Round Pool Volume Calculator (Gallons)
Enter the diameter and the water depth to find how many gallons a round or above-ground pool holds. Ideal for the classic 15, 18, 24 and 27 ft above-ground models.
Calculator
A round pool Ø 24.0 ft at 4.5 ft average depth holds ≈ 15,227 gallons.
Round pools — especially above-ground models — are the most common backyard pool in the US, and their volume is delightfully simple: it depends only on the diameter and the water depth. Because most above-ground pools have a single uniform depth, you often enter the same number in both depth fields; if you have a soft-sided or hopper-bottom pool with a shallow and deep area, enter both and the tool averages them.
Getting the gallons right is what lets you dose salt and chlorine correctly and size a heater or pump for an above-ground setup, where over-dosing is easy because the water volume is smaller than an in-ground pool.
Formula
A round pool is a cylinder of water, so:
gallons = π × (diameter ÷ 2)² × avg depth × 7.48
with avg depth = (shallow + deep) ÷ 2 and 7.48 US gallons per cubic foot. The (diameter ÷ 2)² term is the radius squared; π turns it into the area of the circle. Doubling the diameter quadruples the gallons, which is why a 24 ft pool holds far more than two 12 ft pools.
Worked example
A 24 ft round pool filled to a 4.5 ft depth:
- Radius = 24 ÷ 2 = 12 ft; radius² = 144 ft².
- Surface area = π × 144 ≈ 452 ft².
- Volume = 452 × 4.5 ≈ 2,036 ft³.
- Gallons = 2,036 × 7.48 ≈ 15,228 gallons.
The same pool at only 4 ft of water holds π × 12² × 4 × 7.48 ≈ 13,536 gallons — a reminder that even a few inches of fill level noticeably change the volume.
Above-ground pool tips
Above-ground pools rarely hold as much as their nominal size suggests, for two reasons:
- They are not filled to the rim. Most are filled to the bottom of the skimmer, a few inches below the top rail. Measure the actual water depth, not the wall height.
- The listed size is the frame, not the water. A "24 ft" pool measures 24 ft across the outside of the frame; the water circle is a little smaller. For dosing purposes the difference is minor, but it is one more reason to round chemical doses down slightly and re-test.
Once you have the gallons, move on to the salt calculator or the chlorine dose. If your pool is oval rather than round, use the oval calculator instead.