How to Compute the Total Square Feet of a Room to Be Painted

Measure the length and width of one wall within the room. Use a tape measure and measure in inches. The length is the distance from one end of the wall to the other, and the width is the distance from the floor to the ceiling.

Multiply the length times the width of the wall. For example, if the wall was 120 inches wide and 144 inches long, you would multiply 120 times 144 to get 17,280 square inches.

Divide your answer by 144 to get square feet. In this example, you would divide 17,280 by 144 to get 120 square feet.

Find the areas of any places on the wall that would not be painted, for instance, a window. For example, if you had a window that was 36 inches wide and 60 inches long, you would multiply 36 times 60 to get 2,160 square inches. Divide by 144 to get square feet. In this example, you would divide 2,160 by 144 to get 15 square feet.

Subtract the square footage of the unpainted area from the total square footage of the wall to find how many square feet you will be painting on that wall. In this example, you would subtract 15 from 120 to get 105 square feet.

Repeat this process of measuring and calculating square feet for the other walls that you will paint. Add the square feet of painted area on each wall to get the total square footage for the room.