Chemical doses, heater sizing, pump turnover and the water bill all start from one number: how many gallons the pool holds. Volume is surface area × average depth, and every cubic foot holds 7.48 US gallons (a US gallon is defined as 231 in³). This pool volume calculator handles rectangular, round and oval pools, averages the shallow and deep ends of a sloped floor, and gives the result in US gallons, liters and cubic feet. It also tells you how long the fill will take at your hose's flow rate, and how many gallons each inch of water level represents, which helps when topping up or draining.
Planning the deck or patio around it? Try the paver calculator. The rainwater harvesting calculator estimates what a roof could collect toward top-ups.
How to use the pool volume calculator
- Choose the shape. "Oval" here means the common above-ground shape with straight sides and semicircular ends.
- Measure the inside length and width, or the diameter, of the water surface.
- Measure the water depth, not the wall height, at the shallow and deep ends. If the floor slopes evenly, the average depth is accurate.
- Optionally enter your hose flow rate in gallons per minute to estimate the fill time.
Formula
The 7.4805 factor follows from 1 ft³ = 1,728 in³ and 1 US gallon = 231 in³ (NIST). Pools with a hopper or a sharp break between shallow and deep sections hold a little different from the simple average; split them into sections if you need precision.
Worked example
A 32 × 16 ft rectangular in-ground pool, 3½ ft shallow end and 6 ft deep end, filled with an 8 gal/min hose.
- Area: 512 ft². Average depth: (3.5 + 6) ÷ 2 = 4.75 ft.
- Volume: 512 × 4.75 = 2,432 ft³.
- Gallons: 2,432 × 7.4805 = 18,193 US gallons (68,867 L).
- Fill time: 18,193 ÷ 480 = about 37.9 hours.
- Each inch of level: 512 ÷ 12 × 7.4805 = 319 gal.
A 24 ft round above-ground pool with 4 ft of water: π × 12² × 4 = 1,809.6 ft³ = 13,536 gallons.
Gallons in common above-ground pools (4 ft of water)
| Pool | Gallons |
|---|---|
| 12 ft round | 3,384 |
| 15 ft round | 5,288 |
| 18 ft round | 7,614 |
| 21 ft round | 10,364 |
| 24 ft round | 13,536 |
| 27 ft round | 17,132 |
| 15 × 30 ft oval | 12,020 |
| 18 × 33 ft oval | 15,693 |
Calculated with this tool. Many pools are filled a few inches below the top of the wall, so the real volume is usually a little less than the wall height suggests.
Using the volume
Pool chemical labels give doses per 10,000 gallons (or per cubic meter), so an accurate volume is the first step in balancing water. Always follow the product label and test the water before and after adding chemicals. Pump and filter sizing is based on turnover, the time to circulate the whole volume once, so divide the gallons by the pump's flow in gal/min and by 60 to get turnover hours. Local codes and health departments set turnover requirements for public pools. For residential pools, follow the equipment maker's guidance. The Pool & Hot Tub Alliance publishes industry standards for residential pools and spas.
Caveats and assumptions
- Assumes vertical walls and an evenly sloping floor; freeform, kidney or hopper-bottom pools are approximations.
- Use water depth, not wall height, for the volume.
- US gallons are used; one imperial gallon is about 1.2 US gallons.
- Fill time ignores changes in water pressure, and some water utilities limit or price pool fills; check before filling.
Frequently asked questions
How many gallons are in a 24 ft round pool?
With 4 ft of water, π × 12² × 4 × 7.48 = about 13,536 gallons. At 52 in of water, about 14,664 gallons.
How do I calculate pool gallons?
Multiply surface area by average depth to get cubic feet, then multiply by 7.48 for US gallons.
How many gallons in a 16 × 32 pool?
With a 3½–6 ft floor (4.75 ft average), about 18,200 gallons.
How long does it take to fill a pool with a hose?
Divide the gallons by your hose flow in gal/min and by 60. At 8 gal/min, an 18,000-gallon pool takes about 37–38 hours.
How many liters are in a cubic foot?
About 28.32 liters, and a cubic meter is 1,000 liters.
Sources
- NIST Handbook 44, Appendix C — General Tables of Units of Measurement — 1 US gallon = 231 in³
- NIST SP 811, Appendix B — conversion factors — cubic foot to liter
- Pool & Hot Tub Alliance (PHTA) — Standards — industry standards for residential pools and spas
This calculator gives estimates for planning and education. Check measurements, local codes, supplier specs and your school's official policy before relying on a result. See our disclaimer and how we build and check calculators.