Swimming Pool Volume Calculator
Works out how much water a pool holds, in litres, cubic metres and both kinds of gallon, plus how long it takes to fill and what the water costs. The volume is what every chemical dose is based on.
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The formula
volume = surface area × (shallow depth + deep depth) ÷ 2 round: π⁄4 × D²; oval: π⁄4 × L × W; kidney ≈ 0.75 × L × W 1 m³ = 1,000 L = 264.2 US gal = 220 imperial gal
Averaging the two depths is exact for an evenly sloping floor and close enough for most pools. The kidney factor of 0.75 is the pool industry’s standard approximation for a freeform outline inside its bounding rectangle.
What to watch out for
Why the volume matters beyond filling it:
- Every dose is per volume. Chlorine, pH adjusters and algaecide are all calculated on the litres in the pool. A 20% error in volume is a 20% error in every dose, for the life of the pool.
- Pump and filter sizing is done on turnover — the whole volume through the filter in a set number of hours, typically four to six.
- Heating cost scales with volume directly.
If the shape is irregular, measure it as sections — a rectangle plus a half-circle, say — and add them, rather than forcing it into one formula.
Frequently Asked Questions
How many litres in an 8 × 4 m pool?
With a 1 m shallow end and 1.8 m deep end, the average depth is 1.4 m, so 8 × 4 × 1.4 = 44.8 m³, which is 44,800 litres or about 11,800 US gallons.
How long does it take to fill a pool from a hose?
A garden tap gives 10–20 L/min. At 15 L/min, 44,800 litres takes about 50 hours — over two days of continuous running, which is why larger pools are filled by tanker.
How do I calculate the volume of a kidney-shaped pool?
Multiply the longest length by the widest width, then by 0.75 for the freeform shape, then by the average depth. It is an approximation; measure the pool as two or three simple shapes if you need better.