An acre is a unit of land measurement in the U.S. customary measurement system. It is usually used to measure large areas of land such as a farm, a large residential home site, or a park. An acre is 43,560 square feet. A square that measures 208.7 feet is approximately one acre. It is roughly the size of a football field. Residential lots in a typical suburban neighborhood are roughly one-quarter to one-half of an acre. Larger home sites in the country or estate type of neighborhood are typically one acre to five acres. The term acre has been used as a basis of measurement since the middle ages. It was roughly the amount of land a person could plow in one day with the use of an ox at that time. It has been used in the transfer of land since that time.