The short answer
To find pool gallons, multiply length × width × average depth in feet, then multiply by 7.48 (the gallons in one cubic foot). Average depth is the shallow end plus the deep end, divided by 2. A 16 × 32 ft pool that goes from 3.5 to 6 ft deep holds about 18,190 gallons. For round pools, multiply diameter × diameter × average depth × 5.875.
Pool volume formulas
Work out the volume in cubic feet, then multiply by 7.48 to get US gallons (or work in metres and multiply by 1,000 for litres).
| Pool shape | Volume in cubic feet |
|---|---|
| Rectangle | length × width × average depth |
| Round | 3.1416 × (diameter ÷ 2)² × average depth |
| Oval | 3.1416 × (length ÷ 2) × (width ÷ 2) × average depth |
| Kidney | 0.45 × (width A + width B) × length × average depth |
For kidney pools, A and B are the widths across the two rounded ends. Pool manufacturers often round the gallon factors to 7.5 for rectangles and 5.9 for round and oval pools; this calculator uses the exact values.
Worked example
A 16 × 32 ft rectangular pool, 3.5 ft at the shallow end and 6 ft at the deep end:
- Average depth: (3.5 + 6) ÷ 2 = 4.75 ft
- Volume: 16 × 32 × 4.75 = 2,432 cubic feet
- Gallons: 2,432 × 7.48 = about 18,190 gallons (68,870 litres)
Gallons for common pool sizes
| Pool | Average depth | Gallons | Litres |
|---|---|---|---|
| 12 × 24 ft rectangle | 4.5 ft | 9,695 | 36,699 |
| 16 × 32 ft rectangle | 4.75 ft | 18,193 | 68,867 |
| 18 × 36 ft rectangle | 5 ft | 24,237 | 91,747 |
| 20 × 40 ft rectangle | 5.5 ft | 32,914 | 124,594 |
| 15 ft round | 4 ft | 5,288 | 20,016 |
| 18 ft round | 4 ft | 7,614 | 28,823 |
| 24 ft round | 4 ft | 13,536 | 51,241 |
| 27 ft round | 4 ft | 17,132 | 64,852 |
Tips
- Measure the water, not the pool. Water usually sits a few inches below the top of the wall or the coping.
- For pools with a sloping middle, measure several depths along the length and average them for a closer figure.
- Write the number down. You will use it every time you add chemicals or salt. The pool salt calculator needs it next.
Frequently asked questions
How do I find the average depth of my pool?
Add the depth of the shallow end to the depth of the deep end and divide by 2. A pool that is 3.5 ft at one end and 6 ft at the other has an average depth of 4.75 ft. For above-ground pools, use the water depth, not the wall height.
How many gallons are in a cubic foot of water?
One cubic foot holds 7.48 US gallons, and one cubic metre holds 1,000 litres.
How many gallons is a 24 ft round pool?
A 24 ft round pool with 4 ft of water holds about 13,540 gallons. At 4.5 ft of water it holds about 15,230 gallons.
How long does it take to fill a pool with a garden hose?
A typical garden hose delivers 5 to 10 gallons per minute. At 9 gallons per minute, an 18,000-gallon pool takes about 33 hours to fill.
Why do I need to know my pool volume?
Chemical doses, salt levels and pump sizing are all based on volume. Getting it wrong is the most common reason pool water is hard to balance.
Sources
Related calculators
About this calculator. Every formula on this page is tested against worked examples from the sources above before publishing. Results are estimates for planning; confirm with your supplier or local code.
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