Pool Volume Calculator
Work out how many gallons your pool holds. Pick your shape, enter the dimensions in feet, and the calculator does the rest, showing liters and surface area too.
Freeform pools use the industry 0.45 multiplier approximation, so treat the result as within about 10 percent. Constant-depth pools: enter the same depth in both fields.
How pool volume is calculated
Pool volume is surface area multiplied by average depth, converted to gallons. One cubic foot of water is 7.48 gallons, so every formula below ends with that multiplier:
Round: 3.14 x (diameter / 2)² x average depth x 7.48
Oval: 3.14 x (length / 2) x (width / 2) x average depth x 7.48
Kidney/freeform: 0.45 x (width A + width B) x length x average depth x 7.48
Average depth for a sloped pool is simply (shallow depth + deep depth) / 2. If your pool floor has a distinct shallow shelf and a deep hopper rather than an even slope, split the pool into two rectangles, calculate each, and add them for a tighter number.
Worked example: a 16x32 pool
Take the most common inground size in the US, a 16 by 32 foot rectangle with a 3.5 foot shallow end and 8 foot deep end:
- Surface area: 16 x 32 = 512 sq ft
- Average depth: (3.5 + 8) / 2 = 5.75 ft
- Cubic feet: 512 x 5.75 = 2,944
- Gallons: 2,944 x 7.48 = about 22,000 gallons
That 22,000-gallon figure is the number you will reuse constantly: in the salt calculator when starting a salt water generator, in the chlorine calculator after a rainstorm, and in the chemical calculator when alkalinity drifts.
Common pool sizes in gallons
Quick reference for typical sizes, assuming a 3.5 to 8 foot slope (average depth 5.75 ft) for inground and constant 4 ft for above-ground:
- 12 x 24 ft inground: about 12,400 gallons
- 14 x 28 ft inground: about 16,900 gallons
- 16 x 32 ft inground: about 22,000 gallons
- 18 x 36 ft inground: about 27,900 gallons
- 20 x 40 ft inground: about 34,400 gallons
- 15 ft round above-ground (4 ft): about 5,300 gallons
- 24 ft round above-ground (4 ft): about 13,500 gallons
Tips for an accurate result
- Measure water dimensions, not deck-to-deck. Coping overhangs add phantom feet.
- Use actual water depth, not wall height, above-ground pools filled to 6 inches below the rim lose real volume.
- When in doubt, round volume down slightly. Underdosing chemicals and retesting is safer than overdosing.
Frequently asked questions
How many gallons is a 16x32 pool?
A 16 by 32 foot rectangular pool with a 3.5 foot shallow end and 8 foot deep end holds about 22,000 gallons: 16 x 32 x 5.75 (average depth) x 7.48 = 22,020 gallons. A constant 4 foot depth version holds about 15,300 gallons.
How do I measure average depth?
For a pool with a constant slope, add the shallow end depth to the deep end depth and divide by two. A 3 foot shallow end and 8 foot deep end gives an average depth of 5.5 feet. If your pool has a long shallow section and a short deep hopper, this slightly overestimates volume.
Why does pool volume matter?
Every chemical dose is proportional to water volume. If your volume estimate is off by 20 percent, every chlorine, salt, acid, and stabilizer dose you ever add is off by 20 percent too. Calculate it once and write it down.
How accurate is the kidney or freeform estimate?
The standard industry approximation (0.45 times the sum of the two widths times length) is typically within about 10 percent for gently curved pools. For very irregular shapes, break the pool into simple sections, calculate each, and add them.