Pool Volume Calculator: how many gallons is your pool?
Every chemical dose, salt fill, heater size, and pump setting starts with one number — and the shortcut most calculators use gets it wrong. The (shallow + deep) ÷ 2 average assumes your bottom is an even ramp; a real diving pool is mostly shallow water, and the shortcut overstates its volume by 10–15% — thousands of gallons, and every dose with it. This calculator handles the shapes and depth profiles pools actually have.
How many gallons is your pool?
Pick your shape, measure at the waterline, and get the real number — the one every chemical dose, salt fill, heater size, and pump setting depends on. The math updates live.
Measure water, not walls: use the waterline length/width and the actual water depth (an above-ground pool with a 52″ wall holds ~48″ / 4 ft of water).
Rectangle, round, and both ovals are exact geometry at 7.48 gal/ft³ (most calculators round to 7.5). Kidney/freeform uses the industry 0.45 × (A + B) × length approximation — treat it as ±5%. The diving-pool mode weights each section by its share of the pool's length; it's the difference between a chemical dose that's right and one that's 10–15% hot.
Common pool sizes (instant answers)
Computed with the same math as the calculator — exact geometry at 7.48 gal/ft³. In-ground rectangles assume the standard 3.5 → 6.5 ft even slope (5 ft average); above-ground pools assume 4 ft of water (a 52″ wall). Your pool differs? Use the calculator.
| 12 × 24 ft | ~10,772 gal |
| 14 × 28 ft | ~14,662 gal |
| 15 × 30 ft | ~16,831 gal |
| 16 × 32 ft | ~19,150 gal |
| 18 × 36 ft | ~24,237 gal |
| 20 × 40 ft | ~29,922 gal |
| 12 ft round | ~3,384 gal |
| 15 ft round | ~5,288 gal |
| 18 ft round | ~7,614 gal |
| 21 ft round | ~10,364 gal |
| 24 ft round | ~13,536 gal |
| 27 ft round | ~17,132 gal |
| 30 ft round | ~21,151 gal |
| 12 × 24 ft oval | ~7,693 gal |
| 15 × 30 ft oval | ~12,020 gal |
| 18 × 33 ft oval | ~15,693 gal |
Why our math is different (and when it matters)
We use 7.48 gallons per cubic foot, not 7.5. Small, but it's a 0.3% overstatement rivals bake into every result for no reason.
We ask which oval you have. A true ellipse and a rounded-rectangle "stadium" oval (straight sides, semicircular ends — what most above-ground oval pools actually are) differ by up to ~12% at the same length and width. Most calculators quietly apply one constant to both and never tell you which.
We don't trust the average-depth shortcut on diving pools. (Shallow + deep) ÷ 2 is only correct when the bottom is one even ramp. A diving pool is a shallow flat, a short slope, and a deep hopper — the diving mode weights each section by its share of the pool's length instead.
The honest limit: kidney and freeform pools use the industry 0.45 × (A + B) × length approximation. It's the best simple method there is, and it's still roughly ±5% — we'd rather tell you that than pretend four decimal places.
What to do with your number
Is salt actually cheaper for your pool? → ·What heating your pool really costs → ·What a variable-speed pump saves → ·Which robot batteries you can replace → ·Salt cell cost per year, by model →
FAQ
How many gallons is a 16x32 pool?
A 16 × 32 ft rectangular in-ground pool with a typical 3.5 ft shallow end and 6.5 ft deep end (5 ft average depth) holds about 19,150 gallons. One depth everywhere at 4 ft would be about 15,320 gallons. Use the calculator above with your real depths — the deep end swings the number more than most people expect.
How many gallons is a 24-foot round pool?
A 24 ft round above-ground pool with a 52-inch wall holds about 13,536 gallons — the wall height isn't the water depth (a 52" wall holds roughly 48" / 4 ft of water). At a 54" wall (~4.25 ft of water) it's about 14,382 gallons.
How do I calculate my pool’s average depth?
If the bottom slopes evenly from shallow to deep, average depth = (shallow + deep) ÷ 2. But a diving pool isn’t an even slope — it’s a shallow flat section, a short slope, and a deep hopper, and most of the length is shallow. The simple average overstates that pool’s volume by 10–15%. Our calculator’s "diving pool" mode weights each section by its share of the pool’s length instead.
Why does pool volume matter?
Every dose is per-gallon: chlorine, shock, acid, stabilizer, and the salt for a salt system all scale with volume. It also sets your equipment sizes — pump flow for a full turnover, heater BTUs, and the salt-cell rating (buy a cell rated for about twice your gallons; it runs at lower output and lasts longer). Get the volume wrong and everything downstream is wrong with it.
Are oval pool calculators accurate?
Only if they use the right oval. A true ellipse and a rounded-rectangle "stadium" oval (straight sides, rounded ends — what most above-ground oval pools actually are) differ by up to ~12% for the same length and width. Most calculators silently use one formula for both. Ours asks which oval you have.