Acre Facts, History and Conversion - What is an Acre?

Acre definition

In the Middle Ages, an acre was measured as one day’s plowing for a plow team. This could vary greatly depending on the terrain. Today, an acre has been standardized in England and the U.S. as 43,560 square feet.

The acre is a unit of area in a number of different systems, including the imperial and U.S. customary systems. Its international symbol is ac. In modern times, it is equal to 1/640 of a square mile.

An acre is a measure of land area in Imperial units or U.S. customary units. It is equal to 43 560 square feet, 4840 square yards, or 160 square rods. The precise meaning of this depends on the exact definition adopted for a foot: the international acre is 4 046.856 422 4 m² (for the UK, see below). For measurements based specifically on the US survey foot the US survey acre is ca. 4 046.872 610 m².

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 equal to 4046.8564224 square metres.

During the Middle Ages, an acre was the amount of land that could be plowed in one day with a yoke of oxen.


One acre equals 0.0015625 square miles, 4,840 square yards, 43,560 square feet or about 4,047 square meters (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) 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 meters) on a side. 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 United States, Canada, and in countries where the Imperial System is still in use. As of 2010, 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.

Difference in measurement

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 meters. Consequently, the international acre is exactly 4,046.8564224 square meters.

The U.S. survey acre is about 4,046.872 609 874 252 square meters; 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. 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 meters, 160 square centimeters or 24.8 square inches), it is usually not important which one is being discussed. Areas are seldom stated to sufficient accuracy for the different definitions to be detectable.

South Asia

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.

Equivalence to other units of area

1 international acre is equal to the following metric units:

4,046.8564224 square meters

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 meters

0.404687261 hectare

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

66 feet × 660 feet (43,560 square feet)

10 square 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

43,560 square feet

160 perches. A perch is equal to a square rod (1 square rod is 0.00625 acre)

4 roods

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)

1⁄640 (0.0015625) square mile (1 square mile is equal to 640 acres)

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. The area of one acre (red) superposed on an American football field (green) and association football (soccer) pitch (blue).To be more exact, 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).

For residents of other countries, the acre might be envisaged as approximately 56.68 percent of a 105 metres (344.49 feet) long by 68 metres (223.10 feet) wide association football (soccer) pitch.

It may also be remembered as 44,000 square feet, less 1%.

History of the Acre

The measurement of an acre, though it has the same name in both the United States and Europe, is actually a slightly different measurement in each of these countries. This is due to the fact that although the acre was brought over from England, changes in the measurements in each country has led to this slight difference. So how big is an acre? Read on and see how much is an acre of land in US and UK.

The word acre came from Old English, and in its original form it meant open field. It was used to represent the amount of land that a single person could plow in a single day with a single ox and plow, which by the way, wasn’t that much, considering both the man and the ox would be quite exhausted by noon. It was also a long and straight piece of property, whereas the modern acre, since it’s just length times width, can be a square, rectangle, or anything in between.

This number varied from country to country, as some countries were easier to plow than others. It was set in stone in its current measurement in 1878 by Britain, during which time all of England copied them. This is the modern European acre.

The discrepancy actually comes from the foot used to measure the acre. The United States and Britain, partly thanks to the War of 1812, ended up with different concepts of a foot, leaving the US with a slightly larger foot, and therefore a slightly larger acre. The difference is not much though, and since land isn’t transported from one country to another, it’s not really a problem in any practical way.

So keep this in mind when you are looking for some cheap land for sale. It won’t really affect your purchasing, but it makes for an interesting topic to talk about, and brings in a lot of the US and Britain’s history.

Other acres

  • 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 U.S. 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

  • Roman acre = 1,260 square metres
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