Pool Volume Calculator
Every pool chemical dose, heater size and pump runtime starts with one number: how much water the pool holds. This pool volume calculator handles rectangular and round pools with sloped floors.
Measure length, width (or diameter) and the depth at both ends — the calculator averages the slope for you.
Enter valid values to see the results.
Formula
Average depth = (shallow + deep) ÷ 2. Metric volume in m³ × 1,000 = litres. Imperial volume in ft³ × 7.48 = US gallons.
How to measure
- Measure the water surface length and width, not the coping edge.
- Measure depth at the shallowest and deepest points with a pole marked in centimetres or feet.
- For constant-depth pools, enter the same value for both depths.
Worked example
Practical tips
- Round the volume up when dosing chemicals — underdosing chlorine is the main cause of cloudy water.
- Measure again after the first fill: builder drawings often differ from the finished shell by 5–10%.
- A pool loses 3–7 mm of water per day to evaporation in summer — top up before chemical dosing.
- For kidney or freeform pools, split the surface into rectangles and circles and add the volumes.
Waste allowance
No waste allowance applies — but round the final volume up to the nearest 1,000 litres (or 500 gallons) for chemical dosing.
Common pool sizes and volumes
| Pool size | Avg depth | Volume |
|---|---|---|
| 6 × 3 m (20 × 10 ft) | 1.4 m | 25 m³ / 25,000 L |
| 8 × 4 m (26 × 13 ft) | 1.5 m | 48 m³ / 48,000 L |
| 10 × 5 m (33 × 16 ft) | 1.6 m | 80 m³ / 80,000 L |
| Round Ø 4.5 m (15 ft) | 1.2 m | 19 m³ / 19,000 L |
Common mistakes
- 1 Using the maximum depth instead of the average — this overstates volume by 15–25% on sloped pools.
- 2 Measuring to the top of the wall instead of the actual water line.
- 3 Confusing US and imperial gallons: 1 US gallon = 3.785 L, 1 imperial gallon = 4.546 L. This calculator uses US gallons.
- 4 Dosing chemicals by guesswork instead of measured volume — algae treatment then costs more than the measurement.
Frequently asked questions
How many litres are in an 8 × 4 m pool?
At an average depth of 1.5 m: 8 × 4 × 1.5 = 48 m³ = 48,000 litres (about 12,700 US gallons).
How do I calculate volume for a sloped pool?
Average the depths: (shallow + deep) ÷ 2, then multiply by surface area. This is accurate for straight slopes.
How many gallons is my round pool?
Diameter squared × average depth × 5.9 = US gallons (for feet). A 15 ft round pool at 4 ft deep: 15² × 4 × 5.9 ≈ 5,310 gallons.
Why does pool volume matter?
Chlorine, algaecide, pH adjusters, heater power and pump run time are all specified per 1,000 litres or gallons — wrong volume means wrong dosing.
How long does it take to fill a pool?
A garden hose delivers 1,000–2,000 L/h (300–500 gal/h). A 48,000 L pool takes 24–48 hours. Check the water meter or well capacity first.