Measure the length and width of the area using a measuring tape along the edge of the wall. If the area is square, rather than rectangular, the measurements for the length and width will be the same.
Write down the measurements and multiply the two numbers together. If the room is 12 feet by 12 feet, multiply 12 times 12.
Multiply these two measurements together, and get the square footage of the area. The square footage of a 12-foot-by-12-foot room is 144 square feet.
Write down the formula ½x X x Y= square footage. Fill in the formula using the measurements of the triangular area.
Measure the base, which can be any side of the triangular area, and write the number in where the X is in the formula. If the base is 8 inches, the formula is 1/2x8xY=square footage.
Measure the height of the triangle by measuring from the top point down to the base. Put the number for the height in the Y section of the formula. If the height is 8 inches, the formula is 1/2x8x8=square footage.
Multiply the numbers together. If the base is 8 inches and the height is 8 inches, the formula is 1/2x8x8=square footage, and the square footage is 32.
Find the square footage for a circular area by using the formula, 3.14 x ½ x X² = square footage. Measure the length across the circle, and divide the number in half. If the length is 10 feet, the radius is 5 feet.
Put the number for the radius into the formula in the X spot. The formula is 3.14 x ½ x 5²=square footage.
Multiply 3.14 by ½x your circle's radius measurement, and find the square footage in that circle. Going back to the example, 3.14 x ½ x 5² =39.25 sq. ft.