How to use the pool volume calculator
- Pick the shape closest to your pool.
- Measure inside the pool walls: length and width, or diameter.
- Measure water depth, not wall height, at the shallow and deep ends. Untick the box for a pool with one depth.
- Read gallons, litres and fill time.
Pool volume formulas
Average depth = (shallow + deep) ÷ 2
Rectangle: length × width × average depth × 7.48
Round: 3.14 × radius² × depth × 7.48
Oval: 0.785 × length × width × average depth × 7.48
Kidney: 0.45 × (width A + width B) × length × average depth × 7.48
Worked example
A 16 × 32 ft in-ground pool, 3 1/2 to 8 ft deep
- Average depth = (3.5 + 8) ÷ 2 = 5.75 ft.
- 16 × 32 × 5.75 = 2,944 cu ft.
- 2,944 × 7.48 = 22,023 gallons (83,365 litres).
- Each inch of water is about 319 gallons.
Common pool sizes
| Pool | Water depth | Gallons |
|---|---|---|
| 15 ft round above-ground | 4 ft | 5,288 |
| 18 ft round above-ground | 4 ft | 7,614 |
| 24 ft round above-ground | 4 ft | 13,536 |
| 12 × 24 ft oval | 4 ft | 6,768 |
| 16 × 32 ft rectangle | 3.5 to 8 ft | 22,023 |
| 20 × 40 ft rectangle | 3.5 to 8 ft | 34,410 |
Common mistakes to avoid
- Using wall height. Water usually sits 6 in or so below the top.
- Measuring outside the walls. Measure the water surface, inside to inside.
- Guessing the deep end. Use a weighted tape or pole; a foot off changes the volume a lot.
Frequently asked questions
How do I calculate pool gallons?
Find the surface area, multiply by the average depth to get cubic feet, then multiply by 7.48. A 16 × 32 ft pool, 3.5 ft to 8 ft deep (5.75 ft average), holds 16 × 32 × 5.75 × 7.48 = about 22,000 gallons.
How many gallons in a round pool?
3.14 × radius² × depth × 7.48. A 24 ft round above-ground pool with 4 ft of water holds about 13,500 gallons.
How do I measure a kidney pool?
Measure the length, the width at the narrow end and the width at the wide end. A common approximation is 0.45 × (narrow width + wide width) × length × average depth.
Why do I need to know my pool volume?
Chemical doses, salt, heaters and pumps are all sized by gallons. Getting the volume wrong is the most common reason chemistry goes off.
How long does it take to fill a pool with a hose?
At 9 gallons per minute a 22,000 gallon pool takes about 41 hours (22,000 ÷ 9 ÷ 60). Check with your water utility before filling; some offer bulk water delivery.
How many gallons does an inch of water hold?
Surface area × 1/12 ft × 7.48. On a 16 × 32 ft pool, each inch is about 319 gallons, handy for tracking evaporation and leaks.