How Many Gallons in a Round Pool?
A round pool holds pi times the radius squared, times the average depth, times 7.48 for gallons. Here is the formula and a full chart for common above-ground round pools from 12 to 30 ft.
By the Calculate My Reno Team / Published
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Open the Pool Volume Calculator
A round pool is a cylinder of water. Its volume is the circle area times the water depth, and there are 7.48 gallons in a cubic foot:
gallons = π × (diameter ÷ 2)² × water depth (ft) × 7.48
The one thing people get wrong is the depth: use the water depth, not the wall height. An above-ground pool fills to about 6 inches below the top rail, so a 52-inch wall holds roughly 3.8 ft of water.
Skip the math
Enter the diameter and depth in the pool volume calculator, choose Round, and it returns US gallons, imperial gallons and litres. The chart below is for a quick look-up.
Round pool gallons by diameter and depth
US gallons, rounded to the nearest hundred. Find your diameter down the side and your water depth across the top:
| Diameter | 3.5 ft | 4 ft | 4.5 ft | 5 ft |
|---|---|---|---|---|
| 12 ft | ~2,960 | ~3,380 | ~3,810 | ~4,230 |
| 15 ft | ~4,630 | ~5,290 | ~5,950 | ~6,610 |
| 18 ft | ~6,660 | ~7,610 | ~8,570 | ~9,520 |
| 21 ft | ~9,070 | ~10,360 | ~11,660 | ~12,950 |
| 24 ft | ~11,850 | ~13,540 | ~15,230 | ~16,920 |
| 27 ft | ~14,990 | ~17,130 | ~19,280 | ~21,420 |
| 30 ft | ~18,510 | ~21,150 | ~23,800 | ~26,440 |
Same chart in litres
For metric readers, the same pools to the nearest hundred litres:
| Diameter | 1.1 m | 1.2 m | 1.4 m |
|---|---|---|---|
| 4.5 m | ~17,500 | ~19,100 | ~22,300 |
| 5.5 m | ~26,100 | ~28,500 | ~33,300 |
| 6.4 m | ~35,400 | ~38,600 | ~45,000 |
| 7.3 m | ~46,000 | ~50,200 | ~58,600 |
Worked example
A 24 ft round above-ground pool with a 52-inch wall, filled to about 4 ft:
radius = 24 ÷ 2 = 12 ft
surface area = π × 12² = 452 sq ft
volume = 452 × 4 = 1,810 cu ft
gallons = 1,810 × 7.48 = about 13,540 US gallons
So roughly 13,500 gallons. To work out the volume of a rectangular pool instead, see how many gallons is my pool; to plan the fill, how long does it take to fill a pool.
Frequently asked questions
How many gallons in a 24 foot round pool?
A 24 ft round pool holds about 13,500 US gallons at 4 ft of water, around 11,850 gallons at 3.5 ft, and about 15,200 gallons at 4.5 ft. Most 24 ft above-ground pools with a 52-inch wall fill to roughly 4 ft of water, so 13,500 gallons is the usual working figure. The formula is pi times 12² times the water depth times 7.48.
How do I calculate gallons in a round pool?
Take the radius (half the diameter) in feet, square it, multiply by pi (3.1416), then multiply by the average water depth in feet and by 7.48 gallons per cubic foot. For a 21 ft round pool at 4 ft: 10.5² = 110.25, times pi = 346.4 sq ft, times 4 = 1,385 cu ft, times 7.48 = about 10,360 gallons.
What water depth should I use for an above-ground pool?
Use the actual depth of the water, not the wall height. An above-ground pool is filled to roughly 6 inches below the top rail, so a 52-inch wall holds about 46 inches - close to 3.8 ft - of water, and a 54-inch wall holds about 4 ft. Measure from the floor to the water line for the most accurate figure, then read it off the chart below.
How many gallons in a 15 ft, 18 ft or 30 ft round pool?
At about 4 ft of water, a 15 ft round pool holds roughly 5,300 gallons, an 18 ft about 7,600 gallons, a 21 ft about 10,400 gallons, a 27 ft about 17,100 gallons, and a 30 ft round pool about 21,200 gallons. The chart below gives every common diameter at several water depths.
Does an oval pool use the same formula?
Almost. An oval pool uses pi divided by 4, times the long axis, times the short axis, for the surface area - then times the average depth and 7.48 as before. A 15 by 30 ft oval at 4 ft is about 0.785 × 15 × 30 = 353 sq ft, times 4 times 7.48 = roughly 10,570 gallons. The calculator has an oval setting so you do not have to remember the constant.