The acre is a unit of land area used in the imperial and US customary systems. It is traditionally defined as the area of one chain by one furlong, which is exactly equal to 10 square chains, of a square mile, 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 square metres. One recognised symbol for the acre is ac, but the word 'acre' is also used as the symbol.
The acre is a statute measure in the United States, in the United Kingdom and in almost all countries of the former British Empire: in most it is lawful to 'use for trade' if given as supplementary information and is not used for land registration.
In the United States both the international acre and the US survey acre are in use, but they differ by only two parts per million: see below. The most common use of the acre is to measure tracts of land.
Traditionally, in the Middle Ages, an acre was defined as the area of land that could be ploughed in one day by a yoke of oxen.
DescriptionOne acre equals square mile, 4,840 square yards, 43,560 square feet, or about . 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 selion of land sized at forty perches long and four perches wide; this may have also been understood as an approximation of the amount of land a yoke of oxen could plough in one day. A square enclosing one acre is approximately 69.57 yards, or 208 feet 9 inches 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 acresIn 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. The US authorities decided that, while the refined definition would apply nationally in all other respects, the US survey foot would continue 'until such a time as it becomes desirable and expedient to readjust '. By inference, an "international acre" may be calculated as exactly square metres but it does not have a basis in any international agreement.
Both the international acre and the US survey acre contain of a square mile or 4,840 square yards, but alternative definitions of a yard are used, so the exact size of an acre depends upon which yard it is based. The US survey acre is about 4,046.872 square metres; its exact value is based on an inch defined by 1 metre = 39.37 inches exactly, as established by the Mendenhall Order of 1922. Surveyors in the United States use both international and survey feet, and consequently, both varieties of acre.
Since the difference between the US survey acre and international acre, 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.
In October 2019, U.S. National Geodetic Survey and National Institute of Standards and Technology announced their joint intent to end the 'temporary' continuance of the US survey foot, mile and acre units, with effect from the end of 2022.
Spanish acreThe Puerto Rican cuerda is sometimes called the "Spanish acre" in the continental United States.
UseThe acre is commonly used in a number of current and former Commonwealth countries by custom, and in a few it continues as a statute measure. These include Antigua and Barbuda, American Samoa, The Bahamas, Belize, the British Virgin Islands, the Cayman Islands, Canada, Dominica, the Falkland Islands, Grenada, Ghana, Guam, the Northern Mariana Islands, Jamaica, Montserrat, Samoa, Saint Lucia, St. Helena, St. Kitts and Nevis, St. Vincent and the Grenadines, Turks and Caicos, the United Kingdom, the United States and the US Virgin Islands.
South AsiaIn India, residential plots are measured in square feet while agricultural land is measured in acres. In Sri Lanka, the division of an acre into 160 perches or 4 roods is common.
In Sindh, residential plots as well as open/agriculture land measurement is in Acres, Jareb, Wiswa and Gunta.
United KingdomIts 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, where it was replaced by the hectare though its use as a supplementary unit continues to be permitted indefinitely. This was with exemption of Land registration, which records the sale and possession of land, in 2010 HM Land Registry ended its exemption. The measure is still used to communicate with the public, and informally by the farming and property industries.
Equivalence to other units of area1 international acre is equal to the following metric units:
- 0.40468564224 hectare
- 4,046.8564224 square metres
- 0.404687261 hectare
- 4,046.87261 square metres
- 66 feet × 660 feet
- 10 square chains
- 1 acre is approximately 208.71 feet × 208.71 feet
- 4,840 square yards
- 43,560 square feet
- 160 perches. A perch is equal to a square rod
- 4 roods
- A furlong by a chain
- 40 rods by 4 rods, 160 rods2
- square mile
For residents of other countries, the acre might be envisioned as rather more than half of a football pitch.
It may also be remembered as 1% short of 44,000 square feet.
Historical originThe word "acre" is derived from Old English æcer originally meaning "open field", cognate with west coast Norwegian ækre, Icelandic akur, Swedish åker, German Acker, Dutch akker, Latin ager, Sanskrit ajr, and Greek αγρός. In English, it was historically spelled .
According to the Act on the Composition of Yards and Perches, dating from around 1300, an acre is "40 perches
Before the enactment of the metric system, many countries in Europe used their own official acres. In France, the acre was used only in Normandy, 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. The Normandy acre was usually divided in 4 vergées 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.
In Germany there were many variants of the Acker, differing between the German states:
|Place||Name||Area in m²||Area in |
|Grand Duchy of Baden||Badischer Morgen||3,600||400|
|Bergisches Land||Bergischer Morgen||2,132||120|
|Cologne, Rhineland||Rheinländischer Morgen||3,176||150|
|Frankfurt am Main||Feldmorgen||2,025||160 QFeldR|
|Frankfurt am Main||Waldmorgen||3,256||160 QWaldR|
Statutory values for the acre were enacted in England, and subsequently the United Kingdom, by acts of:
- Edward I
- Edward III
- Henry VIII
- George IV
- Queen Victoria – the British Weights and Measures Act of 1878 defined it as containing 4,840 square yards.
The acre is related to the square mile, with 640 acres making up one square mile. One mile is 5280 feet. 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 mile and is square mile in area, or 160 acres. These subunits would typically then again be divided into quarters, with each side being mile long, and being 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.
- 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.
- Builder's acre – In US construction and real estate development, an area of 40,000 square feet. Used to simplify math and for marketing, it is nearly 10% smaller than a survey acre.
- Scottish acre, one of a number of obsolete Scottish units of measurement
- Irish acre = 7,840 square yards
- Cheshire acre = 10,240 square yards
- Stremma or Greek acre ≈ 10,000 square Greek feet, but now set at exactly 1,000 square metres
- Dunam or Turkish acre ≈ 1,600 square Turkish paces, but now set at exactly 1,000 square metres
- Actus quadratus or Roman acre ≈ 14,400 square Roman feet
- God's Acre – a synonym for a churchyard.
- Long acre the grass strip on either side of a road that may be used for illicit grazing.