How to use the pool volume calculator
Pick your pool's shape and enter its inside dimensions. If the floor slopes, enter the water depth at the shallow end and the deep end; the calculator averages them. For an above-ground pool, choose Same depth throughout and enter the actual water depth, usually a few inches less than the wall height.
Knowing the volume is the first step for dosing chlorine, salt and shock, all of which are measured per 10,000 gallons. A rough guess is worse than you'd think: overestimate by 20% and every dose is 20% too strong.
The formulas
average depth = (shallow + deep) ÷ 2
rectangle: length × width × average depth × 7.48
round: 3.1416 × (diameter ÷ 2)² × depth × 7.48
oval: 3.1416 × (length ÷ 2) × (width ÷ 2) × depth × 7.48
kidney: (A + B) × length × 0.45 × depth × 7.48
7.48 is the number of US gallons in a cubic foot (more precisely 7.48052). For litres, multiply cubic feet by 28.32.
Worked example: a 32 × 16 ft in-ground pool, 3½ to 8 ft deep
- Average depth: (3.5 + 8) ÷ 2 = 5.75 ft.
- Volume: 32 × 16 × 5.75 = 2,944 ft³.
- Gallons: 2,944 × 7.48052 = 22,023 US gallons, about 83,400 litres.
- Filling at 8 gallons a minute takes 2,753 minutes, almost 46 hours.
Typical pool sizes
| Pool | Water depth | Approx. gallons |
|---|---|---|
| 15 ft round above-ground | 4 ft | 5,300 |
| 18 ft round above-ground | 4 ft | 7,600 |
| 24 ft round above-ground | 4 ft | 13,500 |
| 16 × 32 ft in-ground | 3½-8 ft | 22,000 |
| 20 × 40 ft in-ground | 3½-8 ft | 34,400 |
Measuring tips
- Measure inside the walls, at the water line.
- Deep end: use a weighted tape or a pole, measured at the deepest point. Use the main slope, not the very bottom of a small hopper.
- Freeform pools: break the surface into a rectangle plus semicircles, or use the kidney formula as a starting point. For chemical dosing, a 5 to 10% estimate is fine; test the water and adjust.
- Check your water meter. Read it before and after filling. That's the most accurate volume you'll ever get.
Questions people ask
How do I calculate how many gallons are in my pool?
Multiply the surface area in square feet by the average water depth in feet, then by 7.48 (gallons in a cubic foot). For a rectangle that's length × width × average depth × 7.48.
How many gallons is a 24 ft round above-ground pool?
With water 4 ft deep, about 13,500 US gallons: 3.1416 × 12 × 12 × 4 = 1,810 cubic feet, × 7.48 = 13,536 gallons. At 4.5 ft deep it's about 15,200.
How do I find the average depth of a pool?
Add the shallow-end depth and the deep-end depth and divide by 2. A pool 3½ ft at one end and 8 ft at the other averages 5.75 ft. Use water depth, not wall height: most pools are filled a few inches below the top.
How do you calculate the volume of a kidney-shaped pool?
The pool industry uses an approximation: (A + B) × length × 0.45 × average depth × 7.48, where A and B are the widths across the two lobes. It's an estimate; the true shape varies by builder.
Why do I need to know my pool's volume?
Chemical doses (chlorine, salt, shock, pH adjusters) are all given per 10,000 gallons. Getting the volume wrong by 20% means every dose is wrong by 20%.
How long does it take to fill a pool with a garden hose?
A typical garden hose delivers somewhere around 5 to 10 gallons a minute. At 8 gpm, a 20,000 gallon pool takes about 42 hours. Measure your own flow by timing how long it takes to fill a 5 gallon bucket.
Sources and assumptions
- NIST Handbook 44, Appendix C: 1 ft³ = 7.48052 US gallons
- The kidney factor, 0.45 × (A + B) × L, is the approximation pool retailers publish. It is an estimate; freeform shapes vary by builder.
- Average depth assumes a straight slope from shallow to deep. Pools with a long flat shallow section and a short steep hopper hold slightly more.
Last reviewed 27 October 2026. Every formula on this page is checked against the worked example above in our automated tests. Found a problem? Tell us.