Multiply the length by the width of the desired patio area to obtain the total square feet.
Multiply the length by the width of the brick you plan to use. A standard brick is 4 inches by 8 inches, or 32 square inches. Add 1/2-inch to the length and width measurement before multiplying if you plan to use mortar between the bricks.
Divide 144, the number of square inches in one square foot, by the square inches of the brick to determine the number of bricks needed to cover 1 square foot of patio surface. For the standard brick size of 32 square inches, 4.5 bricks are needed to cover 1 square foot of patio.
Multiply the number of bricks needed to cover 1 square foot by the number of square feet in the patio. A patio measuring 15 by 20 has 300 square feet of surface area and, using the standard brick size, will require 1,350 bricks.