Pool Volume Calculator
Size backyard pool fill water in gallons from length, width or diameter, and shallow-to-deep depth. Compare ×7.5 department gallons with the exact 1728/231 conversion.
Formula example
A 16 ft by 32 ft pool averaging 4.75 ft deep holds 2,432.00 ft³. At 7.5 gal/ft³ that is 18,240 department gallons; at 1728/231 gal/ft³ the exact fill is 18,193 gallons.
FAQ
Why are there two gallon numbers?
Many pool charts use 7.5 gallons per cubic foot. The US gallon is exactly 231 cubic inches, or 1728/231 gallons per cubic foot—about 7.48052. The gap on a 16×32 ft pool with 3.5–6 ft depth is 18,240 versus 18,193, not a rounding mistake.
How is kidney pool area estimated?
This tool uses (width A + width B) × length × 0.45, a common kidney outline shortcut. O8 on a 32 ft long pool with 16 ft and 10 ft widths shows 374.4 ft² surface before depth.
What if my pool has a hopper or ledge?
The slope is assumed straight from shallow to deep. Split unusual bottoms into sections, run each, and add the gallons.
How do I size salt after this?
Use the salt calculator link with your department gallons. The default rectangle here passes 18,240 gallons forward for salt dosing on a fresh fill.
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By Home Yard Calc Editorial Team · Sources listed on the methodology page · Last updated October 26, 2026
Estimates only. Densities, coverage and salt targets vary by product, moisture and manufacturer. Confirm with your supplier or equipment manual. Not a substitute for professional design, soil engineering or pool service.