A square foot is a unit of area in both US Customary Units as well as the Imperial System. The symbol for square foot is ft2 or sq ft. There are 27,878,400 square feet in a square mile. A square foot is calculated as the area of a square that has 1 foot on each side. What is a square mile (mi 2)? A square mile is a unit of area in both US Customary Units as well as the Imperial System. The symbol for square mile is mi 2 or sq mi. There are 0.00000004 square miles in a square foot. A square mile is calculated as the area of a square that has 1 mile on each side.