Pool Volume Calculator: How Many Gallons Is Your Pool?

Pool volume calculator: pick a shape, enter feet, get gallons

Enter the length, width and the depth at both ends. For a round pool the width box becomes the diameter; for a kidney pool add the width of the second lobe.

The calculator averages your shallow and deep readings, multiplies the surface area by that average depth and converts cubic feet to US gallons at 7.48 gallons per cubic foot, the figure the U.S. Geological Survey uses. Liters come from the NIST factor of 3.785412 liters per gallon. Round and oval areas use 0.785 (3.14 divided by 4) and kidney areas use 0.45 x (A + B) x length, the formulas in the San Diego County pool operator guide published by its Department of Environmental Health.

Treat the answer as a close estimate. Steps, benches, sun shelves and a sloped transition between the ends all change the true figure, and a water meter reading taken while the pool fills gives a measured figure instead of an estimate. Pool operator guides, including San Diego County’s, work from the same formula-based estimate.

Pool volume formulas by shape, and where each factor comes from

Every formula has the same two steps: work out the surface area, then multiply by average depth and by 7.48. The shape only changes the area step. A circle covers 3.14 x radius x radius, which is the same as 0.785 x diameter x diameter. An oval covers 3.14 x half the length x half the width, which is 0.785 x length x width. A kidney pool covers about 0.45 x (A + B) x length, where A and B are the widths across the two lobes.

You will see two shortcut numbers on other pool size calculator pages. Many use 7.5 in place of 7.48, including the San Diego County guide and the City of Akron sheet; the difference is 0.27%. Akron also uses 5.9 for round and oval pools, which is the 0.785 area factor already multiplied by a rounded gallons figure (0.785 x 7.48 is about 5.87).

How to measure your pool for a pool size calculator

1. Measure the water surface, not the deckRun a tape along the inside edge of the coping for length and width. Coping and deck width do not hold water.
2. Find the widest points on curved poolsFor a round pool, measure straight across through the center for the diameter. For a kidney, measure the full length plus the width across each lobe (A and B).
3. Read the depth at both endsPush a pole to the floor at the shallow end and at the deepest point and mark the water line. Many pools also have depth markers on the tile.
4. Convert inches to feetDivide inches by 12. A 54-inch water depth in an above-ground pool is 4.5 ft.
5. Split odd shapesMeasure an L-shape as two rectangles, and a pool with a round spa as a rectangle plus a circle, then add the volumes.
6. Check against a known numberIf your builder’s plans, the original permit or a fill-day water meter reading lists gallons, compare it with the calculator and use the documented figure.

Water level matters as much as the shell. A pool filled to the middle of the skimmer opening holds less than its nominal size suggests, and an above-ground pool with a 52-inch wall rarely holds 52 inches of water. The City of Akron table, for example, lists 2,975 gallons for a 12 ft round pool with a 48-inch wall, which matches the formula at about 3.5 ft of water (12 x 12 x 3.5 x 5.9 is 2,974).

Worked examples: how many gallons in a pool of each shape

Rectangle. A 16 x 32 ft pool that runs from 3.5 ft to 6 ft deep has a 4.75 ft average depth. 512 sq ft x 4.75 ft is 2,432 cubic feet, and 2,432 x 7.48 is about 18,191 gallons, or 68,862 liters. Akron’s table puts the same footprint at 17,300 gallons at 4.5 ft and 19,200 at 5 ft, so the answer sits where it should.

Round. A 24 ft round above-ground pool holding 4 ft of water covers 452.16 sq ft (0.785 x 24 x 24). That is 1,808.64 cubic feet, or about 13,529 gallons. Akron lists 13,594 gallons for the same pool with a 52-inch wall, the small gap coming from its 5.9 shortcut.

Oval. A 15 x 30 ft oval with 4 ft of water covers 353.25 sq ft and holds about 10,569 gallons. Akron’s 52-inch wall table lists 10,620 gallons for a 15 x 30 oval.

Kidney. A kidney pool 30 ft long with lobes 10 ft and 14 ft wide, 3.5 ft to 6 ft deep, covers 324 sq ft (0.45 x 24 x 30) and holds about 11,512 gallons. Measured as a plain 30 x 14 ft rectangle, the same pool would come out at 14,923 gallons, 30% too high, which is why the shape setting matters. Leslie’s free-form shortcut gives 11,770 gallons, 2% above the kidney formula.

For a bigger check, the San Diego County guide works a 30 x 50 ft pool that runs from 3 ft to 6 ft: 1,500 sq ft x 4.5 ft x 7.5 is 50,625 gallons. With 7.48 the same pool comes to 50,490 gallons.

How many gallons in a pool: standard sizes at a glance

If your pool matches a stock size, these published tables give the answer without a tape measure.

Read across to your average depth. A 16 x 32 ft pool holds 13,400 gallons at a 3.5 ft average and 21,100 gallons at 5.5 ft. A 20 x 40 ft pool holds 24,000 gallons at a 4 ft average and 30,000 at 5 ft. For the footprints these sizes come in, see our guide to standard pool sizes and the shapes in pool shapes.

Above-ground pools are sold by diameter and wall height, so the table lists both. An 18 ft round pool holds 7,646 gallons with a 48-inch wall and 8,602 gallons with a 52-inch wall, and a 24 ft round holds 11,895 and 13,594. Akron’s 48-inch figures for most sizes imply water about 3.5 ft deep, so measure your own water level if you dose by these numbers. For prices by size, see above ground pool cost.

Why your pool's volume matters: chemicals, pump, heat and water bills

Chemical dosing. Chemical doses are worked out from the volume of water: the San Diego County guide gives its volume formulas to help with “determining amount of chemicals to add to adjust pool water chemistry”. A dose based on a volume that is 30% too high puts in about 30% too much product. Before adjusting balance, read our guides on how to raise pH in a pool, how to lower pH and cloudy pool water.

Pump run time. Turnover is the time it takes the full volume to pass through the filter: volume divided by flow rate divided by 60 (San Diego County DEH). ENERGY STAR’s pool pump fact sheet calibrates the lowest pump speed to a 12-hour turnover. For the 18,191-gallon example that works out to about 25.3 gallons per minute.

Heating. One Btu warms one pound of water by 1 F (EIA), and a cubic foot of water weighs 62.3 lb at 70 F (USGS). The 16 x 32 ft example holds about 151,514 lb of water, so a 10 F rise needs about 1.52 MMBtu before any heat escapes. At 2025 US average delivered-heat prices of $18.06 per MMBtu for gas and $10.14 for a heat pump, that is about $27.36 and $15.36. Real seasons cost far more because evaporation, the largest source of pool energy loss according to DOE, keeps pulling heat out; see what it costs to heat a pool and the solar pool heater guide.

Filling and refilling. Water and sewer charges turn gallons into dollars. At October 2026 rates, filling 20,000 gallons costs $649.98 in Houston, where sewer is billed on the fill, and $180.61 in Phoenix, based on our study of the cost to fill a pool in 25 cities.

Evaporation and top-offs. Evaporation depends on surface area, not depth. Every inch lost from a 16 x 32 ft pool is about 319 gallons, and from a 15 x 30 ft pool about 280.5 gallons. NOAA pan data put a 15 x 30 ft pool in Las Vegas at about 23,444 gallons a year, more than the 18,191 gallons in the 16 x 32 ft example (pool evaporation rate).

Surface area: the other pool size number heaters, covers and solar use

Gallons drive chemicals and fill cost, but several kinds of equipment are sized on surface area, which the calculator’s first step already gives you. Three examples from federal guidance:

• Solar pool heaters: collector area of 50% to 100% of the pool’s surface area, according to the archived U.S. Department of Energy Energy Saver guide. Our solar pool heater guide turns that into panel counts.
• Heat pump heaters: DOE’s sizing rule is Btu per hour = pool area x temperature rise x 12 (DOE Energy Saver, archived).
• Covers: safety covers are ordered by the pool’s shape, length and width; see the pool safety cover guide for mesh, solid and automatic options.

If you are still choosing a size, volume also feeds the build budget: bigger shells mean more excavation, finish area and water. Our inground pool cost guide breaks down price by size, and local water costs differ widely; our city pages for Phoenix and Houston cover local rules and costs.

Related guides and data

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