Acres

An acre (ac) is a unit of area in the in the US customary and imperial systems of measurement. It is mostly used to measure relatively large land areas in the US, UK, and former British Commonwealth countries to some degree, and has traditionally been defined as 66 × 660 feet; this is the area formed by 1 chain by 1 furlong, two units of length in the US customary and imperial systems of measurement.

In the International System of Units (SI), area is measured in units of square meters (m²). It is important to be able to convert between the US customary and imperial systems of measurement and SI, since most countries around the world primarily use SI. Below are the relationships between some commonly used measurements of area.

1 acre = 43,560 ft²

640 acres = 1 mi²

1 acre = 4046.856 m²

1 survey acre ≈ 4046.873 m²

Note that these conversions are rounded to 3 decimal places, so they are not exact.

The survey acre is the definition of the acre in the US prior to the redefinition of the yard in 1959. Although their values vary only slightly, the US continued using the old definition of the acre, referring to it as the survey acre. Practically though, areas are typically not measured accurately enough for the small difference between the acre and survey acre to be particularly relevant.