How many gallons in a kidney-shaped pool?

Kidney and freeform pools have no single width, so the pool trade uses a shortcut: add the widths of the two lobes, multiply by the length and by 0.45. That gives a surface area within a few percent for a classic kidney outline.

How to measure a kidney pool

1. Length (L): the longest straight line from end to end, at the water line.
2. Width A: straight across the bigger, rounder end at its widest.
3. Width B: straight across the smaller end at its widest. Don’t measure across the pinch in the middle.
4. Depths: water surface to floor at the shallowest and the deepest point.

For the example pool, 0.45 × (16 + 12) × 30 = 378 sq ft, and at an average 4.75 ft that is about 13,400 gallons. The 0.45 factor assumes the classic bean shape. If your pool is closer to an oval with a slight waist, the result will be a little low; if it is a lazy L or a lagoon, split it into a rectangle and a circle instead and add the pieces with the project list.

• Gallons per inch: about 236 gallons for 378 sq ft.
• Doses: at roughly 13,400 gallons, label rates “per 10,000 gallons” need multiplying by 1.34.
• Measure the fill if you can. On a freeform pool a hose meter on the next refill beats any formula.

Rectangular pools are simpler — see how many gallons in a 16x32 inground pool. For dosing a pool this size, how much chlorine for a 15,000 gallon pool is the nearest worked example.