What is an acre and how does it relate to sections in the rectangular survey?

An acre is a unit of land measurement equal to 43,560 square feet, which is roughly the size of a football field without the end zones. In the rectangular survey system, one section equals 640 acres, a half section equals 320 acres, a quarter section equals 160 acres, and a quarter of a quarter section equals 40 acres. To calculate acreage from a fractional description, multiply the fractions by 640. The northwest quarter of the southeast quarter equals one quarter times one quarter times 640, which equals 40 acres. This conversion is tested frequently on real estate licensing exams. ---