1 acre = 43,560 square feet An acre is defined as one furlong (660 feet) by one chain (66 feet). There are exactly 43,560 square feet in one acre.There are 43,560 square fee … t in 1 acre. Note that acres are simple 'acres', not 'square acres'. square mile is 5,280 feet x 5,280 feet, for a total of 27,878,400 square feet. Divide that by 640 to get 43,560 square feet in an acre.