How to calculate pool volume
Find the area of the water surface, multiply by the average depth to get cubic feet, then convert to gallons. One cubic foot holds about 7.48 US gallons.
average depth = (shallow depth + deep depth) ÷ 2
gallons = surface area (sq ft) × average depth (ft) × 7.48
| Shape | Surface area | Shortcut in gallons |
|---|---|---|
| Rectangle | length × width | L × W × avg depth × 7.48 |
| Round | 3.1416 × (diameter ÷ 2)² | diameter² × avg depth × 5.9 |
| Oval | 3.1416 × (length ÷ 2) × (width ÷ 2) | L × W × avg depth × 5.9 |
In metric, multiply the surface area in m² by the average depth in meters to get cubic meters. Each cubic meter is 1,000 liters.
Worked example
A 32 × 16 ft rectangular pool with 3.5 ft of water at the shallow end and 6 ft at the deep end has an average depth of 4.75 ft. Its surface is 512 sq ft, so it holds 512 × 4.75 = 2,432 cu ft, or 2,432 × 7.48 = 18,191 gallons. In metric that is 68.9 m³, or about 68,866 liters. Each inch of depth holds about 319 gallons.
Round above-ground pools at 4 ft of water
| Diameter | Gallons | Liters | Per inch of depth |
|---|---|---|---|
| 12 ft | 3,384 | 12,810 | 70 gal |
| 15 ft | 5,287 | 20,016 | 110 gal |
| 18 ft | 7,614 | 28,823 | 159 gal |
| 21 ft | 10,363 | 39,231 | 216 gal |
| 24 ft | 13,535 | 51,241 | 282 gal |
| 27 ft | 17,131 | 64,852 | 357 gal |
The water level in an above-ground pool sits below the top of the wall, so measure the water itself rather than using the wall height printed on the box.
Measuring tips
- Measure the inside of the pool at the waterline, not the outside of the coping or deck.
- For depth, measure from the water surface to the floor at the shallowest and deepest points. A pole with tape marks works well.
- If the floor has a steep hopper or a long flat deep section, the simple average can be off. Split the pool into a shallow part and a deep part, calculate each and add them.
- Kidney and free-form pools: treat them as an oval of the same overall length and average width, or split them into simpler shapes.
Unit conversions
| From | To | Multiply by |
|---|---|---|
| Cubic feet | US gallons | 7.48 |
| US gallons | Liters | 3.785 |
| Cubic meters | Liters | 1,000 |
| Cubic meters | US gallons | 264.2 |
How long will it take to fill?
Time how long your hose takes to fill a 5-gallon bucket. If it takes 30 seconds, the hose delivers 10 gallons per minute, and the 18,191-gallon pool in the example takes about 1,819 minutes, or roughly 30 hours. Pressure and hose size change the flow, so measure your own. For large fills, ask your water utility about delivery or any sewer-charge credit for pool filling.
Why the volume matters
Chemical labels, heaters and pumps are all sized by volume. Most pool chemical directions give a dose per 10,000 gallons or per set number of liters. Use your volume with the product label and a reliable test kit. Never guess doses, never mix chemicals together, and store them as the label directs.
Closing the pool for winter? The water-per-inch figure tells you how much you remove when you lower the level. See how much to lower pool water for winter.
Frequently asked questions
How many gallons are in a 24 ft round pool?
With 4 ft of water, a 24 ft round pool holds about 13,535 gallons, or roughly 51,241 liters.
How do I find the average depth of a pool?
Add the depth at the shallow end to the depth at the deep end and divide by 2. A pool 3.5 ft at one end and 6 ft at the other averages 4.75 ft.
How many gallons are in a cubic foot?
About 7.48 US gallons. A cubic meter holds 1,000 liters.
Does this calculator give chemical doses?
No. It gives the volume you need to read chemical labels correctly. Follow the product directions and test the water.