Acre

Description

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. 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.

Differences between international and 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 metres. Consequently, the international acre is exactly 4,046.8564224 square metres.

Both the international acre and the US 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 upon. The US survey acre is about 4,046.872609874252 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. 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 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.

South Asia

In India, residential plots are measured in cents or decimal, 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:

1 United States survey acre is equal to:

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

Perhaps the easiest way for US 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).

For residents of other countries, the acre might be envisaged as approximately half 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%.

Historical origin

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, Sanskrit ajr, and Greek αγρός (agros). In English it was historically spelled 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  ¹⁄₂ 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 acres