The pool volume calculator works out how much water a rectangular, round or oval pool holds, in gallons, cubic feet and liters, from its size and its water depth, and how long it takes to fill at a flow you enter.
It uses plane geometry for the water's surface and the National Institute of Standards and Technology's conversion factors for the units: a cubic foot holds 7.48052 U.S. gallons and 28.31685 liters.
How to use it
- 01
Pick the shape
Rectangle, round, oval or oval with straight sides. A pool with rounded corners is close to a rectangle. The oval option is a true ellipse, measured across its longest and widest points; an oval with two straight sides and a half circle at each end is the straight-sided option.
- 02
Measure the water, not the walls
Length and width in feet across the water, or the diameter of a round pool, and the depth of the water itself at the shallow and deep ends, the same number twice for a flat floor: the water line sits below the top of the wall.
- 03
Add a fill flow if you want the time
Gallons a minute from the hose or fill line. Timing a bucket of known size gives it: a 5-gallon bucket filled in 30 seconds is 10 gallons a minute.
- 04
Price the water at your rate
Enter your water rate per 1,000 gallons or per 100 cubic feet, whichever your bill uses, and the calculator multiplies. No rate is filled in.
How the math works
Water surface
Rectangle: length × width. Round: π × (diameter ÷ 2)². Oval: π × (length ÷ 2) × (width ÷ 2). Oval with straight sides: (length − width) × width + π × (width ÷ 2)². A 32 × 16 ft rectangle is 512 sq ft, a 24 ft round pool 452 sq ft, and a 30 × 15 ft oval 353 sq ft as an ellipse but 402 sq ft with straight sides.
Volume
Cubic feet = surface × average depth, where the average depth is (shallow + deep) ÷ 2: right for a floor that slopes evenly from end to end. The 32 × 16 ft pool, 3½ ft to 6 ft deep, averages 4.75 ft and holds 2,432 cubic feet.
Gallons and liters
NIST puts a cubic foot at 2.831 685 × 10⁻² cubic meters and a U.S. gallon at 3.785 412 × 10⁻³, so a cubic foot is 7.48052 gallons and 28.31685 liters. The example holds 18,193 gallons.
Time to fill
Hours = gallons ÷ gallons a minute ÷ 60. At 10 gallons a minute, the example takes 30.3 hours.
Where the number goes wrong
- Using the wall height of an above-ground pool. The water line is below the top of the wall, and the volume follows the water.
- Averaging a floor that does not slope evenly. A deep end with a flat bottom or a bowl holds a different volume from a straight slope; split the pool into sections and add them.
- Measuring an oval across the outside of its frame. Measure the water.
- Mixing inches and feet. Every input is in feet: 6 inches is 0.5 ft.
Questions people ask
How many gallons are in a 24-foot round pool?
At 4 ft of water, about 13,536 gallons: π × 12² × 4 = 1,810 cubic feet, times 7.48052.
How many gallons are in a 16 × 32 pool?
About 18,193 gallons with water 3½ ft deep at one end and 6 ft at the other: 512 sq ft × 4.75 ft = 2,432 cubic feet.
How many gallons are in a cubic foot?
7.48052 U.S. gallons, from NIST's conversion factors; a cubic foot is also 28.31685 liters.
Does the volume decide whether a pool needs a permit?
Under some codes it is one of the lines. The model residential code exempts only a prefabricated pool less than 24 inches deep, with no volume in it, and Los Angeles a pool no deeper than 24 inches with no more than 250 square feet of water surface. The model code for other buildings adds a cap: a prefabricated pool at a house is exempt only under 24 inches deep, at no more than 5,000 gallons and entirely above ground. The pool permit brief sets out each city's lines.