Free tool No. 3
How many gallons is my pool?
Multiply the water's surface area by its average depth, then by 7.48 for gallons. A 32 × 16 ft pool, 3.5 to 8 ft deep holds about 22,000 gallons. Pick your shape below for yours.
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Worked example
A 32 × 16 ft pool, 3.5 to 8 ft deep.
- 1
Surface area
32 ft × 16 ft = 512 ft²
- 2
Average depth
(3.5 ft + 8 ft) ÷ 2 = 5.75 ft
- 3
Volume
512 ft² × 5.75 ft = 2,944 ft³
- 4
Gallons
2,944 ft³ × 7.481 gal/ft³ = 22,023 gal
About 22,000 gallons (83,400 litres).
Close enough for dosing: a 5% error in volume moves a chlorine dose by 5%, which is well inside the target range.
Volumes of common pool sizes
| Pool | Gallons | Litres |
|---|---|---|
| 12 × 24 ft rectangle | 12,400 | 46,900 |
| 14 × 28 ft rectangle | 16,900 | 63,800 |
| 16 × 32 ft rectangle | 22,000 | 83,400 |
| 18 × 36 ft rectangle | 27,900 | 105,500 |
| 20 × 40 ft rectangle | 34,400 | 130,300 |
| 15 ft round above-ground | 5,300 | 20,000 |
| 18 ft round above-ground | 7,600 | 28,800 |
| 24 ft round above-ground | 13,500 | 51,200 |
Surface area by shape
| Shape | Surface area |
|---|---|
| Rectangle | length × width |
| Round | 3.14 × (diameter ÷ 2)² |
| Oval | 3.14 × (length ÷ 2) × (width ÷ 2) |
| Kidney | 0.45 × (narrow width + wide width) × length |
| L-shape | split into two rectangles and add them |
Lengths in ft. For a sloped floor, the average depth is (shallow + deep) ÷ 2.
How to measure your pool
- 1
Measure the longest length
Wall to wall at the water line, in feet.
- 2
Measure the width
At the widest point. For a kidney pool, measure both ends: the narrow one and the wide one.
- 3
Measure water depth at both ends
From the water surface to the floor, not the wall height. A weighted string works at the deep end.
- 4
Enter them in the calculator
Pick the shape, then the measurements. The volume updates as you type.
- 5
Save it
Every dose depends on this number, so save it once and let the app use it from then on.
How we calculate
Volume is surface area × average depth. A floor that slopes evenly from shallow to deep averages to the middle of the two; a pool with a steep hopper holds a little less than that.
Conversions use exact factors: 7.48 US gallons per cubic foot (1,728 ÷ 231) and 3.785 litres per gallon, the same factors the chemistry engine uses, so the volume you save and the doses you get agree.
Questions
Why does pool volume matter?
Every dose is proportional to it. Twice the water needs twice the chlorine, acid or salt. A good volume estimate is the single biggest step to accurate doses.
How accurate does it need to be?
Within about 10% is fine for everyday dosing. If you know the real figure from the builder or from how much water it took to fill, use that.
How do I measure a freeform pool?
Pick the closest shape: kidney for curvy pools with two lobes, oval for rounded ones. Or split the pool into simple sections and add their volumes.
How many gallons is a 16 × 32 pool?
Sloping from 3.5 to 8 ft, about 22,000 gallons. The table on this page lists other common sizes.