How the math works
Chlority mathGallons = length × width × average depth × a shape factor. A cubic foot holds 7.48 gallons, so rectangles use 7.48; round and oval pools use 5.9 (7.48 × π/4); kidney and freeform pools use 6.7 as an approximation. Average depth = (shallow + deep) ÷ 2.
LimitsFreeform pools, steps, sun shelves and sloped walls make any formula approximate. If you know your volume from the builder or from a salt-cell reading, use that.
Questions
How many gallons is a typical in-ground pool?
A 16 x 32 ft pool with 3.5 to 6 ft depths holds about 18,000 gallons; many backyard in-ground pools are between 15,000 and 30,000 gallons.
How do I measure an above-ground pool?
Use the inside diameter (or length and width for an oval) and the actual water depth, usually 6 to 12 inches below the wall height.