Pool Volume Formulas (With Examples)
The exact formulas this calculator uses for rectangular, circular, oval and irregular swimming pools, with worked examples.
· 9 min read
Every result on this site starts as cubic metres. Linear measurements are converted to metres first, the shape formula is applied, then the volume is expressed in litres, US gallons and imperial gallons. The formulas below are the ones the calculator uses — there is no hidden “fudge factor”.
Convert to metres
- 1 foot = 0.3048 m
- 1 inch = 0.0254 m
- 1 centimetre = 0.01 m
Do the conversion before multiplying. Mixing feet of length with metres of depth is the most common error in hand calculations.
Rectangular pools
Example: 8 m × 4 m × 1.5 m = 48 m³ = 48,000 litres. That is the default worked example on the homepage.
Circular pools
Example: a 6 m diameter pool that is 1.2 m deep. Radius = 3 m. Volume = π × 9 × 1.2 ≈ 33.93 m³ ≈ 33,930 litres.
Oval (elliptical) pools
a = length ÷ 2, b = width ÷ 2
An oval is treated as an ellipse, not as a rectangle with rounded corners. Example: length 10 m, width 5 m, depth 1.4 m. Semi-axes a = 5 m and b = 2.5 m. Volume = π × 5 × 2.5 × 1.4 ≈ 54.98 m³ ≈ 54,980 litres.
Irregular pools
Sketch the outline, split it into the shapes above, calculate each section, and add them. Kidney pools are usually two ovals; an L-shape is two rectangles. See pool shapes for how those outlines map onto the calculator.
Litres and gallons
- 1 m³ = 1,000 litres (exact)
- 1 US gallon = 3.785411784 litres
- 1 imperial gallon = 4.54609 litres
The 48 m³ example is therefore 48,000 litres, about 12,680 US gallons and 10,559 imperial gallons. A longer walkthrough is in the conversion guide.
Sloped floors
Substitute average depth = (shallow + deep) ÷ 2. That is an approximation of a constant slope; it is the method used by most dosing charts and is accurate enough for chemicals, filling and heating. Hopper floors with a steep centre pit should use extra depth readings.
Measure first with the measurement guide, then run the calculator.