In order to apply the proper doses of chemicals to your pool, you need to accurately calculate how many gallons of water are in your pool. To do that, you need to know 3 numbers: the longest length of your pool, the shortest length, and the average depth. All of these numbers should be measured in feet. For a circular pool, the 2 lengths are the same and are just the pool diameter. For an oval pool, see the diagram below to know where to measure. If you have an irregular shaped pool (kidney shaped, for example), you’ll need to mentally break up the pool into smaller, regular shapes. Calculate the number of gallons in each shape, and then add them back together.