The surface area of flat space shaped either as square or rectangle is computed using the following formula: A = Length x Width A = 24 ft x 24 ft = 576 square feet TIP: The problem did not specifically ask for "area", so how will you know when to use the formula for area? Easy! Only areas use "square units", such as square feet, square meters, square inch, and so forth. Therefore, when a problem asks you "how many square feet of tiles" will be needed, it actually asks for the area coverable by the tiles, which, in this case, is the floor area of the room.