Pool Gallon Calculator
Find out exactly how many gallons of water your swimming pool holds. This pool gallon calculator handles rectangle, round, oval, and kidney shapes, plus pools with a sloped bottom (shallow end plus deep end). Knowing gallons is step one for every chemical dose, pump sizing decision, and heater sizing decision you make about your pool.
Pool Gallon Formulas by Shape
- Pool gallon calculator rectangle: Length x Width x Avg Depth x 7.48 gal/ft^3
- Round pool: pi x Radius^2 x Avg Depth x 7.48
- Pool gallon calculator oval: pi x (Length/2) x (Width/2) x Avg Depth x 7.48
- Pool gallon calculator kidney: Length x Width x Avg Depth x 7.0 (irregular bottom coefficient)
For sloped pools, average depth equals (shallow + deep) / 2. This works for most residential in-ground pools where the floor slopes evenly from a shallow end to a deep end.
Typical Pool Sizes in Gallons
- 18 ft round above-ground (52 in deep): about 8,600 gallons
- 24 ft round above-ground (52 in deep): about 14,650 gallons
- 12 x 24 ft oval above-ground: about 8,000 gallons
- 16 x 32 ft rectangular in-ground (5 ft avg): about 19,150 gallons
- 20 x 40 ft rectangular in-ground (3-8 ft slope): about 33,000 gallons
- Kidney 16 x 32 ft at 5 ft avg depth: about 17,900 gallons
Why Pool Gallons Matter
Every chemical dose scales with pool volume. Chlorine, pH adjusters, cyanuric acid, algaecide, and salt all key off gallons. Filter capacity, pump horsepower, and heater BTU output are also sized against gallons. A 10% error in pool volume means a 10% error in every chemical dose and a 10% error on every equipment size. Ten minutes with a tape measure and this calculator is cheaper than a season of cloudy water.
Pool Gallon Calculator Oval Tips
Oval above-ground pools are measured by the overall length (longest point) and the overall width (widest point). The formula uses pi x (Length/2) x (Width/2) for surface area, which is the area of an ellipse. A typical 12 x 24 ft oval at 4 ft average depth is pi x 6 x 12 x 4 x 7.48 = about 6,770 gallons. Most oval liner pools have a flat bottom so single average depth is the right choice.
Pool Gallon Calculator Kidney Shape Notes
Kidney-shaped and freeform pools have curved perimeters and irregular bottoms that make simple length x width math inaccurate. Pool industry practice is to multiply length x width x 0.85 for surface area and use a 7.0 gal/ft^3 coefficient instead of the textbook 7.48, which together account for the curvature and the uneven bottom. Expect results within 5-10% of the real volume. For precision, measure the pool in sections (main body + spa + sun shelf) and add the volumes.