To measure the area of the countertop you need to buy, first measure the countertop length in inches, adding 1 1/2 inches of overhang at each end. Divide the length by 12 to calculate the linear feet of your countertop. Then, use the same process to measure your countertop’s depth (it’s usually 25 inches or 25 5/16 inches) in linear feet, being sure to account for your cabinets and overhang. Then, multiply the linear feet of the depth and width to get the square footage of your countertop.