The formulas
One cubic foot holds 7.48 gallons — every pool-volume formula is just surface area × average depth × 7.48, with a shape factor baked in. These are the standard versions used across the industry:
rectangle: L × W × depth × 7.48 · round: D² × depth × 5.9 · oval: L × W × depth × 5.9 · kidney: (A + B) × L × depth × 3.38
The round and oval factors fold the circle's π/4 into the 7.48; the kidney version is the accepted field approximation — measure the widths at both bulges. For a straight slope, average depth is simply (shallow + deep) ÷ 2.
When to bother re-measuring
If your chlorine doses consistently overshoot or undershoot the reading change you expected, your gallons are probably off — dose response is the best volume test there is. Work backwards: if 10 fl oz of 12.5% liquid chlorine moves your pool 1.5 ppm instead of 1, your true volume is about two-thirds of what you entered.
Frequently asked questions
How accurate is a shape-based volume estimate?
Within about 5–10% for most residential pools, which is plenty for dosing — chemical targets are ranges, not bullseyes. The kidney formula is the roughest of the four (real kidneys vary); if your pool has tanning ledges, swim-outs, or a big spa spillover, round your result down slightly.
What depth do I use for a sloped pool?
Enter the shallow-end and deep-end depths and the calculator averages them — the standard approximation for a straight slope. If your pool has a long shallow shelf and a small deep hopper, the true average sits closer to the shallow number, so nudge the deep value down a bit.
Why do all the other calculators want gallons?
Every dose on this site — chlorine, acid, baking soda, salt, heater BTUs, pump turnover — scales linearly with water volume. Get gallons right once and every other number inherits the accuracy. Your result is remembered in your browser so the other tools pick it up automatically.