|Unit system||US customary units and the British imperial systems|
|Symbol||acre or ac|
The acre is a unit of land area used in the imperial and US customary systems. It is traditionally defined as the area of one chain by one furlong (66 by 660 feet), which is exactly equal to 10 square chains, 1⁄640 of a square mile, or 43,560 square feet, and approximately 4,047 m2, or about 40% of a hectare. Based upon the International yard and pound agreement of 1959, an acre may be declared as exactly 4,046.8564224 square metres. One recognised symbol for the acre is ac,but the word "acre" is also used as the symbol.
The mile (symbol: mi2) is an imperial and US unit of measure for an area equal to the area of a square with a side length of one statute mile. Land area measurements are originally recorded as whole square meters. Square meters are converted to square kilometers by dividing by 1,000,000; square kilometers are converted to square miles by dividing by 2.58999; square meters are converted to square miles by dividing by 2,589,988.