How to use the pool volume calculator
Knowing how much water a pool holds is the starting point for almost every other decision about it: the filter and pump size, the heater, the chemical doses, the cost and time to fill it, and the structural load on a roof terrace or podium. This calculator handles the common pool shapes and sloped floors in US or metric units.
- Pick the shape. For round pools, enter the diameter as the length. For kidney pools, enter the overall length and the widest point of each lobe.
- Enter the water depth at the shallow and deep ends. For a flat floor, enter the same value twice.
- Enter your fill flow rate to see how long filling will take. Time how long your hose takes to fill a bucket if you are not sure.
- Set a turnover time to see the pump flow needed to filter the whole volume in that time.
Pool volume formulas
Average depth = (shallow + deep) ÷ 2
Rectangle: V = L × W × avg depth
Round: V = π × (D ÷ 2)² × avg depth
Oval: V = π × (L ÷ 2) × (W ÷ 2) × avg depth
Kidney (estimate): V = 0.45 × (A + B) × L × avg depth
US gal = ft³ × 7.48 · litres = m³ × 1,000
Pump flow = volume ÷ (turnover hours × 60)
Using the average depth is exact for a floor that slopes evenly from end to end. Pools with a steep hopper under the diving area hold a little less than the simple average suggests, so split those into sections if you need a precise figure.
| Pool | Approximate volume |
|---|---|
| 12 × 24 ft rectangle, 4 ft flat | 8,600 gal (32.6 m³) |
| 16 × 32 ft rectangle, 3.5–8 ft | 22,000 gal (83 m³) |
| 24 ft round, 4 ft water | 13,500 gal (51 m³) |
| 8 × 4 m rectangle, 1.2–1.8 m | 48,000 L (12,700 gal) |
| 2.0 m round hot tub, 0.9 m water | 2,830 L (750 gal) |
Worked examples
A sloped rectangular pool
A 32 × 16 ft pool runs from 3.5 ft to 8 ft of water, so the average depth is 5.75 ft. The volume is 32 × 16 × 5.75 = 2,944 ft³, or about 22,000 US gallons. At 8 gpm from a hose, filling takes about 46 hours, and an 8-hour turnover needs a pump moving about 46 gpm through the filter.
An above-ground round pool
A 24 ft round pool with 4 ft of water: π × 12² × 4 = 1,810 ft³, or about 13,500 gallons. That is about 51 tonnes of water, which is why the ground under it must be level and firm.
A metric pool
An 8 × 4 m pool from 1.2 m to 1.8 m deep has an average depth of 1.5 m, so it holds 8 × 4 × 1.5 = 48 m³, or 48,000 litres. At 30 L/min, filling takes about 27 hours.
Who this calculator helps
- Architects and landscape architects sizing pools, plunge pools and water features and checking water loads on roof decks and podiums.
- Pool builders and service companies quoting fills, pumps, filters and heaters.
- Homeowners working out chemical doses, fill costs and how long a refill will take.
- Hotel and facility managers keeping records of pool volumes for water treatment.
Practical tips
- Water weighs about 62.4 lb per ft³ (1,000 kg per m³). A rooftop pool's load needs a structural engineer, not just a volume.
- Plan the deck around the pool with the paver calculator or the deck calculator, and work out excavation with the excavation calculator.
- If you plan to top up the pool from the roof, the rainwater harvesting calculator estimates how much water the roof can collect in a year.
- Check the local rules on fencing, gates and drain covers early; they shape the layout as much as the pool itself.
Want to see a pool in your garden before you dig? Try a design on a photo of the yard with AI Landscape Design.
