For above-ground pools, you simply have to count the number of spaces your pool has in-between the posts. This will be how many panels you will need. They are sold according to panel pieces, so look for that in the selection of options. For the in-ground pools, you will need to know the size of the perimeter of the pool. These fences are also sold in panels, usually of twelve-foot lengths, in a kit. Several of the pool models have three kits offered as A, B, and C. One of these will be the base kits that you begin with, and it is usually the largest and most expensive of the three. From there, you will need to determine how many of the others you need to fit the entire perimeter.