Why your pool's volume matters
Almost every pool job starts with knowing how many gallons you have. Chlorine, shock, pH adjusters and salt are all dosed per gallon, and pumps, filters and heaters are sized by volume. Guessing wrong means cloudy water, wasted chemicals or equipment that runs far longer than it should.
How the calculator works
It finds the surface area of your pool, multiplies it by the average water depth to get cubic feet, then converts to gallons using 7.48 gallons per cubic foot. The average depth is the shallow and deep ends added together and divided by two, which works well for pools with a steady slope.
The formulas
The kidney formula is a standard industry approximation. Free-form pools vary, so for an unusual shape you can split the pool into rectangles and circles and add them up.
Worked examples
Rectangular in-ground pool: 32 ft × 16 ft, 3 ft shallow end, 6 ft deep end. Average depth is 4.5 ft, so the volume is 32 × 16 × 4.5 = 2,304 cubic feet, or about 17,235 gallons (65,240 liters).
Round above-ground pool: 24 ft across with 4 ft of water. π × 12² × 4 = 1,810 cubic feet, or about 13,536 gallons.
Measuring tips
- Measure the water, not the walls. A 52 inch above-ground wall is usually filled to around 46–48 inches. Enter the water depth.
- Measure inside edges. Coping and decking make the outside dimensions larger than the water.
- Uneven floors. If your pool has a long flat shallow area and a sharp hopper, split it into two sections and add the volumes.
- Double-check with your water bill. If you filled from a metered supply, the bill shows the gallons used and is a good sanity check.
Using the number
Chemical labels usually give doses per 10,000 gallons. Divide your volume by 10,000 and multiply by the label dose. For pump sizing, many pool owners aim to turn over the full volume roughly once every 8 hours; divide your gallons by 480 to get the flow in gallons per minute that achieves that.
Frequently asked questions
How many gallons is a 24 ft round pool?
With 4 feet of water, a 24 foot round pool holds about 13,500 gallons. At 52 inches of water it holds about 14,700 gallons.
How many gallons is a 16 x 32 pool?
With a 3 ft shallow end and 6 ft deep end (4.5 ft average), a 16 by 32 foot pool holds about 17,200 gallons. With a flat 4 ft depth it holds about 15,300 gallons.
How many gallons are in a cubic foot?
One cubic foot holds about 7.48 US gallons, or 28.3 liters.
Why is the calculator's answer different from my pool builder's?
Builders often use exact plans that include steps, benches and curved walls, while this calculator uses standard shape formulas. Differences of 5 to 10% are normal.
How long will it take to fill my pool?
A typical garden hose delivers roughly 5 to 10 gallons a minute, so a 15,000 gallon pool can take 25 to 50 hours. Divide your gallons by your hose's flow rate to estimate.
Last reviewed November 2026. Spotted an error? Tell us.