What average depth should I use for pool volume?
For a floor that slopes evenly from one end to the other, use (shallow depth + deep depth) ÷ 2. A pool that is 3 ft at the shallow end and 8 ft at the deep end has an average depth of 5.5 ft, not 8 — using the deep end overstates the volume by a long way.
If the floor is not a single even slope — a flat shallow shelf, then a slope, then a flat deep section — that pool is really three boxes. Work out each section with its own depth and add the three results. The gap between that and a simple two-end average is largest in pools with a long shallow shelf, which is most family pools.
Pool Volume
What this calculator computes
Volume is area times average depth. The calculator works in cubic feet, then converts: gallons = ft³ × 7.48052 and litres = gallons × 3.78541. If you enter metres it multiplies by 3.28084 first.
Average depth is the mean of the shallow and deep ends — (shallow + deep) ÷ 2. That is exact for a floor that slopes evenly from one end to the other, and approximate for a pool with a flat shallow section and a sudden drop.
- Rectangle — length × width
- Circle — π × radius²
- Oval — π × (long ÷ 2) × (short ÷ 2)
- Kidney — treated as a circle on the mean of the two widths, then scaled by 0.8
Worked examples
Computed with the formulas above.
| Size | Avg depth | Volume | Gallons | Litres |
|---|---|---|---|---|
| 20×10ft | 4ft | 800 ft³ | 5,984 gal | 22,653 L |
| 25×12ft | 4.5ft | 1,350 ft³ | 10,099 gal | 38,228 L |
| 30×15ft | 5ft | 2,250 ft³ | 16,831 gal | 63,713 L |
| 40×20ft | 5.5ft | 4,400 ft³ | 32,914 gal | 124,594 L |
Where the number will be off
The kidney shape uses a 0.8 factor because a kidney outline covers roughly four fifths of the circle that encloses it. Real kidney pools vary, so treat that one as an estimate rather than a measurement.
Steps, benches and tanning ledges take volume away; the calculator does not know about them. A pool with a large entry step can hold a few percent less than the number shown. If you are dosing chemicals, round down rather than up.
Frequently asked questions
How are gallons calculated?
Cubic feet × 7.48052. Litres are gallons × 3.78541.
What is average depth?
The mean of the shallow and deep end. That is exact for an evenly sloping floor and approximate otherwise.
Why is the kidney shape multiplied by 0.8?
A kidney outline covers roughly four fifths of the circle that encloses it. It is an estimate, not a measurement.
Do steps and benches change the result?
Yes, they reduce the real volume, and the calculator does not account for them. Round down when dosing chemicals.
Basis and limits
What this calculation assumes
- Volume = surface area × average depth, computed in cubic feet.
- Gallons = ft³ × 7.48052 · Litres = gallons × 3.78541 · Metres are converted with 3.28084.
- Steps, benches and ledges are not subtracted.
- Everything is computed in your browser; nothing is sent to a server.
Where you should not rely on this
Do not use this as the sole basis for chemical dosing. Follow the product label and measure water chemistry directly; over-dosing a pool is harder to undo than under-dosing.
Further reading
Calculate your swimming pool volume in gallons and liters. Supports rectangular, circular, oval, and kidney-shaped pools with variable depths.
Related tools
The formula behind each shape
Every pool volume is an area multiplied by a depth. The only thing that changes between shapes is how the surface area is worked out, and whether the depth is constant:
| Shape | Surface area | Volume |
|---|---|---|
| Rectangular | length × width | length × width × average depth |
| Circular | π × radius² | π × radius² × average depth |
| Oval | (π ÷ 4) × long axis × short axis | that area × average depth |
| Kidney | 0.45 × (width A + width B) × length | that area × average depth |
The kidney figure is a shape factor, not an exact constant: a kidney outline is a curve with no single closed-form area, so the trade is a simple multiplication for an answer that is close enough to dose chemicals with. Expect it to be the least precise of the four.
Average depth, and why it is not the deep end
With a sloping floor the depth to use is the average, not the maximum. For a floor that slopes evenly from shallow to deep, average depth is (shallow + deep) ÷ 2. A pool 3 ft at one end and 8 ft at the other has an average depth of 5.5 ft, not 8.
Pools with a flat shallow section, a slope, and a flat deep section are really three boxes. Calculating each section and adding the results is more accurate than averaging the two extremes, and the difference is largest in pools with a long shallow shelf.
Unit conversions used here
| From | To | Multiply by |
|---|---|---|
| Cubic feet | US gallons | 7.480519 |
| Cubic metres | Litres | 1000 |
| Cubic metres | US gallons | 264.172 |
| US gallons | Imperial gallons | 0.832674 |
| Cubic feet | Litres | 28.3168 |
US and Imperial gallons are not the same unit, and pool chemical labels use whichever is local. A dose calculated in US gallons and applied to an Imperial figure is out by about twenty per cent, which is enough to matter for chlorine.
More answers
Why does my water bill not match the calculated volume?
Filling a pool also fills the pipes, the filter and the balance tank, and some water is lost to evaporation and splash-out during the fill. The calculated figure is the basin only.
Which volume do chemical doses use?
The full basin volume at normal operating level. If the water is low, dose for the actual level rather than the design level — the concentration is what matters.
How much does a cover change the number?
Not at all. A cover reduces evaporation and heat loss, so it changes how often you top up, not how much water the pool holds.