The official definition of an acre: a common measure of area: in the U.S. and U.K., 1 acre equals 4,840 square yards (4,047 square meters) or 0.405 hectare; 640 acres equals one square mile. The visual definition might be easier to ‘see’. When trying to decide how much land you want your home to be on, the size of a football field equals about an acre. If you aren’t into football, then how about 15 1/2 tennis courts or a 70 yard golf shot. An acre is also about 150 parked cars, or for fun – 696,000 post it notes!