How this calculator gets gallons
Volume is surface area times average depth. Feet are converted with the international foot, 1 ft = 0.3048 m. One US gallon is 231 cubic inches, which is 0.003785411784 cubic meters, so one cubic foot is 7.48051948… US gallons. Rectangle, round, ellipse, straight-sided oval, and kidney each use a different area. Kidney area uses the estimate (widest width + second width) × length × 0.45.
Example
A 32 × 16 ft rectangular pool, 3.5 ft at the shallow end and 6 ft at the deep end, has an average depth of 4.75 ft. That is 2,432 cubic feet: 18,193 US gal, 68,867 L, 68.87 m³, and 15,149 imperial gal.
Why pool volume matters
Chlorine, shock, pH adjusters, alkalinity increaser, and salt are all dosed from the volume of water. A wrong gallon count is a common reason a pool goes cloudy or harsh. Volume also sets pump runtime: gallons divided by pump flow in gallons per minute is the turnover time, and it is the starting point for what a refill costs on a water bill.
Chlorine and salt dosing
One ppm is one milligram per liter. Raising free chlorine by 1 ppm in 10,000 US gallons takes about 37.85 grams of available chlorine. That is about 10.2 fl oz of 12.5% liquid chlorine, or about 2.1 oz of 65% calcium hypochlorite. Salt systems often run at 2,700-3,400 ppm. Check the cell manual. Raising 10,000 US gallons from 0 to 3,200 ppm takes about 267 lb of pool salt.
Tips for accurate measurements
- Measure the water surface, not the coping, and the water depth, not the wall height.
- Use decimal feet. 3 ft 6 in is 3.5 ft, not 3.6 ft.
- Above ground pools are often filled to about 6 inches below the top rail.
- A free-form pool can be split into rectangles and circles. Calculate each part and add the volumes.
Filling time and pump turnover
Divide the gallons by the hose flow. A garden hose often delivers about 9-17 gallons per minute, so an 18,000-gallon pool can take roughly 18-33 hours. For filtration, many pools aim to turn the full volume over at least once a day. Required pump flow in gallons per minute is gallons divided by (hours of run time × 60). For 18,000 gallons in 8 hours, that is about 38 gallons per minute.
Frequently asked questions
How many gallons are in a 24 ft round above ground pool?
At 48 inches of water, a 24 ft round pool holds 13,536 US gallons. Many charts round that figure to about 13,500.
How do I calculate pool volume in liters?
Multiply length, width, and average depth in meters to get cubic meters, then multiply by 1,000. One US gallon is 3.785411784 liters.
How much chlorine do I add per 10,000 gallons?
About 10.2 fl oz of 12.5% liquid chlorine raises free chlorine by 1 ppm in 10,000 US gallons. Always follow the product label.
How much salt does a salt water pool need?
Most systems target 2,700-3,400 ppm. From zero, 10,000 US gallons needs about 225-284 lb of salt.
What is the average depth of a pool?
For a straight slope and constant width, add the shallow and deep ends and divide by 2. A long shallow shelf should be split into sections instead of one average.