Calculate the volume of a kidney-shaped pool using the industry-standard two-width formula. Free, instant, in gallons or litres.
Kidney pools are the hardest shape to measure by hand — two lobes and a curved waist make length-and-width guesswork. If your builder’s plan, spec sheet, or survey already lists the pool’s surface area, you don’t need any of that. Switch the calculator to “I know my surface area”, type in the square footage, set your average depth, and read off the gallons. For a kidney pool it’s often the most accurate route.
(Width A + Width B) × Length × 0.45 × Average Depth × 7.48 = US gallons
Measure the full length, the widest bulge (Width A), and the narrowest bulge (Width B). A pool 20 ft long with Width A 10 ft and Width B 8 ft at 8 ft average depth holds (10 + 8) × 20 × 0.45 × 8 × 7.48 ≈ 9,694 gallons. The 0.45 multiplier is the industry standard that accounts for the kidney's curved area — the same constant Inch Calculator and other major tools use.
This calculator uses the precise cubic-foot-to-gallon value (about 7.48 US gallons per cubic foot) for your kidney pool and lets you switch between US gallons, imperial gallons, litres, and cubic metres.
You will need these measurements:
A kidney pool with widths 16 ft and 10 ft, length 30 ft, 5 ft deep: 0.45 × (16 + 10) × 30 × 5 = 1,755 cubic feet, then × 7.48 ≈ 13,128 US gallons.
Approximate capacity at 5 ft average depth, computed with this calculator. Your exact number depends on your real depth.
| Pool size | US gallons |
|---|---|
| 16 × 30 ft kidney | 13,633 |
| 16 × 34 ft kidney | 15,451 |
| 18 × 36 ft kidney | 18,178 |
| 20 × 38 ft kidney | 21,106 |
A kidney pool is defined by two different widths, and getting both is what makes the estimate accurate. Width A is the widest bulge across the larger lobe; Width B is the narrower width across the smaller lobe near the waist. Measure the length down the long axis of the pool. The industry-standard formula — 0.45 × (Width A + Width B) × length — uses the 0.45 factor to account for the curved, pinched kidney outline, which fills less area than a rectangle of the same length and average width. This is the same approximation used by major pool references, so it matches the figures pool professionals work from. As with any in-ground pool, average the shallow and deep depths rather than using a single number.
The method behind this calculator draws on established standards, peer-reviewed academic sources, and reference values:
Results are planning estimates. Where a figure depends on your local rates, codes, or site conditions, confirm with the cited authority or a qualified professional.