Pool Volume Calculator

This is an estimate, not professional advice. Check your inputs and verify the result against your plans and local building code before you build or order. See terms and disclaimer.

How this calculator works

Choose your pool shape, enter the length, width or diameter, and the shallow and deep-end water depth. The result updates instantly with the volume in gallons and liters, the surface area and an estimated fill time. Each shape uses its own surface-area geometry, shown below, then the same steps: average the two depths, multiply by area for cubic feet, and convert with 7.48 gallons per cubic foot.

Worked example

A 16 ft × 32 ft rectangular pool that slopes from 3 ft in the shallow end to 7 ft in the deep end (5 ft average). Inputs: Length 32 ft, Width 16 ft, Shallow-end depth 3 ft, Deep-end depth 7 ft. Result: 19,150 gal.

Gallons for common pool sizes

Rectangular pools at the average depth shown. Tap a size to load it in the calculator above.

Method & assumptions

Every pool volume comes down to one idea: the surface area of the water times its average depth. The shape only changes how the area is found. A rectangle is length times width. A round pool is pi times the radius squared, where the radius is half the diameter. An oval is pi divided by four times the long axis times the short axis, which is the area of an ellipse. Once you have the area in square feet and the average depth in feet, multiplying them gives the volume in cubic feet.

Most in-ground pools have a sloped floor, so we average the two ends: average depth equals the shallow depth plus the deep depth, divided by two. A pool that runs from 3 feet to 7 feet has a 5 foot average. For a flat-bottom above-ground pool, leave the deep end at zero and the shallow figure is used directly. The single most common mistake is measuring the wall height instead of the water depth, because pools are almost never filled to the very top, so always measure to the actual water line.

To convert cubic feet to US gallons we multiply by 7.48052, the exact figure from NIST, rather than the rounded 7.5 that quick estimates use, and by 28.3168 for liters. Knowing the gallons is not just trivia: every chemical dose, chlorine, shock, muriatic acid and salt, is calculated per gallon, and so is pump and heater sizing, so a volume that is off by a thousand gallons throws off your whole chemistry. For an odd or freeform shape, split the pool into rectangles and half-circles, run each piece here, and add the results. If you also need the deck or coping around the pool, our square footage calculator handles that, and the concrete slab calculator sizes a poured deck.

Pro tips and common mistakes

• Measure the water, not the wall. Pools are rarely filled to the brim. Measure from the floor to the actual water line, not the top of the wall. Even a few inches of difference can swing the gallons by hundreds.
• Average a sloped floor. For a deep-end pool, add the shallow and deep depths and divide by two. The calculator does this when you fill in both ends. A flat above-ground pool just uses the one depth.
• Get the volume right before dosing. Chlorine, shock, acid and salt are all dosed per gallon. An accurate volume is the difference between balanced water and wasting chemicals or chasing cloudy water all season.
• Split freeform pools into pieces. A kidney or L-shaped pool is just a rectangle plus a half-circle. Calculate each basic shape, add the gallons, and you will be within a few percent.
• Plan the fill time. A garden hose runs roughly 9 gallons per minute, so a 19,000 gallon pool takes a day and a half on one hose. Enter your flow rate to see the estimate and consider a water-delivery truck for big pools.

Frequently asked questions

References

• Gallon and cubic foot conversions (NIST Handbook 44)
• Ellipse area (Wikipedia)
• Swimming pool (Wikipedia)

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