Why volume comes first
Every chemical dose, pump size and heater size on this site depends on how many gallons your pool holds. A pool that is 10 percent bigger than you assumed will be under-dosed by 10 percent, and a wrong volume feeds through every other calculation. The volume calculators are here to get that one number right.
How the formulas work
A rectangular pool is length × width × average depth × 7.5 gallons per cubic foot. Round and oval pools use the diameter squared, or length times width, times the average depth, times 5.9. Above-ground pools use the manufacturer’s typical wall height and fill depth, commonly 48 to 54 inches of wall. If your pool has a shallow and a deep end, use the average of the two for depth, and measure at the water line, not the pool’s outer edge.
Common sizes
The 12×24, 16×32, 20×40, 15 ft round and 24 ft round pages give the volume for standard sizes at typical depths. If yours is an unusual shape, the general pool volume calculator and the how we calculate page explain how to break it into simple shapes.