On this page
How to calculate pool volume
Get the volume in cubic feet from the pool's shape and average depth, then multiply by 7.48: a US gallon is 231 cubic inches, so a cubic foot holds 7.48 gallons.
| Pool shape | Cubic feet | Gallons |
|---|---|---|
| Rectangle | L × W × avg depth | cu ft × 7.48 |
| Round | π × (diameter ÷ 2)² × depth | ≈ 5.9 × diameter² × depth |
| Oval | π ÷ 4 × L × W × avg depth | ≈ 5.9 × L × W × depth |
| Kidney | 0.45 × (A + B) × L × avg depth | cu ft × 7.48 |
Average depth is (shallow + deep) ÷ 2. The kidney formula is the usual industry approximation, where A and B are the widths of the two lobes.
Gallons in common pool sizes
| Pool | Gallons | Liters |
|---|---|---|
| Rectangle 12 × 24 ft, 3.5–6 ft deep | 10,233 | 38,737 |
| Rectangle 16 × 32 ft, 3.5–8 ft deep | 22,023 | 83,365 |
| Rectangle 20 × 40 ft, 4–8 ft deep | 35,906 | 135,921 |
| Round 15 ft, 4 ft of water | 5,288 | 20,016 |
| Round 18 ft, 4 ft of water | 7,614 | 28,823 |
| Round 24 ft, 4.5 ft of water | 15,228 | 57,646 |
| Oval 15 × 30 ft, 4 ft of water | 10,575 | 40,032 |
Measure the water, not the wall
Use the water depth, not the wall height. On an above-ground pool the water usually sits a few inches below the top of the wall.
Fill time and water cost
Enter your hose or tap flow to see how long filling takes. To measure it, time how many seconds a 5 gallon bucket takes: 5 ÷ seconds × 60 = gallons per minute. Add your water rate per 1,000 gallons from the utility bill for the fill cost.
Frequently asked questions
How do I calculate pool gallons?
Find the volume in cubic feet (length × width × average depth for a rectangle), then multiply by 7.48, the number of US gallons in a cubic foot. A 16 × 32 ft pool averaging 5.75 ft deep holds 2,944 cu ft × 7.48 = about 22,020 gallons.
How do I find the average depth of a pool?
Add the shallow-end depth and the deep-end depth and divide by 2. For pools with a long flat shallow section and a short deep hopper, measure in a few places and average them for a closer figure.
How long does it take to fill a pool?
Gallons ÷ flow rate. A 20,000 gallon pool filled by a hose at 10 gallons per minute takes 2,000 minutes: about 33 hours. Time how long your hose takes to fill a 5 gallon bucket to get your real flow.
Why does pool volume matter?
Chemical labels give doses per so many gallons, and pumps, filters and heaters are sized by volume. A wrong gallon figure means every dose is wrong.
