Calculating the number of sections needed is easier than you may think. You should leave about 3 feet around the fence, so mark off this distance around the entire pool. Then use a tape measure to measure the entire distance around the pool. When you choose your fence, do some simple math to figure out how many sections you need. For instance, if the distance measures 60 feet and the sections are 12 feet each, you would divide 60 by 12, which equals 5 sections for a complete fence.