How the volume is calculated
Rectangular: length × width × average depth × 7.48 (gallons per cubic foot). Circular: π × radius² × depth × 7.48. Oval pools use an ellipse-area factor of 0.79 relative to a rectangle of the same length and width. Average depth is (shallow end + deep end) ÷ 2 for a sloped pool.
Volume is the number every other pool task depends on: fill time from a garden hose, how much a chemical treatment costs per use, and how long a pump takes to turn over the full volume once. Getting it right the first time saves recalculating later.
Typical volumes by size
| Pool | Approx. volume |
|---|---|
| 12 ft round, 4 ft avg depth | ~3,400 gal |
| 16 × 32 ft rectangular, 5 ft avg | ~19,150 gal |
| 18 × 36 ft rectangular, 5.5 ft avg | ~26,600 gal |
Why average depth, not max depth
Using the deep-end number for the whole pool overstates volume significantly on any pool with a slope — a pool that's 3 ft at the shallow end and 8 ft at the deep end has an average depth of 5.5 ft, not 8 ft. For an L-shaped or free-form pool, it's easier to estimate the average depth by eye across the whole shape than to try to model the exact slope.
Frequently asked questions
Is this accurate enough for chemical dosing?
It's a solid starting estimate. For precise dosing, follow your test kit's instructions and treat this volume as the baseline figure it asks for.
Why 7.48 for gallons per cubic foot?
One cubic foot of water holds exactly 7.48 US gallons — it's a fixed conversion, not an estimate.
How long will it take to fill from a garden hose?
A standard garden hose delivers roughly 9–10 gallons per minute at typical household water pressure, so a 20,000-gallon pool takes somewhere around 33–37 hours of continuous filling.
Does above-ground vs in-ground change the formula?
No — the shape and dimensions are what matter, not how the pool is built. An above-ground round pool uses the same circular formula as an in-ground one.
Getting pool volume right
Pool volume starts with the pool's shape and average depth. The calculator supports common rectangular, circular and oval layouts, then converts the resulting volume into litres and gallons.
Average depth matters
If a pool has a sloped bottom, a single depth is not enough. A practical estimate uses the average of the shallow and deep depths. The result will be more useful when the measured dimensions reflect the waterline rather than the outside shell.
Why volume is useful
Volume helps with water treatment, filling estimates and comparing pump or filtration requirements. It is not, by itself, a recommendation for chemical dosage; always use the chemical manufacturer's label and the measured water conditions.
US gallons versus other gallons
The calculator uses US gallons for its gallon output. Imperial gallons are different, so users outside the United States should pay attention to the unit label when comparing the result with local specifications.