There are 640 acres in a square mile. This answer can be found by multiplying the length of a side of a square mile by itself (640), or alternatively, by dividing the total area of a square mile (43,560) by 64. The result is 6.45 acres per side. There are 640 acres in a square mile. This answer can be found by multiplying the length of a side of a square mile by itself (640), or alternatively, by dividing the total area of a square mile (43,560) by 64. The result is 6.45 acres per side.

While it’s easy to remember that there are 640 acres in a square mile, it’s also helpful to know how this value was derived. Square miles are formed by the multiplication of one-mile^2, which yields 63360 acres in a square mile. Knowing this might be helpful if you’re ever asked to convert between square miles and acres.

A full acre is equivalent to 4,840 square feet (43,560/640 = 64*640 = 4,840). This means that a square mile would be made up of 320 full acres, or 1,728 half-acre plots.