Pool Volume Calculator
Work out how many gallons of water your pool holds, based on its shape, dimensions and average depth — useful for chemical dosing, fill time estimates, or heater sizing.
How this calculator works
Each shape uses a standard volume formula, converted to gallons using the fixed 7.48 gallons-per-cubic-foot constant:
rectangular: gallons = length × width × avg depth × 7.48 circular: gallons = π × radius² × avg depth × 7.48 oval: gallons = π × (length ÷ 2) × (width ÷ 2) × avg depth × 7.48 avg depth = (shallow depth + deep depth) ÷ 2
Worked example
A rectangular pool, 32 ft × 16 ft, 3 ft shallow end, 8 ft deep end:
- Average depth: (3 + 8) ÷ 2 = 5.5 ft.
- Surface area: 32 × 16 = 512 sq ft.
- Volume: 512 × 5.5 = 2,816 cu ft.
- Gallons: 2,816 × 7.48 ≈ 21,064 gallons.
Getting an accurate shape estimate
The circular and oval formulas assume a true circle or ellipse. Most in-ground circular pools are close enough to this shape for an accurate result. A freeform or kidney-shaped pool is harder to estimate with one formula — splitting it mentally into two or three simpler shapes (a rectangle plus a half-circle, for example), calculating each separately, and adding the totals gives a more accurate number than forcing an irregular shape into a single oval estimate.
What pool volume is used for
| Use | Why volume matters |
|---|---|
| Chemical dosing | Chlorine and other chemicals are dosed per gallon — see the pool chemical calculator |
| Heater sizing | Larger volumes take longer to heat for a given heater output |
| Fill time | Divide gallons by your hose or fill line's flow rate |
| Water bill estimate | Most utilities bill water by volume, often in gallons or cubic feet |
Frequently asked questions
How do I measure average pool depth correctly?
Measure the shallowest point and the deepest point separately, then average the two — (shallow + deep) ÷ 2. This works well for a pool with a fairly even, gradual slope. A pool with a distinct flat shallow section and separate deep well can be estimated more accurately by treating it as two volumes and adding them.
Where does the 7.48 gallons-per-cubic-foot constant come from?
One cubic foot of water holds almost exactly 7.48 US gallons — a fixed physical conversion, not an estimate. Every volume this calculator produces in cubic feet is multiplied by 7.48 to convert to gallons.
How accurate is an oval or kidney-shaped pool estimate?
The oval formula treats the pool as a true ellipse, a close approximation for a symmetric oval but less accurate for an irregular kidney or freeform shape. For a very irregular shape, splitting the pool into two or three simpler sections and adding their volumes gives a more accurate total.
Why does pool volume matter for chemical dosing?
Chlorine and other pool chemicals are dosed based on total volume, since the same amount of chemical produces a much higher concentration in a smaller pool than a larger one. An accurate gallon figure here is the starting point for correct dosing.