How to use the pool volume calculator
- Choose the pool shape: rectangular, round, oval or kidney (an approximation).
- Enter the dimensions in feet that the shape asks for: length and width, a diameter, or the two widths of a kidney pool.
- Enter the depth at the shallow end and the depth at the deep end. For a flat bottom, enter the same number twice.
- Read the volume in gallons and liters. Add a water price per 1,000 gallons for a rough fill cost.
Formula
Rectangular area = length x width
Round area = 3.14159 x (diameter / 2)^2
Oval area = 3.14159 / 4 x length x width
Kidney area (approximation) = 0.45 x (width A + width B) x length
Average depth = (shallow depth + deep depth) / 2
Cubic feet = area x average depth; gallons = cubic feet x 7.48052; liters = gallons x 3.785411784
One cubic foot holds 7.48052 US gallons. The average depth method takes the simple midpoint of the two depths, which is right only for a floor that slopes evenly from one end to the other.
Worked example: a 24 ft by 12 ft rectangular pool, 3 ft to 6 ft deep
The area is 24 x 12 = 288 sq ft. The average depth is (3 + 6) / 2 = 4.5 ft.
Volume is 288 x 4.5 = 1,296 cubic feet.
In gallons that is 1,296 x 7.48052 = 9,695 gallons, and in liters 9,694.75 x 3.785411784 = 36,699 liters.
At $4.50 per 1,000 gallons, filling the pool once costs about $43.63 in water, before any sewer or service charges.
The average depth method
Averaging the shallow and deep ends is the standard quick approach and works for a pool whose floor slopes steadily. Many real pools do not. A pool with a flat shallow shelf, a steep drop and a deep hopper holds a different volume than the simple average predicts, and the result can be off by a large margin. If your pool has a complicated floor, split it into sections and run the calculator for each, or ask the builder for the design volume.
Water level and measurement
Pools are not filled to the brim. The water line is usually several inches below the top of the wall, so if you measured the full wall height the answer will be a little high. Measure the depth at the water line when you can. Measure length and width at the water line too, because walls often slope or curve inward.
Why volume matters
Chemical dosing, heater sizing and pump turnover all depend on volume, and an error in the volume carries into each of them. Treat this result as a good estimate, then follow product labels and, where in doubt, a pool professional. If you are sizing a pump or heater, the electricity cost calculator can help you estimate running costs once you know the watts.
Assumptions and limits
- Average depth is the simple mean of the shallow and deep depths, which assumes an even slope.
- The kidney shape uses a common approximation (0.45 x the sum of the two widths x the length). Real kidney pools differ.
- Gallons are US gallons at 7.48052 per cubic foot. Liters use 3.785411784 per US gallon.
- Walls are treated as vertical and the water line as level with the full depth you enter.
- The fill cost uses only the price per 1,000 gallons you enter and leaves out sewer charges, fees and evaporation.
Frequently asked questions
How many gallons are in a cubic foot?
A cubic foot holds 7.48052 US gallons. Multiply your pool volume in cubic feet by that number to get gallons.
How do I find the volume of a round pool?
Compute the area as 3.14159 times the radius squared, where the radius is half the diameter. Multiply by the average depth to get cubic feet, then by 7.48052 for gallons.
Is the kidney pool result exact?
No. It uses a commonly quoted approximation that can differ from the true volume by several percent, so treat it as a rough estimate and confirm with your builder.
What depth should I enter for a flat-bottom pool?
Enter the same depth in both the shallow and deep boxes. The average is then equal to that depth.
Why is my pool shape not listed?
Irregular pools can be split into rectangles, circles and ovals. Run each part separately and add the gallons together to estimate the total.