A pool volume calculator that turns your pool shape and a few measurements into the water volume in litres, US gallons and Imperial gallons at once, then estimates how much chlorine to add and what a mains-water fill would cost. It is built for pool owners sizing a chemical dose, anyone draining and refilling, and installers who need a quick, reliable number without reaching for a spreadsheet.
How it works
Every pool volume comes from the same idea: volume equals surface area times average depth. The surface area depends on the shape. A rectangular pool is simply length times width. A round pool uses the circle area, pi times the radius squared, where the radius is half the diameter. An oval pool uses the ellipse area, pi times half the length times half the width. A kidney or freeform pool is irregular, so the tool applies a widely used approximation of about 85 percent of the bounding rectangle, which lands close for most gentle curves.
Depth is handled in two ways. If the floor is flat you enter one depth. If it slopes from a shallow to a deep end, you enter both and the calculator takes the average: the shallow end plus the deep end, divided by two. That average depth is multiplied by the surface area to give the raw volume in cubic metres or cubic feet, which is then converted to litres and gallons using fixed factors (1 cubic metre is 1,000 litres; 1 cubic foot is 7.48 US gallons; 1 US gallon is 3.785 litres; 1 Imperial gallon is 1.201 US gallons). Because the maths is deterministic, the answer is identical every time and nothing leaves your device.
The dosing panel uses standard pool-chemistry rules of thumb. Roughly 5.7 grams of pure available chlorine raises 10,000 US gallons by about 1 ppm, so the tool scales that to your volume and target, then expresses it as grams of 65 percent cal-hypo granules or litres of 12.5 percent liquid chlorine. A shock dose targets about 10 ppm.
Worked example
Take a rectangular pool, 8 m long and 4 m wide, with a sloped floor from a 1.0 m shallow end to a 2.0 m deep end. The surface area is 8 times 4, which is 32 square metres. The average depth is (1.0 plus 2.0) divided by 2, which is 1.5 m. So the volume is 32 times 1.5, which is 48 cubic metres — that is 48,000 litres, about 12,680 US gallons or roughly 10,560 Imperial gallons.
To raise free chlorine by 1 ppm in that pool you need about 11 grams of pure available chlorine, which is roughly 17 grams of cal-hypo granules or about 0.07 litres of liquid chlorine. A full shock to 10 ppm needs ten times that. Filling it from UK mains water at about 3.50 pounds per cubic metre would cost in the region of 168 pounds.
Formula note: volume = surface area × average depth, where average depth = (shallow + deep) / 2 for a sloped floor. Conversions are exact constants, so the only source of error is how closely the shape multiplier matches your real pool.
| Shape | Dimensions | Avg depth | Volume |
|---|---|---|---|
| Rectangular | 8 m x 4 m | 1.5 m | 48,000 L |
| Round | 5 m diameter | 1.4 m | 27,500 L |
| Oval | 9 m x 4.5 m | 1.5 m | 47,700 L |
| Kidney | 8 m x 4 m | 1.5 m | 40,800 L |
Every figure is calculated in your browser — no measurements are uploaded or stored.