A square foot is a measure of surface area, and a mile is a measure of length. There are 5,280 feet in a mile and 27,878,400 square feet in a square mile.
Area of a square is calculated by multiplying the length of one side by itself. A square with each side equal to one mile has an area of one square mile. Square miles have sides that are 5,280 feet in length. Multiplying 5,280 by 5,280 equals 27,878,400. The volume of a cubic mile in feet is calculated by multiplying the length of one side of the cube by itself twice. The result is 147,197,952,000 cubic feet per cubic mile.