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The acre is a unit of area used in the imperial and U.S. customary systems. It is equivalent to 43,560 square feet. An acre is about 40% of a hectare – slightly smaller than an American football field.
The acre is commonly used in the United States, Antigua and Barbuda American Samoa, the Bahamas, Belize, the British Virgin Islands, the Cayman Islands, Dominica, the Falkland Islands, Grenada, Guam, the Northern Mariana Islands, India, Jamaica, Montserrat, Myanmar, Pakistan, Samoa, St. Lucia, St. Helena, St. Kitts and Nevis, St. Vincent and the Grenadines, Turks and Caicos, and the US Virgin Islands. It is commonly used in the United Kingdom, Canada and Australia, although the metric system is used in legislation.
The international symbol of the acre is ac, and is defined as 1/640 of a square mile. The most commonly used acre today is the international acre. In the United States both the international acre and the slightly different US survey acre are in use. The most common use of the acre is to measure tracts of land. One international acre is defined as exactly 4046.8564224 square metres.
During the Middle Ages, an acre was the amount of land that could be ploughed in one day with a yoke of oxen and measured by one chain in width (22 yards), and one furlong, or 10 chains in length (220 yards), yielding 4840 square yards.
One acre equals 0.0015625 square miles, 4,840 square yards, 43,560 square feet or about 4,047 square metres (0.405 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 on which yard it is based on. Originally, an acre was understood as a selion of land sized at forty perches (660 ft or 1 furlong) long and four perches (66 ft 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 (63.63 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.
The acre is often used to express areas of land in the United States and in countries where the Imperial System is still in use. As of 2010[update], the acre is not used officially in the United Kingdom but is still often seen on estate agents' boards. In the metric system, the hectare is commonly used for the same purpose. An acre is about 40% of a hectare.
In the international yard and pound agreement of 1959 the United States and five countries of the Commonwealth of Nations defined the length of the international yard to be exactly 0.9144 metres. Consequently, the international acre is exactly 4,046.8564224 square metres.
Both the international acre and the U.S. survey acre contain 1/640 of a square mile or 4,840 square yards, but there are alternative definitions of a yard (see survey foot and survey yard), so the exact size of an acre depends on which yard it is based on. The U.S. survey acre is about 4,046.872 609 874 252 square metres; its exact value (4046 13,525,426/ m2) is based on an inch defined by 1 metre = 39.37 inches exactly, as established by the Mendenhall Order. Surveyors in the United States use both international and survey feet, and consequently, both varieties of acre.
Since the difference between the U.S. survey acre and international acre is only about a quarter of the size of an A4 sheet of paper (0.016 square metres, 160 square centimetres or 24.8 square inches), 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 India, especially in South India, residential plots are measured in cents or decimel, which is one hundredth of an acre, or 435.60 square feet (40.469 m2). In Sri Lanka the division of an acre into 160 perches or 4 roods is common.
1 international acre is equal to the following metric units:
1 United States survey acre is equal to:
1 acre (both variants) is equal to the following customary units:
Perhaps the easiest way for U.S residents to envisage 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 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 may also be remembered as 44,000 square feet, less 1%.
The word acre is derived from Old English æcer originally meaning "open field", cognate to west coast Norwegian ækre and Swedish åker, German Acker, Dutch akker, Latin ager, and Greek αγρός (agros). In English it was historically spelt aker.
The acre was approximately the amount of land tillable by a yoke of oxen 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 metres, whereas in Germany as many variants of "acre" existed as there were German states.
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 1⁄2mile (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 1⁄16of 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.
|Wikisource has the text of the 1911 Encyclopædia Britannica article Acre (land measure).|