Why pool volume matters
Almost every number in pool care depends on the volume: chemical doses, the amount of salt for a chlorine generator, pump and filter sizing, and the time and water needed to fill it. This calculator finds the volume of rectangular, round and oval pools with a sloped bottom, in gallons, cubic feet and liters.
The formulas
- Surface area:
- Rectangle: length × width.
- Round: 3.14 × (diameter ÷ 2)².
- Oval: (length − width) × width + 3.14 × (width ÷ 2)², a rectangle with two half-circle ends.
- Average depth = (shallow end + deep end) ÷ 2.
- Volume (cu ft) = surface area × average depth.
- Gallons = cubic feet × 7.48.
Worked example: a 16 × 32 ft in-ground pool
The shallow end is 3.5 ft deep and the deep end 6 ft.
- Surface: 32 × 16 = 512 sq ft.
- Average depth: (3.5 + 6) ÷ 2 = 4.75 ft.
- Volume: 512 × 4.75 = 2,432 cubic feet.
- Gallons: 2,432 × 7.48 = 18,193 gallons, or about 68,900 liters.
- With a hose at 9 gal/min, filling takes about 34 hours.
- A salt system at 3,200 ppm needs about 486 lb of salt.
- To turn the water over in 8 hours, the pump must move about 38 gal/min.
Volume by deep end depth
| Deep end | Gallons | Fill time | Salt at 3,200 ppm |
|---|---|---|---|
| 3.5 ft (flat) | 13,405 | 24.8 h | 358 lb |
| 5 ft | 16,278 | 30.1 h | 434 lb |
| 6 ft | 18,193 | 33.7 h | 486 lb |
| 8 ft | 22,023 | 40.8 h | 588 lb |
Irregular shapes
For a kidney or freeform pool, split it into simple shapes, calculate each one and add them. Or use the oval shape with the longest length and the average width for a quick estimate. Hoppers and steep slopes change the average depth: measure depth at several points and average them.
Using the volume
- Chemicals: dosing charts are written per 10,000 gallons. For 18,193 gallons, multiply the dose by 1.82.
- Salt: the salt figure assumes fresh water with no salt. For a top-up, use the difference between the target and your test result.
- Pump: most codes and manufacturers aim for a full turnover in 6 to 8 hours. A variable-speed pump can run longer at low speed and use far less electricity.
- Filling: ask your water utility about pool-fill programs or sewer credits, since pool water does not go down the drain. Large pools are often filled faster and cheaper by a water truck.
Above-ground pools
Above-ground pools have a flat bottom, so enter the same depth for both ends: the water depth, not the wall height. A 24 ft round pool with 4 ft of water holds about 13,500 gallons.