Guide
How many gallons is my pool?
Surface area times average depth times 7.48 gives US gallons. The formula for rectangular, round, oval, kidney and L-shaped pools, worked examples, and litres.
Updated · 3 min read
Multiply the water's surface area by its average depth, then by 7.48 to get US gallons (one cubic foot holds 7.48 gallons). A rectangular pool 32 ft by 16 ft, 3.5 ft deep at the shallow end and 5.5 ft at the deep end, averages 4.5 ft deep and holds about 17,200 gallons.
Every chemical dose scales with volume, so this is the number the rest of your pool care rests on. The pool volume calculator does the math for any of the shapes below.
Formulas by shape
Measure in feet, water line to water line, and use the average depth: shallow end plus deep end, divided by two.
| Shape | US gallons |
|---|---|
| Rectangle or square | length × width × average depth × 7.48 |
| Round | diameter × diameter × average depth × 5.9 |
| Oval | length × width × average depth × 5.9 |
| Kidney | 0.45 × (narrow-end width + wide-end width) × length × average depth × 7.48 |
| L-shape | split it into two rectangles and add them |
The 5.9 for round and oval pools is 7.48 × 0.785: a circle or ellipse covers 0.785 (π ÷ 4) of the rectangle drawn around it. The kidney factor, 0.45, is the one pool builders use for that shape.
Worked examples
- Rectangle: 32 × 16 ft, 3.5 to 5.5 ft deep (average 4.5 ft) → 512 ft² × 4.5 ft × 7.48 = about 17,200 gallons.
- Round above-ground: 24 ft across, 4 ft deep → about 13,500 gallons.
- Oval: 30 × 15 ft, 4 ft deep → about 10,600 gallons.
- Kidney: 30 ft long, 10 ft wide at one end and 15 ft at the other, 3.5 to 6 ft deep → about 12,000 gallons.
How to measure your pool, step by step
- Measure the length and width of the water surface. For a round pool, measure the diameter; for a kidney, the width at each end.
- Measure the depth at the shallow and deep ends. A tape on a pole works; measure to the water line, not the top of the wall.
- Average the depths. Add them and divide by two; for a flat floor, use the one depth.
- Multiply using the formula for your shape. Round to a convenient number, such as 17,200 rather than 17,235.
- Write it down. Doses, pump hours and drain amounts all start from it.
Metric
In metres, surface area × average depth gives cubic metres, and each cubic metre is 1,000 litres. A pool 10 m × 5 m, 1.0 to 1.8 m deep (average 1.4 m) holds 70 m³, which is 70,000 litres (about 18,500 US gallons). For round pools, diameter × diameter × average depth × 0.785 gives cubic metres.
Questions people ask
How do I work out gallons in a round pool?
Diameter times diameter, times average depth, times 5.9. A 24-foot round pool 4 feet deep holds about 13,500 gallons.
How do I find the average depth of a sloped floor?
For a floor that slopes evenly from shallow to deep, add the two depths and divide by two. If the deep end is a short, steep hopper, measure the depth at a few points along the pool and average those instead.
Why is my number lower than the builder's figure?
You treat the water that is actually there. Measure to the water line, not the top of the wall or the coping, and your number will usually come out a little lower.
How many litres is a 20,000-gallon pool?
About 75,700 litres. One US gallon is 3.785 litres.