THE NUMORIX GUIDE
How to use the Pool Volume Calculator
Last reviewed September 14, 2026
What this calculator does
For a rectangular pool, the engine calculates cubic feet as length x width x average depth.
Formula and method
For a rectangular pool, the engine calculates cubic feet as length x width x average depth. For a circular pool, the UI's length field is the diameter and the engine calculates pi x (diameter / 2)^2 x depth. It converts cubic feet to gallons with 7.48052 gallons per cubic foot and gallons to liters with 3.78541 liters per gallon, rounding displayed volume to whole gallons and liters and cubic feet to two decimals.
Variables and inputs
Choose Rectangular or Circular. Rectangular inputs are length, width, and average depth in feet; circular inputs are diameter and average depth in feet, with the width field hidden. Depth is an average water depth, not necessarily the deepest point.
Worked example
For a rectangular pool 20 ft long, 10 ft wide, and 5 ft deep, cubic volume is 20 x 10 x 5 = 1,000.00 cubic ft. Gallons are 1,000 x 7.48052 = 7,480.52, displayed as 7,481 gal, and liters are displayed as about 28,317 L.
How to interpret the result
The result estimates the water volume of the selected idealized shape. Use the gallon value for a rough fill or chemical-volume reference, and use average depth when the pool floor is not level.
Common mistakes to avoid
Enter the circular pool's diameter, not its radius, because the engine divides the field by two. Keep all dimensions in feet, and use an average water depth rather than multiplying by only the deepest section.
Assumptions and limitations
The formulas do not model steps, benches, coves, sloped bottoms, rounded corners, freeboard, displacement, or changing water level. Whole-number output hides some precision, and chemical dosing should follow the product label and a measured pool volume when the shape is irregular.