How to calculate pool volume
The volume of a pool is its water surface area times its average depth. Measure the length and width at the water line and the depth from the floor to the water line, all in the same unit. In feet the result is in cubic feet; multiply by 7.48 to get US gallons. In meters the result is in cubic meters, and every cubic meter is 1,000 liters.
Example: a 16 by 32 ft pool that goes from 4 ft at the shallow end to 8 ft at the deep end has an average depth of 6 ft. 16 × 32 × 6 = 3,072 cubic feet, times 7.48 is about 22,980 gallons, or 86,989 liters.
Why a cubic foot is 7.48 gallons
The US gallon is a fixed volume. NIST Handbook 44, Appendix C (2026 edition) lists it as exactly 231 cubic inches. A cubic foot is 12 × 12 × 12 = 1,728 cubic inches, so it holds 1,728 ÷ 231 = 7.4805 gallons. With the inch defined as exactly 2.54 cm, a US gallon is 3.785411784 liters. The calculator uses these exact values and rounds only the result. The UK gallon is a different, larger unit; the volume converter handles both.
Oval, straight-sided and kidney pools
"Oval" means two different shapes. A true oval is an ellipse, curved all the way around, and its area is π ÷ 4 × length × width. Other oval pools have two straight sides and a half circle at each end. For those, pick Oval, straight sides: the area is a rectangle as long as the straight part plus one full circle as wide as the pool. With the same length and width, the straight-sided pool holds more water: a 15 by 30 ft pool with 52 inches of water holds about 11,457 gallons as an ellipse and 13,022 gallons with straight sides.
Kidney pools have no single formula, because no two curves are alike. The calculator uses the approximation 0.45 × (A + B) × length, where A is the width of the narrow end, B the width of the wide end and the length is measured along the longest line through the pool. As a check, the same outline without the inward curve, two round ends joined by straight sides, comes to between 0.45 and 0.47 × (A + B) × length for the sizes we tried, so 0.45 leaves room for the curve. A 30 ft kidney pool with ends of 10 and 15 ft and an average depth of 5 ft comes to about 12,623 gallons. For a free-form pool, split it into rectangles and circles, work out each part and add them up.
Average depth and sloped floors
When the floor slopes evenly from one end to the other, the average depth is the shallow end plus the deep end, divided by 2. If the floor is flat for a stretch and then drops more steeply, measure where the slope changes, work out each section with its own average depth and add the volumes, or take the depth at several points and average them. Measure to the water line, not the top of the wall: the water usually sits a little below the top, and only the water counts.
Gallons for example pool sizes
Rectangular pools with a shallow end of 3.5 ft and a deep end of 6 ft (average 4.75 ft):
| Pool | US gallons | Liters |
|---|---|---|
| 12 × 24 ft | 10,233 | 38,737 |
| 14 × 28 ft | 13,929 | 52,726 |
| 16 × 32 ft | 18,193 | 68,867 |
| 18 × 36 ft | 23,025 | 87,159 |
| 20 × 40 ft | 28,426 | 107,604 |
Round pools at two water depths:
| Diameter | 4 ft (48 in) of water | 52 in of water |
|---|---|---|
| 12 ft | 3,384 gal | 3,666 gal |
| 15 ft | 5,288 gal | 5,728 gal |
| 18 ft | 7,614 gal | 8,249 gal |
| 21 ft | 10,364 gal | 11,227 gal |
| 24 ft | 13,536 gal | 14,664 gal |
| 27 ft | 17,132 gal | 18,560 gal |
| 30 ft | 21,151 gal | 22,913 gal |
How long it takes to fill
Fill time is the volume divided by the flow rate. To find the flow rate of your hose, time how long it takes to fill a bucket of known size and divide: a 5 gallon bucket that is full after 30 seconds means 10 gallons per minute. At that rate the 16 by 32 ft pool above takes about 1 day 14 h. The calculator gives no chemical doses; follow the label of the product you use, which is where the volume comes in.
How to use the pool volume calculator
- 1Choose feet or meters and pick the shape of your pool: rectangle, round, oval, oval with straight sides, or kidney.
- 2Enter the length and width at the water line, or the diameter of a round pool. For a kidney, enter the widths of both ends.
- 3Enter the water depth, or the shallow and deep end for a sloped floor. Switch the depth to inches or centimeters if that is easier.
- 4Read the gallons, liters and cubic feet. Add a fill rate to see how long filling takes, then copy the result or the link.
Frequently asked questions
How many gallons is a 16 x 32 pool?
With a shallow end of 4 ft and a deep end of 8 ft, the average depth is 6 ft. 16 × 32 × 6 = 3,072 cubic feet, and at 7.48 gallons per cubic foot that is about 22,980 gallons, or 86,989 liters. With a constant 5 ft depth it would be about 19,150 gallons.
How many gallons is a 24 ft round pool?
It depends on the water depth, not the wall height. With 52 inches of water a 24 ft round pool holds about 14,664 gallons, with 48 inches about 13,536. Measure from the floor to the water line in the middle of the pool and enter that.
How many gallons are in a cubic foot of water?
About 7.48. NIST defines the US gallon as exactly 231 cubic inches, and a cubic foot has 12 × 12 × 12 = 1,728 cubic inches, so a cubic foot is 1,728 ÷ 231 = 7.4805 gallons. A cubic meter is 1,000 liters, or about 264.17 gallons.
How do I find the average depth of my pool?
For a floor that slopes evenly from the shallow end to the deep end, add the two depths and divide by 2: 3.5 ft and 8 ft give 5.75 ft. If the floor is flat for a long stretch and then drops steeply, split the pool into two parts at the drop, work out each with its own depth and add the volumes.
How long does it take to fill a pool?
Divide the volume by the flow rate of your hose or fill line. To measure it, time how long a 5 gallon bucket takes to fill: 30 seconds means 10 gallons per minute. At that rate a 22,980 gallon pool takes 2,298 minutes, about 1 day 14 h.
How accurate is the kidney-shaped pool estimate?
A kidney shape has no simple formula, so the calculator uses an approximation: 0.45 × (A + B) × length, with A and B the widths of the two rounded ends. Treat the result as an estimate. For a closer number, split the pool into simple shapes, like two circles and a rectangle, and add them up.