Measure in feet the width of the ground or wall surface that you want to pressure wash. Round up to the nearest foot. Write this measurement down for later reference.
Measure the height of the ground or wall surface that you want to pressure wash. Round up to the nearest foot. Record the measurement as well. If you are having multiple areas washed, measure their widths and heights separately.
Use a calculator to multiply the width and height of each area individually. For example, if the driveway measures 10 feet by 30 feet, the square footage of that area is 300.
Add the square footage measurements of each individual area to find the total square footage of the pressure washing job.