Draw a rough diagram of the shape of your countertops. If the countertops are L- or U-shaped, separate the diagram into rectangles by drawing lines on the diagram from the inside corners straight back to the back edge of the countertops.
Measure the depth of your countertops by measuring from the back wall to the front edge. This width will be the same for the entire countertop, so write this measurement as the width for each of the rectangular sections.
Measure the length of the countertops, following your diagram as a guide for where to measure. Measure the length of each rectangular section as you have separated them on your diagram. Write the measurements in inches on the sections of your diagram.
Multiply the width by the length for each of the rectangles on your diagram, using a calculator. Write the number in the center of each rectangle.
Add the numbers in the center of each rectangle together with a calculator. This is the total number of square inches that your countertops cover. Use a calculator to divide the number of square inches by 144. The result is the square footage of your countertops.