An acre of land covers 43,560 square feet, so a 208.7 foot by 208.7 foot square of land is equivalent to one acre. This is 77 percent the size of an American football field or slightly smaller than 12 high school basketball courts put together.
An acre is equivalent to 0.4047 hectares or to one six-hundred-fortieth of a square mile. The definition of an acre assumes perfectly flat ground and ignores the presence of any hills. An acre of land with steeply sloped hills actually has a great surface area than an acre of flat ground. This is because in surveying only the horizontal distances between points are considered.