How to measure for your pool volume project
- Pick your pool shape. Select Rectangle / Square for a standard in-ground or above-ground pool with straight sides. Select Round / Circular for a round above-ground pool — enter the diameter for both length and width. Select Oval for an oval above-ground pool — enter the full length and full width.
- Enter the size and depths. Type the length and width in feet. Then enter the shallow-end depth and the deep-end depth, both in feet. If your pool has a flat bottom at one depth, enter that same number for both shallow and deep.
- Read the gallon count and use it. The result shows total gallons, surface area, average depth, and cubic feet. Use the gallon count to dose chemicals, size your pump and filter, estimate fill time, and budget for heating — your pool's volume is the single number that ties all of these together.
How the pool volume calculator works
Pool volume comes down to footprint area × average depth × a unit conversion. First, find the surface area: for a rectangle it's length × width; for a round or oval pool it's length × width × 0.7854 (which is π ÷ 4, the ratio of a circle's area to the square it fits inside). Second, find the average depth by adding the shallow-end and deep-end depths and dividing by 2. Third, multiply surface area × average depth to get cubic feet of water. Finally, multiply by 7.48 gallons per cubic foot — that's the unit conversion from cubic feet to US gallons. Worked example: a 32 × 16 ft rectangle with a 3 ft shallow end and 8 ft deep end. Surface area = 32 × 16 × 1 = 512 sq ft. Average depth = (3 + 8) ÷ 2 = 5.5 ft. Cubic feet = 512 × 5.5 = 2,816 cu ft. Gallons = 2,816 × 7.48 ≈ 21,063 gallons.
Which type are you estimating?
Rectangular or square pool
The most common shape for in-ground pools. The full length and width contribute 100% to the surface area, so the shape factor is 1. Measure along the waterline, not the coping, for the most accurate result.
Enter: Shape: Rectangle / Square — enter length, enter width
Round above-ground pool
A circle covers only π/4 ≈ 78.54% of the square that would surround it, so the calculator applies a 0.7854 factor to the footprint. Enter the pool's diameter for both the length and width fields. For example, a 24 ft round pool at an average depth of 4 ft holds about 13,500 gallons.
Enter: Shape: Round / Circular — enter diameter for both length and width
Oval above-ground pool
An oval uses the same 0.7854 shape factor as a round pool. Enter the full length and the full width (the widest point across the short axis). A 15 × 30 ft oval at 4 ft average depth holds about 10,600 gallons.
Enter: Shape: Oval — enter full length and full width
Flat-bottom pool (uniform depth)
Kiddie pools, therapy pools, and many above-ground pools have the same depth from end to end. Enter that single depth for both the shallow-end and deep-end fields so the average equals the actual depth.
Enter: Any shape — enter the same value for shallow-end and deep-end depth
Sloped-bottom in-ground pool
Most residential in-ground pools slope from a shallow end (typically 3–3.5 ft) to a deep end (5–8 ft or more). The average-depth formula, (shallow + deep) ÷ 2, handles a single linear slope accurately. If your pool has a second slope or a hopper bottom, split it into sections, calculate each, and add the gallons together.
Enter: Any shape — enter actual shallow-end depth and deep-end depth separately
Tips & ways to save
- Your gallon count is the starting point for every chemical dose — shock, chlorine, algaecide, and pH adjusters are all dosed per 10,000 gallons, so being off by even 20% throws your chemistry.
- Pump and filter systems are rated by gallons per hour (GPH) or gallons per minute (GPM). The standard target is to turn your entire pool volume over at least once every 8 hours — divide your gallons by 8 to find the minimum GPH your pump needs.
- To estimate fill time, look up your home's hose flow rate (a standard 5/8-in garden hose runs about 9–17 gallons per minute at normal pressure). Divide your pool gallons by GPM to get minutes, then divide by 60 for hours.
- Above-ground pools should be filled a few inches below the top rail, not to the brim — so your actual water volume will be slightly less than the wall-height calculation suggests. Use the depth of water, not the wall height, when entering numbers.
- Pool volume changes seasonally. If you drain and refill for winter, or top off after evaporation, recalculate with the current water depth rather than the pool's full capacity — this matters especially for shock treatments.
Gallons in a round above-ground pool
| Pool size (diameter) | 48-in wall (~4 ft water) | 52-in wall (~4.4 ft water) |
|---|---|---|
| 12 ft round | ~3,400 gal | ~3,700 gal |
| 15 ft round | ~5,300 gal | ~5,800 gal |
| 18 ft round | ~7,600 gal | ~8,400 gal |
| 21 ft round | ~10,400 gal | ~11,400 gal |
| 24 ft round | ~13,500 gal | ~14,900 gal |
| 27 ft round | ~17,100 gal | ~18,800 gal |
| 30 ft round | ~21,200 gal | ~23,300 gal |
Above-ground pools fill a few inches below the rail, so water depth is a bit less than the wall height — these assume about 4 ft (48-in wall) and 4.4 ft (52-in wall) of water. For an exact number, enter the diameter for both length and width above.
Frequently asked questions
How many gallons is a 24-foot round pool?
How many gallons is an 18-foot or 15-foot round pool?
How do I calculate the gallons in my pool?
How many gallons is a 12-foot round pool?
Why do I need to know my pool's volume in gallons?
How do I measure the depth of my pool for the calculator?
Sources
Related calculators
Reviewed by the BackyardCalc editorial team. Figures are computed from the formula above and checked against manufacturer yields.