A square mile is equivalent to 640 acres. This conversion comes from the fact that one mile is 5,280 feet, and when calculating the area of a square with sides of one mile (5,280 feet), the total area is 27,878,400 square feet. Since one acre is defined as 43,560 square feet, dividing the total square footage by the size of an acre gives 640
Therefore, one square mile contains 640 acres.
