Kidney and freeform pools aren't rectangles — measure a couple of widths, and get gallons with the right shape factor.
The longest straight-line measurement.
Your pool holds about
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In liters
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Average width used
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Average depth used
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A close estimate — freeform shapes vary, so treat it as accurate to within a few percent, which is plenty for dosing. Round to the nearest thousand gallons for chemical math.
A kidney pool is a rectangle with the corners curved in and one side pinched — so you can't use a single width. Averaging the widest and narrowest measurements captures the taper, and the 7.0 factor (versus 7.5 for a true rectangle) accounts for the water the curves remove. It's an estimate, but a good one — within a few percent of a professionally measured fill.
A worked example
A kidney pool 30 ft long, 16 ft at its widest and 10 ft at its narrowest, sloping from 3 ft to 6 ft deep: average width 13 ft, average depth 4.5 ft, so 30 × 13 × 4.5 × 7.0 ≈ 12,285 gallons — round to 12,000 for dosing. That's the number every chemical calculator on this site needs.
Now put the number to work
Save your gallons and feed it into the chlorine,stabilizer, and salt calculators — they all dose by volume. If your pool is a simple rectangle, round, or oval instead, the standard pool volume calculator has those shapes, and above-ground owners have a dedicated calculator too.
Frequently asked questions
How do you calculate the volume of a kidney-shaped pool?
The trick that works surprisingly well: measure the length, then measure the width at the widest point AND the narrowest point and average them. Multiply length × average width × average depth × 7.0 (a shape factor for kidney/freeform pools) for gallons. This calculator does that math — the 7.0 factor accounts for the curved, tapered outline of a kidney vs a straight rectangle.
What's the multiplier for a freeform or kidney pool?
Rectangles use 7.5 gallons per cubic foot of a boxy shape; kidney and freeform pools use about 7.0 because the curves and taper remove some water compared to a rectangle of the same length and width. It's an estimate — freeform shapes vary — but it lands within a few percent, which is close enough for chemical dosing.
How do I measure the depth of a kidney pool?
Average depth, not the deepest point. For a pool that slopes from shallow to deep, average depth ≈ (shallow depth + deep depth) ÷ 2. If it has a flat shallow section, a slope, and a flat deep end, measure each and weight them — but the simple average is fine for dosing purposes on most backyard pools.
Why do I need to know my kidney pool's volume?
Every chemical dose depends on it — chlorine, acid, stabilizer, salt, algaecide are all measured per gallon. Guess your volume wrong on a freeform pool (easy to do, since it's not a simple rectangle) and every dose all season is off. Measure once, write it down, and every other calculation gets accurate.