 yards by 1⁄16 of 880 yards), about 9⁄10 the size of a standard
American football field. To be more exact, one acre is 90.75% of a 100-yd-long by 53.33-yd-wide American football field (without the
end zone). The full field, including the end zones, covers about 1.32 acres (0.53 ha).
For residents of other countries, the acre might be envisioned as rather more than half of a 1.76 acres (0.71 ha)
football pitch.
Historical origin
The word acre is derived from
Old Englishæcer originally meaning "open field",
cognate with west coast Norwegian ækre,
Icelandicakur,
Swedishåker, German Acker,
Dutchakker,
Latinager,
Sanskritajr, and Greek αγρός (agros). In English, an obsolete variant spelling was aker.
According to the
Act on the Composition of Yards and Perches, dating from around 1300, an acre is "40
perches [
rods] in length and four in breadth",[48] meaning 220 yards by 22 yards.[a] As detailed in the box on the right, an acre was roughly the amount of land tillable by a yoke of oxen in one day.[49]
Before the enactment of the
metric system, many countries in Europe used their own official acres. In France, the traditional unit of area was the arpent carre, a measure based on the Roman system of land measurement.
The acre was used only in
Normandy (and neighbouring places outside its traditional borders), but its value varied greatly across Normandy, ranging from 3,632 to 9,725 square metres, with 8,172 square metres being the most frequent value.[clarification needed] But inside the same pays of Normandy, for instance in
pays de Caux, the farmers (still in the 20th century) made the difference between the grande acre (68 ares, 66 centiares) and the petite acre (56 to 65 ca).[50] The Normandy acre was usually divided in 4 vergées (
roods) and 160 square perches, like the English acre.
The Normandy acre was equal to 1.6 arpents, the unit of area more commonly used in Northern France outside of Normandy. In Canada, the Paris arpent used in
Quebec before the metric system was adopted is sometimes called "French acre" in English, even though the Paris arpent and the Normandy acre were two very different units of area in ancient France (the Paris arpent became the unit of area of French Canada, whereas the Normandy acre was never used in French Canada).
In Germany, the Netherlands, and Eastern Europe the traditional unit of area was Morgen. Like the acre, the morgen was a unit of ploughland, representing a strip that could be ploughed by one man and an ox or horse in a morning. There were many variants of the morgen, differing between the different German territories, ranging from 1⁄2 to 2+1⁄2 acres (2,000 to 10,100 m2). It was also used in
Old Prussia, in the Balkans,
Norway, and
Denmark, where it was equal to about two-thirds acre (2,700 m2).
Statutory values for the acre were enacted in England, and subsequently the United Kingdom, by acts of:
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.
The acre is related to the square mile, with 640 acres making up one square mile. One mile is 5280 feet (1760 yards). In western Canada and the western United States, divisions of land area were typically based on the square mile, and fractions thereof. If the square mile is divided into quarters, each quarter has a side length of 1⁄2 mile (880 yards) and is 1⁄4 square mile in area, or 160 acres. These subunits would typically then again be divided into quarters, with each side being 1⁄4 mile long, and being 1⁄16 of a square mile in area, or 40 acres. In the United States, farmland was typically divided as such, and the phrase "the back 40" would refer to the 40-acre parcel to the back of the farm. Most of the
Canadian Prairie Provinces and the US Midwest are on square-mile grids for surveying purposes.
Legacy units
Customary acre – The customary acre was roughly similar to the Imperial acre, but it was subject to considerable local variation similar to the variation in
carucates,
virgates,
bovates, nooks, and farundels. These may have been multiples of the customary acre, rather than the statute acre.
Builder's acre = an even 40,000 square feet (3,700 m2) or 200 by 200 feet (61 m × 61 m), used in US real-estate development to simplify the math and for marketing. It is nearly 10% smaller than a survey acre, and the discrepancy has led to lawsuits alleging misrepresentation.[51]
^Minimum Standard Detail Requirements For ALTA/NSPS Land Title Surveys. Federick, MD: American Congress on Surveying and Mapping. 2021. [The stated maximum allowable "precision" (page 2) is 2 cm and 50 parts per million. An instrument consistently measuring 2 cm short would measure the area of a one international acre square, 63.614907 m on a side, as 4044.3 square metres, 2.6 square metres less than the true value, a far greater discrepancy than the difference between the international and survey acres.]
^"ed. 842". Farmers' Bulletin. U.S. Government Printing Office: 24. 1919.
^Great Britain;
Owen Ruffhead (1765).
Statutes at Large. Printed by M. Baskett. p. 421. Retrieved 12 February 2012. It is ordained that 3
grains of barley dry and round do make an
inch, 12 inches make 1
foot, 3 feet make 1 yard, 5 yards and a half make a
perch, and 40 perches in length and 4 in breadth make an acre.
^"acre, n.". Oxford English Dictionary. December 2011.
^Raymond Mensire, Le Patois cauchois, 1939, p. 55.