How many gallons is my pool?
Work out the surface area, multiply by the average water depth to get cubic feet, then multiply by 7.48, the number of gallons in a cubic foot. Measure water depth, not wall height: the water usually sits halfway up the skimmer.
Gallons = surface area (sq ft) × average depth (ft) × 7.48
Average depth = (shallow end + deep end) ÷ 2
A 32 × 16 ft rectangular pool, 3.5 ft at the shallow end and 8 ft at the deep end: 512 sq ft × 5.75 ft = 2,944 cu ft × 7.48 = 22,021 gallons, or 83,359 litres.
Pool volume formulas by shape
| Shape | Surface area | Gallons |
|---|---|---|
| Rectangle | Length × width | L × W × avg depth × 7.48 |
| Round | 0.785 × diameter² | D × D × avg depth × 5.9 |
| Oval | 0.785 × length × width | L × W × avg depth × 5.9 |
| Kidney | 0.45 × (A + B) × length | 0.45 × (A + B) × L × avg depth × 7.48 |
The 5.9 factor is π ÷ 4 × 7.48, rounded. The calculator uses the unrounded value. For a kidney pool, A and B are the widths across the two rounded ends, measured at their widest points. The 0.45 factor is the standard pool-industry approximation for a kidney shape, so treat the result as an estimate.
Round pool volume calculator
Round pools, including most above ground pools, have a flat bottom, so the shallow and deep depths are the same. A 24 ft round pool with 4.5 ft of water holds about 15,227 gallons.
| Round pool diameter | Gallons at 4 ft of water |
|---|---|
| 12 ft | 3,384 |
| 15 ft | 5,287 |
| 18 ft | 7,614 |
| 21 ft | 10,363 |
| 24 ft | 13,535 |
| 27 ft | 17,131 |
| 30 ft | 21,149 |
Kidney pool volume calculator
Measure the overall length, then the width across each rounded end. A kidney pool 30 ft long, 16 ft and 12 ft across the ends, 3.5 ft to 6.5 ft deep: 0.45 × 28 × 30 = 378 sq ft × 5 ft = 1,890 cu ft, or about 14,137 gallons.
Oval pools
An oval pool is treated as an ellipse. A 30 × 15 ft oval above ground pool with 4 ft of water holds about 10,575 gallons. Pools with straight sides and rounded ends are a little bigger than a true ellipse, so this slightly underestimates them.
Pool volume in litres
One US gallon is 3.785 litres, and 1,000 litres is one cubic metre. The calculator shows litres alongside gallons. If you measure in metres, multiply surface area in square metres by average depth in metres to get cubic metres, then by 1,000 for litres.
Why the number matters
Every chemical dose is based on volume, so an error here carries into everything you add. Pools with a steep hopper or a large flat deep end hold more or less than a simple average suggests. For those, split the pool into sections, work out each one, and add them up. Once you have the number, use the pool chemical calculator to dose.
Questions
How do I calculate how many gallons are in my pool?
Multiply surface area in square feet by average water depth in feet, then by 7.48. For a round pool, use diameter × diameter × average depth × 5.9.
How many gallons is a 24 ft round pool?
About 13,500 gallons at 4 ft of water and about 15,200 gallons at 4.5 ft.
How do I find the average depth of a pool?
Add the water depth at the shallow end to the water depth at the deep end and divide by 2. Measure the water, not the wall.
How many litres are in a gallon?
One US gallon is 3.785 litres. Multiply gallons by 3.785 to get litres.