Pool volume calculator
Pick your pool's shape, enter its size in feet, and this tells you roughly how many gallons it holds. You'll need that number for almost every chemical, from salt to shock.
How many gallons is my pool?
Next step for salt pools: the pool salt calculator has this same volume calculator built in and turns gallons into pounds of salt.
How to measure your pool
- Length and width: measure the inside of the pool at the waterline, wall to wall. For a round pool, measure straight across through the middle; that's the diameter.
- Depth: measure the water, not the wall. On a sloped in-ground pool, take the depth at the shallow end and the deep end. If the floor is flat, you only need one figure.
- Feet and inches: type them as you read them off the tape, like 3 9 for 3 ft 9 in. Decimals work too (3.75).
The formulas
Every formula does the same three things: work out the water's surface area, multiply by the average depth to get cubic feet, then convert to gallons.
Average depth = (shallow depth + deep depth) ÷ 2
A US gallon is 231 cubic inches and a cubic foot is 1,728 cubic inches, so one cubic foot of water is 1,728 ÷ 231 = 7.48 gallons. That's the number behind every pool volume formula.
Rectangle
Gallons = length × width × average depth × 7.48
Example: a 32 by 16 ft pool, 3 ft 6 in at the shallow end and 8 ft at the deep end. The average depth is (3.5 + 8) ÷ 2 = 5.75 ft. So 32 × 16 × 5.75 = 2,944 cubic feet, and 2,944 × 7.48 = about 22,020 gallons.
Round
Gallons = diameter × diameter × average depth × 5.875
The 5.875 is pi ÷ 4 × 7.48, which turns a circle's diameter into area and cubic feet into gallons in one go. You'll often see it rounded to 5.9.
Example: a 24 ft round above-ground pool with 4 ft of water. 24 × 24 × 4 × 5.875 = about 13,540 gallons. The City of Akron's pool table, which uses 5.9, lists a 24 ft round pool with a 52-inch wall at about 13,594 gallons, so the two agree to within half a percent.
Oval with straight sides
Most oval above-ground pools are a rectangle with a half circle on each end. Treat it as exactly that:
Area = (length − width) × width + width × width × 0.785
Gallons = area × average depth × 7.48
Pentair's IntelliChlor manual uses a shortcut for ovals instead: length × width × average depth × 6.7. For a typical oval twice as long as it is wide, that lands within half a percent of the method above.
Example: a 30 by 15 ft oval with 4 ft of water. The straight middle is (30 − 15) × 15 = 225 sq ft, and the two round ends make one 15 ft circle, 15 × 15 × 0.785 = 176.7 sq ft. Together that's 401.7 sq ft. Then 401.7 × 4 × 7.48 = about 12,020 gallons.
Oval with no straight sides
Gallons = length × width × average depth × 5.875
The same 30 by 15 ft size as a smooth egg shape holds less: 30 × 15 × 4 × 5.875 = about 10,580 gallons. That gap is why the calculator asks which kind of oval you have.
How close is close enough?
For day-to-day chemicals, an estimate within 5 to 10% is fine, because you'll test the water afterward and adjust. Where it matters more is salt, which you can't easily take back out. If your pool's manual or the installer's paperwork gives a capacity, compare it with the calculator's answer. If they disagree by a lot, trust the measurement you just took over a brochure figure, and add chemicals in stages.
Dosing: once you know your gallons, follow the dose on the product label for that volume. Add chemicals one at a time, never mix them together, and keep them away from children. The CDC's pool chemical safety page covers storage and handling.
Common questions
Should I measure the wall height or the water depth?
The water depth. Above-ground pools are rarely filled to the top of the wall, and an in-ground pool's water usually sits partway up the skimmer opening. Measure from the water surface to the floor.
My pool has a hopper or a sudden drop. Is the average still right?
It's close, not exact. The average assumes the floor slopes evenly from shallow to deep. For a pool with a steep drop-off, split it into two rectangles (the shallow section and the deep section), work out each one with its own depth, and add them together.
How do I work out a kidney or freeform pool?
Break it into shapes the calculator knows. A kidney pool is roughly two circles of different sizes, or a rectangle with rounded ends. Work out each piece and add them up. It won't be perfect, but it'll be well within the margin that matters for dosing chemicals.
Why is my answer a little lower than another calculator's?
Many pool calculators round the factor for round and oval pools up to 5.9. The exact figure is 5.875 (pi divided by 4, times 7.48 gallons per cubic foot). The difference is under half a percent.
Is anything I type saved or sent?
No. The calculator runs in your browser and works offline once the page has loaded. Nothing is sent to us.
Sources
- 1 cubic foot = 7.48 gallons: California State Water Resources Control Board, Equivalents and Formulas, and University of California Cooperative Extension, Understanding Water Units, read November 10, 2026.
- Industry formulas (7.5, 5.9 and 6.7 factors): Pentair, IntelliChlor IC15 Installation and User's Guide, and City of Akron, How to calculate the gallons in a swimming pool, read November 10, 2026.
- US gallon = 231 cubic inches: NIST Handbook 44, Appendix C (General Tables of Units of Measurement), 2026 edition, nist.gov, checked November 10, 2026.
- Pool chemical handling: CDC, Pool Chemical Safety, checked November 10, 2026.
- Areas of a rectangle, circle and ellipse are standard geometry. Worked examples were checked by hand and by the site's automated tests.