Kidney shaped pool volume calculator
A kidney-shaped pool holds about 0.45 × (A + B) × length × average depth × 7.48 gallons, where A and B are the two lobe widths.
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On this page (6 sections)
For example, a 30 ft pool with lobes of 10 and 14 ft and an average depth of 5 ft holds about 12,118 gallons.
Calculator: A, B, length, depths
Measure three distances across the water surface, in feet (or switch to meters):
- Length: the longest straight line from end to end.
- Width A: the widest point across the smaller lobe.
- Width B: the widest point across the larger lobe.
Then enter the water depth at the shallow end and at the deep end. The calculator averages them, which is right for a floor that slopes evenly. The default pool above (30 ft long, lobes of 10 and 14 ft, 3.5 ft shallow and 6 ft deep) comes to about 11,513 gallons with an average depth of 4.75 ft.
If your deep end is a short hopper rather than a steady slope, a plain average overstates the volume. Measure the depth at a few points along the length and average those instead, or weight the average by how much of the length is shallow.
Formula: 0.45 × (A + B) × L × avg depth × 7.48
Gallons = 0.45 × (A + B) × L × average depth × 7.48
7.48 is the number of gallons in a cubic foot. The 0.45 factor is an empirical shape allowance used in pool-industry guides such as Leslie's volume guide. It treats the kidney as a rectangle about 90% as wide as the average of the two lobes, to account for the narrow middle and rounded ends. It's an estimate, not an exact geometric formula, and real kidney pools vary.
How it compares with other shapes of the same size (30 ft long, 5 ft average depth):
| Shape | Formula | Gallons |
|---|---|---|
| Kidney, lobes 10 and 14 ft | 0.45 × 24 × 30 × 5 × 7.48 | 12,118 |
| Rectangle 30 × 12 ft (average width) | 30 × 12 × 5 × 7.48 | 13,465 |
| Ellipse 30 × 12 ft | 0.785 × 30 × 12 × 5 × 7.48 | 10,575 |
Typical kidney sizes, by the same formula:
| Length × lobes | Average depth | Gallons | Liters |
|---|---|---|---|
| 24 ft × 8 / 12 ft | 4.5 ft | 7,271 | 27,524 |
| 30 ft × 10 / 14 ft | 3.5 ft | 8,483 | 32,111 |
| 30 ft × 10 / 14 ft | 4.5 ft | 10,907 | 41,286 |
| 30 ft × 10 / 14 ft | 6 ft | 14,542 | 55,048 |
| 32 ft × 12 / 16 ft | 4.5 ft | 13,573 | 51,378 |
| 36 ft × 14 / 18 ft | 5 ft | 19,390 | 73,397 |
| 40 ft × 16 / 20 ft | 5.5 ft | 26,661 | 100,921 |
Example: 10/14/30 ft, 5 ft ≈ 12,118 gal
- Add the lobe widths: 10 + 14 = 24 ft.
- Multiply by 0.45: 24 × 0.45 = 10.8 ft (the equivalent width).
- Multiply by the length: 10.8 × 30 = 324 sq ft of surface.
- Multiply by average depth: 324 × 5 = 1,620 cubic feet.
- Multiply by 7.48: 1,620 × 7.48 ≈ 12,118 gallons (about 45,870 liters).
A 5% error in volume is a 5% error in every dose. That is smaller than the error of most home test kits.
Freeform pools: calibrate with salt
Many "kidney" pools are really freeform, with a spa bump, a tanning ledge, or uneven lobes. For those, any formula is only an approximation, and how far off it is depends on the shape. The most accurate method needs no tape measure: add a known amount of salt and measure how much the salt level rises.
Volume (liters) = salt added (grams) × 1,000 ÷ rise in ppm
- Test salt with a meter or strip, add a whole bag (for example, 40 lb, which is 18,144 g), brush until it dissolves, circulate for 24 hours, and retest.
- A rise of 400 ppm means about 45,360 liters, or 11,983 gallons.
- Your test's accuracy sets the answer's accuracy: a 10% error in the measured rise is a 10% error in volume. Test before and after with the same meter.
- In a salt water pool, this costs nothing extra if you were topping up anyway. In a chlorine pool, a few hundred ppm of salt is well below the 3,000+ ppm that salt pools run at. Check your equipment manual if you're unsure.
The pool salt calculator shows how much salt a given rise takes. Other shapes: round, oval, and the general pool volume calculator for rectangles and L-shapes. All tools: calculators.
FAQ
How many gallons in a kidney shaped pool?
Most residential kidney pools hold roughly 7,000–27,000 gallons. A common 30 ft kidney with 10 and 14 ft lobes holds about 10,900 gallons at 4.5 ft average depth and about 12,100 gallons at 5 ft. Measure yours and use the calculator for your number.
How to calculate gallons in a kidney shaped pool?
Multiply 0.45 × (width of small lobe + width of large lobe) × length × average depth, all in feet, then multiply by 7.48. Average depth is (shallow + deep) ÷ 2. For metric, use meters and multiply by 1,000 to get liters.
Sources
- Leslie's, Calculating pool volume (kidney-shaped formula): lesliespool.com
- Hayward, How much salt do you add (salt per gallons): hayward.com
- Hayward, AquaRite manual (salt levels): PDF