Sketch the space in which you plan to install the backsplash. Divide the space into rectangles.
Measure the length and width of each rectangle using a tape measure. Write your measurements on your sketch.
Multiply the length and width of each rectangle to determine its area. For example, you may have one rectangle that is 36 inches by 4 inches and another that is 48 inches by 4 inches. Multiply 36 by 4 to get 144 square inches for the first rectangle. Multiply 48 by 4 to get 192 square inches for the second rectangle.
Add the areas of the individual rectangles to determine the total area. In this example, you would add 144 and 192 to get 336 square inches.
Convert from square inches to square feet, if necessary, by dividing by 144. In this example, you would divide 336 by 144 to get 2.33 square feet.