Pool Volume Calculator – How Many Gallons Is My Pool?
This pool volume calculator tells you how many gallons of water your pool holds: pick the shape, enter length, width and depth, and you instantly see gallons and liters. You need that number to dose chemicals, size a heater or pump – and you also get the time to fill the pool with a garden hose.
Example: Pool shape: rectangular · Length (round pool: diameter) 26 ft · Width 13 ft · Depth at shallow end 3.5 ft · Depth at deep end 6 ft · Water flow when filling 5 gpm · Circulation pump flow rate 40 gpm → Pool volume: 12,010 gallons (45,463 liters). Source: Leslie’s – How to calculate pool volume (rectangular, round, oval, kidney; average depth). Updated: .
How it is calculated
How pool volume is calculated
It is always water surface area × average depth. The area depends on the shape:
- Rectangular: length × width. A 26 × 13 ft pool has 338 sq ft.
- Round: π × (diameter ÷ 2)². A 15 ft pool covers about 177 sq ft.
- Oval: π ÷ 4 × length × width (an ellipse).
- Kidney: 0.45 × (width A + width B) × length – the common rule of thumb in the pool trade, where A and B are the two widest points.
The average depth is the mean of the shallow and deep ends. Example: a 26 × 13 ft pool that is 3.5 ft at the shallow end and 6 ft at the deep end averages 4.75 ft. That is 338 × 4.75 ≈ 1,606 cubic feet, and one cubic foot holds 7.48 US gallons, so the pool holds about 12,000 gallons (45,500 liters).
Water depth, not wall height
Use the depth the water actually reaches – in most pools with a skimmer, about the middle of the skimmer opening rather than the top of the wall. For above-ground pools the advertised wall height is usually greater than the recommended water level.
Filling and circulation
Volume and flow give the fill time: 12,000 gallons at 5 gallons per minute take 40 hours. Divide the volume by the pump flow rate to get the turnover time – 12,000 gallons at 40 gpm is 5 hours for the whole pool to pass through the filter once. To estimate what the pump costs to run, use the electricity cost calculator; for other shapes the volume calculator helps.
Limits
Free-form pools with irregular curves, benches or sloped walls can only be estimated roughly; split them into simple sections and add the volumes. For chemicals, always follow the manufacturer’s instructions on the label.
Frequently asked questions
How do I calculate the volume of a rectangular pool?
Length × width × average depth × 7.48 gives gallons. A 26 × 13 ft pool with 4.75 ft average depth holds about 12,000 gallons.
How do I calculate the volume of a round pool?
π × (diameter ÷ 2)² × depth × 7.48. A 15 ft round pool with 4 ft of water holds about 5,300 gallons.
How do I calculate the gallons in an oval pool?
π ÷ 4 × length × width × average depth × 7.48. An oval pool of 20 × 10 ft with 4 ft average depth holds about 4,700 gallons.
How do I find the average depth?
Add the shallow and deep depths and divide by 2. With 3.5 ft and 6 ft that is 4.75 ft. For a flat-bottom pool it is simply that depth.
How long does it take to fill a pool?
Divide the gallons by the flow rate in gallons per minute. 12,000 gallons at 5 gpm is 2,400 minutes, or 40 hours.
Sources and legal basis
- Leslie’s – How to calculate pool volume (rectangular, round, oval, kidney; average depth)
- Pool Research – Pool volume calculator (formulas and multipliers by pool shape)
- NIST SP 811, Appendix B – conversion factors (foot, gallon, cubic foot, liter)
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