Acre

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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, 43,560 square feet[1] or about 4,046.86 square meters (0.404686 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 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 meters) 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 yards (91.44 meters) long by 53.33 yards (48.76 meters) 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 meters (223.10 feet) 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.

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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 meters.[2] Consequently, the international acre is exactly 4,046.856 422 4 square meters. 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.