Pool & spa
Pool Volume Calculator
Works out pool volume, which every chemical dose and every piece of equipment sizing depends on.
Result
A cubic foot holds 7.48 US gallons. Average depth works for a floor that slopes evenly; pools with a sharp transition, a spa shelf or a beach entry hold less than this suggests, often by several percent.
Get a Free Business AuditHow the calculation works
Volume in cubic feet times 7.48 gives gallons, because a cubic foot of water holds about 7.48 US gallons. For a rectangular pool that is length times width times average depth. For a round pool it is pi times the radius squared times the average depth. Average depth is the mean of the shallow and deep ends where the floor slopes at a constant rate, which is the usual case, and closer to a weighted average where there is a distinct deep end shelf.
What moves the number
- Average depth, which is where most volume errors come from.
- Shape, since a kidney or freeform pool needs breaking into sections.
- Whether the floor slopes evenly or has a distinct deep end.
- Whether steps, benches and spa spillovers are counted.
Where this one goes wrong
Get this number right once and write it down, because every chemical dose, pump sizing and heater calculation for the life of the pool scales from it. An error here propagates into everything else, and a pool owner working from a volume that is twenty percent wrong is over or under dosing every chemical they add. For freeform shapes, breaking the pool into rectangles and segments and summing them beats estimating a single average, and a few minutes with a tape gives a figure worth having permanently. The 7.48 conversion is the one to remember: cubic feet times 7.48 is gallons.
Before you quote
- Measure average depth rather than assuming it.
- Break irregular shapes into sections and sum them.
- Record the figure somewhere permanent, since everything scales from it.
Where the rules come from
Questions
About this calculator
How do I calculate pool volume?
Length times width times average depth for a rectangle, or pi times radius squared times average depth for a round pool, then multiply cubic feet by 7.48 to get gallons. Average depth is the mean of the shallow and deep ends where the floor slopes evenly.
What about an irregular shaped pool?
Break it into rectangles, triangles and circular segments, work out each one and add them together. That is more accurate than guessing an average width and length for a freeform shape, and since every chemical dose depends on the figure it is worth the extra few minutes.
Why does volume matter so much?
Because every chemical dose, pump sizing and heater calculation scales from it. A volume figure twenty percent wrong means every chemical addition is twenty percent wrong for the life of the pool. It is the one number worth measuring carefully and recording permanently.
The formula
rectangular: length x width x average depth x 7.48; round: pi x r^2 x average depth x 7.48
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How to use this calculator
- Pool shape. Enter your own figure; the page starts at Rectangular.
- Length (ft) (ft). Enter your own figure; the page starts at 32 ft.
- Width (ft) (ft). Enter your own figure; the page starts at 16 ft.
- Diameter if round (ft) (ft). Enter your own figure; the page starts at 21 ft.
- Shallow end depth (ft) (ft). Enter your own figure; the page starts at 3 ft.
- Deep end depth (ft) (ft). Enter your own figure; the page starts at 6 ft.
The result updates as you type, so you can try a figure, see what it does to volume, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| Pool shape | Rectangular |
| Length (ft) | 32 ft |
| Width (ft) | 16 ft |
| Diameter if round (ft) | 21 ft |
| Shallow end depth (ft) | 3 ft |
| Deep end depth (ft) | 6 ft |
What comes out
| Result | Value |
|---|---|
| Volume main result | 17,234 |
| Average depth | 4.5 |
| Volume | 2,304.0 |
| Volume | 65,230 |
| Surface area | 512.0 |
About 17,234 gallons at an average depth of 4.5 feet. Every chemical dose and the pump size both start from this number, so it is worth measuring rather than guessing.
How sensitive the answer is
Holding everything else steady and changing only length (ft), this is what happens to volume. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Length (ft) (ft) | Volume |
|---|---|
| 16 ft | 8,617 |
| 24 ft | 12,925 |
| 32 ft example above | 17,234 |
| 48 ft | 25,851 |
| 64 ft | 34,468 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Pool shape
- Choose from Rectangular, Round, Oval.
- Length (ft) (ft)
- Measured in ft, starting at 32 ft.
- Width (ft) (ft)
- Measured in ft, starting at 16 ft.
- Diameter if round (ft) (ft)
- Measured in ft, starting at 21 ft.
- Shallow end depth (ft) (ft)
- Measured in ft, between 0 and 20, starting at 3 ft.
- Deep end depth (ft) (ft)
- Measured in ft, between 0 and 40, starting at 6 ft.
What the results tell you
| Result | What it is |
|---|---|
| Volume | The headline result. A number. |
| Average depth | A decimal figure. |
| Volume | A decimal figure. |
| Volume | A number. |
| Surface area | A decimal figure. |
Keep going
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