Pool Volume Calculator
Pick your shape, enter the dimensions, get your gallons. If your floor slopes, use the sectioned option rather than a single average depth, because a single average overstates most pools.
Is that right?
Enter your measurements in feet.
Your pool holds about
gallons
cubic feet
If your pool has a flat shallow end and a hopper, the sectioned option will be more accurate. This estimate may be high.
Check your units, these should be feet.
Show the working
Why this is worth doing carefully
Every chemical dose you will ever calculate has your volume in it. An error here is a permanent multiplier on everything else, and it is the reason behind most of the “I added six bags and nothing moved” stories on the pool forums.
Owners know it is the weak link. There is a thread on Trouble Free Pool where someone asks whether they can derive their pool volume by adding one bag of salt, because no tool does it for them. We wrote that method up, and it is below.
The formulas this uses
Dimensions in feet, result in US gallons. A cubic foot holds 7.48 gallons.
| Shape | Formula |
|---|---|
| Rectangle or square | length × width × average depth × 7.5 |
| Circle | diameter × diameter × average depth × 5.9 |
| Oval | length × width × average depth × 5.9 |
| Freeform | split into rectangles and part-circles, add the results |
Circles and ovals share a multiplier because the area of an ellipse is π/4 × length × width. If a guide tells you to use 6.7 for an oval, it is repeating an old error that will overstate your volume by about 14%.
The average depth trap
If your floor slopes evenly end to end, average depth is just shallow plus deep over two.
Most pools are not built that way. The common build is a flat shallow section, a slope, then a deep end or hopper, and the deep section usually covers less floor area than the shallow one. Taking a straight average of the two depths therefore overstates your volume.
Worked example, a 16 × 32 pool with 18 feet of 3.5 foot shallow, 8 feet of slope, 6 feet of 7 foot deep:
| Section | Calculation | Cubic feet |
|---|---|---|
| Shallow | 16 × 18 × 3.5 | 1,008 |
| Slope | 16 × 8 × 5.25 | 672 |
| Deep | 16 × 6 × 7 | 672 |
| 2,352 × 7.48 | 17,593 gallons |
The naive version, 16 × 32 × 5.25 × 7.48, gives 20,106 gallons. That is 14% high, and every dose calculated from it would be 14% high too.
Check it once against your water meter
Worth doing the first time. Read your meter, fill or top up a measured amount, read it again. Most US residential meters read in cubic feet, so multiply by 7.48. If this disagrees with your calculation by more than roughly 10%, trust the meter and go back over your measurements.
The salt trace method, for an exact figure
This is the only method that measures the water instead of the hole, and it is more accurate than any formula if you run it carefully.
Add a precisely known weight of salt, let it dissolve and distribute, then measure the rise in salinity:
volume in gallons = (pounds added × 120,000) ÷ ppm rise
Add 40 lbs, see a 400 ppm rise, and you have 12,000 gallons. See a 270 ppm rise and you have closer to 17,800.
Conditions that make it work: test before and after with the same method on the same day, wait 24 to 48 hours with the pump running and the floor brushed, do not run it in the rain, and do not do it if you are already near your target salinity. The step-by-step version with a worksheet and error margins is in the free True Pool Volume Workbook.
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Got your gallons? Take them to the pool salt calculator.