Pool Volume Calculator (Gallons)
Find how many gallons your pool holds from its shape and dimensions. Works for rectangular, round, oval and kidney / freeform pools — enter the shallow and deep-end depths and we average them for you.
Calculator
A rectangular pool 32.0 × 16.0 ft at 5.0 ft average depth holds ≈ 19,149 gallons — plan salt and chemicals for ~19,100 gal.
Almost every pool decision starts with one number: how many gallons of water the pool holds. Salt, chlorine, shock, stabilizer, acid and heater sizing are all dosed per gallon, so an accurate volume is the foundation for everything else on this site. This universal calculator handles the four common shapes and turns your tape-measure readings into gallons (and liters) using nothing more than geometry and the fixed conversion of 7.48 US gallons per cubic foot.
Because the deep and shallow ends differ, the volume depends on the average depth, not the maximum depth. Enter both readings and the tool averages them — for a pool with a shallow end of 3 ft and a deep end of 7 ft, the average is 5 ft, and that 5 ft is what drives the gallons.
Formula
Volume in cubic feet is the pool footprint times the average water depth; multiply by 7.48 to get US gallons. The footprint depends on the shape:
- Rectangular: gal = length × width × avg depth × 7.48
- Round: gal = π × (diameter ÷ 2)² × avg depth × 7.48
- Oval: gal = π × (length ÷ 2) × (width ÷ 2) × avg depth × 7.48
- Kidney / freeform: gal ≈ 0.45 × (width A + width B) × length × avg depth × 7.48 (estimate)
where avg depth = (shallow depth + deep depth) ÷ 2. The round and oval formulas are the rectangular one scaled by π/4 ≈ 0.785, which is why a round or oval pool holds roughly 21% less water than a rectangle of the same overall length and width.
Worked example
Take a rectangular pool 32 ft long by 16 ft wide, with a 3 ft shallow end and a 7 ft deep end.
- Average depth = (3 + 7) ÷ 2 = 5 ft.
- Footprint = 32 × 16 = 512 ft².
- Volume = 512 × 5 = 2,560 ft³.
- Gallons = 2,560 × 7.48 = 19,149 gallons.
Round that to ~19,000 gallons when you dose chemicals. A round 24 ft pool at a 4 ft average depth, by contrast, holds π × 12² × 4 × 7.48 ≈ 13,536 gallons — the same footprint idea, scaled by the circle.
Measuring your pool accurately
The math is exact; the weak link is your measurements. A few field tips keep the estimate honest:
- Measure the water, not the coping. Use the actual waterline length and width, and the real water depth, not the wall height.
- Average depth is the whole game. For a pool that slopes gradually, averaging the shallow and deep ends is accurate. For an "L" or a pronounced hopper bottom, measure the depth in several spots and average those readings before entering them.
- Above-ground pools are usually round or oval with a uniform depth — put the same number in the shallow and deep fields, and subtract a few inches because they are rarely filled to the very top.
- Freeform and kidney pools are always an estimate. The 0.45 factor is a reliable rule of thumb, but round up a little when buying salt or chemicals so you are never short.
Once you know the gallons, the same figure feeds every other tool here: the salt calculator, the chlorine dose, the heater sizing and the fill cost. Bookmark your number so you only measure once.
Reference table
Full-size, rectangular in-ground pools, gallons at three average depths (gal = length × width × avg depth × 7.48):
| Size (ft) | 4.0 ft avg | 4.5 ft avg | 5.0 ft avg |
|---|---|---|---|
| 12 × 24 | 8,617 | 9,694 | 10,771 |
| 16 × 32 | 15,319 | 17,234 | 19,149 |
| 18 × 36 | 19,388 | 21,812 | 24,235 |
| 20 × 40 | 23,936 | 26,928 | 29,920 |
| 16 × 40 | 19,149 | 21,542 | 23,936 |
Round and oval pools hold about 21% less than a rectangle of the same length × width (the π/4 ≈ 0.785 factor). See the full gallons chart and the shape multipliers.