Pool Volume Calculator (Round / Oval)
Find gallons in a round or oval swimming pool from diameter or major and minor axes.
Includes constant-slope sloped-bottom adjustment.
Round pool formula. Volume = π × radius² × average depth × 7.48. Radius is half the diameter. Most above-ground pools are round and most are flat-bottomed, so average depth equals actual depth.
Oval pool formula. Volume = π × (a × b) × average depth × 7.48, where a is half the long axis and b is half the short axis. An oval is essentially an ellipse.
The depth question for above-ground pools. Manufacturers list a wall height (e.g. 52 inches) but you almost never fill water all the way to the top. Subtract 6 inches for the actual water depth. A 52-inch wall holds about 46 inches of water = 3.83 feet.
Why pi shows up here and not in the rectangular calculator. The base shape of the pool (the footprint) determines which area formula you need. Rectangle = length × width, no pi. Circle = π × r². Ellipse = π × a × b. The depth multiplication is the same for all.
Worked example — 24 ft round above-ground pool, 4 ft of water:
- Radius = 12 ft
- Cubic feet = π × 12² × 4 = 1,810
- Gallons = 1,810 × 7.48 = 13,540
That puts it at the small end of “average backyard pool.” Most 24-footers actually hold 12,000 to 14,000 gallons depending on water height.
Sloped bottom on a round pool. Some inground round pools have a deep center. Use average depth: (shallow + deep) / 2. A round pool that goes from 3 ft at the wall to 6 ft in the center averages 4.5 ft.
Common mistake. People sometimes plug in diameter when the formula wants radius. The output ends up four times too large. If your number looks suspicious, divide by 4 — you probably forgot to halve the diameter.