Pool volume in gallons is surface area × average depth × 7.5 for rectangular pools, and diameter × diameter × average depth × 5.9 for round pools. Average depth is the shallow and deep end added and divided by two. A 16 × 32 ft pool averaging 5 ft holds about 19,200 gallons. Every pump, filter, heater, salt cell and chemical dose is sized from this number.
Almost every pool decision starts with one number: how many gallons it holds.
Formulas
| Shape | Gallons |
|---|---|
| Rectangle | Length × width × average depth × 7.5 |
| Round | Diameter × diameter × average depth × 5.9 |
| Oval | Length × width × average depth × 5.9 |
| Freeform | Approximate with rectangles and circles, or use the builder’s figure |
All measurements in feet. One cubic foot holds about 7.48 gallons.
Average depth
Average depth = (shallow end + deep end) ÷ 2. For a pool with a long shallow area and a small deep end, split it into sections and add them.
Examples
| Pool | Math | Gallons |
|---|---|---|
| 12 × 24 ft, 4.5 ft avg | 12 × 24 × 4.5 × 7.5 | 9,720 |
| 16 × 32 ft, 5 ft avg | 16 × 32 × 5 × 7.5 | 19,200 |
| 20 × 40 ft, 5.5 ft avg | 20 × 40 × 5.5 × 7.5 | 33,000 |
| 18 ft round, 4 ft | 18 × 18 × 4 × 5.9 | 7,646 |
| 24 ft round, 4 ft | 24 × 24 × 4 × 5.9 | 13,594 |
What it sizes
- Pump. Turnover rate in gallons per minute; see variable-speed pump sizing.
- Filter. Must handle the pump’s flow; see sand vs cartridge vs DE.
- Salt cell. Rated in gallons; buy above your volume; see saltwater systems.
- Heater. Sized with surface area and climate; see heat pump vs gas.
- Chemicals. Every dose chart is per 10,000 gallons.
Browse pumps and filters.
Common questions
How many gallons is a 16 x 32 pool?
About 19,200 gallons at an average depth of 5 feet (16 × 32 × 5 × 7.5).
How do I calculate gallons for a round above-ground pool?
Diameter × diameter × average depth × 5.9. A 24 ft round pool at 4 ft deep holds about 13,600 gallons.
How do I find average depth?
Add the shallow-end and deep-end depths and divide by two. Measure water depth, not wall height.
Why does pool volume matter?
Pump turnover, filter size, heater BTUs, salt cell ratings and every chemical dose are calculated from it.