Pool Volume Calculator — gallons and litres
Gallons from the pool's shape and its shallow and deep ends, with the exact 231 in³ gallon, in gallons, litres and cubic metres.
How many gallons a pool holds, from its shape and the shallow and deep ends, with the exact gallon — the number every chemical dose and every fill-up starts from.
Quick answer: gallons in common pool sizes
| Pool | Depth | US gallons | Litres |
|---|---|---|---|
| Rectangle 12 × 24 ft | 4 ft | 8,618 | 32,621 |
| Rectangle 16 × 32 ft | 3.5 to 8 ft | 22,023 | 83,365 |
| Rectangle 18 × 36 ft | 3.5 to 8 ft | 27,872 | 105,509 |
| Rectangle 20 × 40 ft | 3.5 to 8 ft | 34,410 | 130,257 |
| Round 18 ft | 4 ft | 7,614 | 28,823 |
| Round 24 ft | 4 ft | 13,536 | 51,241 |
| Oval 15 × 30 ft | 4 ft | 10,575 | 40,032 |
Surface area × average depth × 7.480519 gallons per cubic foot. The sloped pools assume a straight slope from shallow to deep end; a shelf or hopper bottom changes the number, so measure several depths and average them.
| Surface area | — |
|---|---|
| Average depth | — |
| Volume | — |
| US gallons | — |
| Litres | — |
Average depth is the whole trick. A pool with a shallow end and a deep end and a straight slope between them holds surface area times the average of the two depths. A 30 × 15 pool from 3½ to 8 feet averages 5¾ feet: 2,587 cubic feet, about 19,400 gallons. A pool with a flat shallow shelf and a sudden drop holds more than the average says, and one with a hopper bottom holds less; for those, measure the depth at several points and average them, then enter that as both ends.
Gallons are 231 cubic inches, exactly. That makes 7.480519 US gallons to the cubic foot, and the page uses that figure rather than 7.5. On 20,000 gallons the rounded factor is off by 50 gallons, which is a few ounces of chlorine either way. Small, but there is no reason to be wrong.
Oval is an ellipse, and kidney pools are not. The oval here is π/4 × length × width, which is right for a true oval. A kidney or freeform pool has no single factor, and this page does not guess one. Split the surface into rectangles and rounds, run the page once per piece at the same depths, and add the results.
The volume is for the chemistry. CDC recommends a pH of 7.0 to 7.8 and free chlorine of at least 1 ppm in a pool, at least 2 ppm in a pool that uses cyanuric acid (stabilizer), and at least 3 ppm in a hot tub, where it recommends no cyanuric acid at all. It says to test chlorine and pH at least twice a day. Those are concentrations; the gallons on this page are what turn them into an amount.
One ppm is a weight of chlorine, and the gallons set it. A part per million in water is a milligram per litre, so raising 10,000 gallons (37,854 L) by 1 ppm takes 37.9 g of available chlorine: 3.79 g for every 1,000 gallons. The 30 × 15 ft pool above, about 19,400 gallons, needs about 73 g per ppm; a 400-gallon hot tub needs 1.5 g. How much product that is depends on its strength, which is printed on the label, and the label's directions are the ones to follow.
A volume ten percent off is a dose ten percent off. That is the reason this page uses 7.480519 gallons per cubic foot rather than 7.5, and the reason a shelf or a hopper bottom should be averaged from several depths: an average taken from the two ends of a pool with a hopper overstates the water, and the chlorine follows the overstatement.
What I check on a job
Measure the water, not the pool. Before I trust this figure I check what the dimensions were measured to. Drawings and sales sheets usually give the shell or the coping, but the water sits inside the finished wall and below the coping, so a length taken off a plan and a depth taken from the deck both push the number high. I measure the water itself: inside face to inside face at the surface, and depth from the waterline down. A round above-ground pool sold by its nominal size is the same trap, and its wall height is not its water depth. Then I take out what is not water. Built-in steps, a bench along one wall or a raised ledge are solid volume that the formula counts as water, and on a small pool they matter. The number I pass to whoever doses or fills the pool is the measured one, with a note of what it leaves out.
Rectangle = L × W; round = π (d ÷ 2)²; oval = π/4 × L × W. Volume = area × (shallow + deep) ÷ 2. 1 US gallon = 231 in³ (exact), so 1 ft³ = 7.480519 gal = 28.316846592 L.
Worked example
A 30 × 15 ft pool, 3½ ft at the shallow end and 8 ft at the deep end: how many gallons?
- Surface 450 ft²; average depth (3.5 + 8) ÷ 2 = 5.75 ft.
- 450 × 5.75 = 2,587.5 ft³.
- × 7.480519 = 19,356 US gallons (73.3 m³, 73,270 L).
About 19,400 gallons. A 24 ft round pool 4½ ft deep is 2,036 ft³, 15,228 gallons. The gallon is 231 in³ exactly; 7.5 per cubic foot is close and wrong by 50 gallons here.
9 values on this page were driven in a browser and compared with independently derived figures on 2026-10-29 (2808 values across 228 calculators site-wide).
Questions
How do you calculate pool gallons?
Surface area × average depth × 7.480519. A 30 × 15 ft pool from 3½ to 8 ft holds 2,587 ft³, about 19,400 gallons.
How many gallons in a cubic foot?
7.480519, because a US gallon is exactly 231 cubic inches (1,728 ÷ 231).
How many gallons is a 30 × 15 pool from 3½ to 8 feet?
About 19,400 gallons: the average depth is 5¾ ft, so 450 ft² × 5.75 = 2,587 ft³, times 7.480519 gallons per cubic foot. That holds for a straight slope between the two ends.
What if the pool has a shallow shelf or a hopper bottom?
Then the two-end average is wrong: a flat shelf with a sudden drop holds more than it says and a hopper holds less. Measure the depth at several points, average them, and enter that figure as both the shallow and the deep end.