Boneyard Tools

How to Calculate Swimming Pool Volume in Gallons

Measure a rectangular, round or oval pool, find the average depth, and convert cubic feet to US gallons and liters with worked examples.

Open the Pool Volume Calculator →

Surface area depends on the shape

Every volume starts with the water surface area. A rectangular pool is simply length times width, so a 32 by 16 ft pool covers 512 square feet. A round pool uses pi times the radius squared, which for an 18 ft diameter (9 ft radius) is about 254.5 square feet. An oval is treated as an ellipse, pi times half the length times half the width, so a 30 by 15 ft oval covers about 353.4 square feet, noticeably less than the 450 square feet a rectangle of the same footprint would have. Getting the shape right matters more than any rounding later.

Average depth handles a sloped floor

Most in-ground pools slope from a shallow end to a deep end. The average depth is the shallow depth plus the deep depth divided by two, so a 3 ft to 7 ft slope averages 5 ft. Multiply the surface area by this average to get cubic feet: 512 square feet times 5 ft is 2,560 cubic feet. For a flat-bottom pool, leave the deep depth blank and the single depth is used directly. This mean-depth method is exact for a straight slope and a close estimate when there is a hopper, bench or shallow ledge.

Convert cubic feet to gallons and liters

Water volume in cubic feet becomes US gallons when you multiply by 7.480519, the number of gallons in a cubic foot. So 2,560 cubic feet is about 19,150 gallons. To reach liters, multiply gallons by 3.785412, giving roughly 72,491 liters for the same pool. The calculator carries full precision internally and only rounds the display, so the gallon and liter figures always agree with the cubic-foot value you see.

Why an accurate volume matters

Almost every pool decision scales with gallons. Chlorine, muriatic acid, cyanuric acid, salt and algaecide are all dosed per volume, so a volume that is off by 20 percent pushes every chemical off by the same amount. Turnover, the time your pump needs to cycle the whole pool, also depends on gallons divided by flow rate. Measure once carefully, save the number, and reuse it across the pool chlorine, salt and heater calculators rather than re-guessing each season.

Frequently asked questions

Should I measure to the top of the wall or the waterline?

Measure depth to the normal waterline, not the top of the coping. The freeboard above the water is not part of the volume you treat or heat, so including it would overstate every chemical dose.

Why does an oval hold less than a rectangle?

An oval is an ellipse, and an ellipse covers about 78.5 percent of the rectangle that would just enclose it. That is the pi over 4 factor, so a 30 by 15 ft oval holds far less water than a 30 by 15 ft rectangle.

How do I estimate a kidney or freeform pool?

Break it into simpler shapes, calculate each with this tool, and add the volumes. Alternatively, approximate the whole pool as an oval using its longest length and widest width, which slightly overstates the total.