How Many Gallons Is My Pool?
Your pool's volume is its surface area times its average depth, times 7.48 to get gallons. Here is the formula, a chart of common pool sizes in gallons, and how to handle a sloping floor.
By the Calculate My Reno Team / Published
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Your pool holds its surface area times its average depth. In US units that gives cubic feet, and there are 7.48 gallons in a cubic foot:
gallons = surface area (sq ft) × average depth (ft) × 7.48
rectangle surface area = length × width
round surface area = π × (diameter ÷ 2)²
Skip the math
Enter your pool shape, size and depth in the pool volume calculator and it returns the volume in US gallons, imperial gallons, litres and cubic metres at once, including a shallow-and-deep-end average. The rest of this guide is the charts and the why.
Common rectangular pool sizes in gallons
These are inground rectangular pools at about a 5 ft average depth. A pool with a deeper end holds more, so treat these as a baseline and adjust for your own average depth:
| Pool size | Surface area | US gallons | Litres |
|---|---|---|---|
| 12 × 24 ft | 288 sq ft | ~10,800 | ~40,800 |
| 14 × 28 ft | 392 sq ft | ~14,700 | ~55,600 |
| 15 × 30 ft | 450 sq ft | ~16,800 | ~63,700 |
| 16 × 32 ft | 512 sq ft | ~19,200 | ~72,500 |
| 18 × 36 ft | 648 sq ft | ~24,200 | ~91,800 |
| 20 × 40 ft | 800 sq ft | ~30,000 | ~113,400 |
Common round pool sizes in gallons
Round above-ground pools usually sit at about 4 ft of water (the water line is roughly 6 inches below a 52-inch wall). For the full chart by diameter and depth, see how many gallons in a round pool:
| Round pool | US gallons | Litres |
|---|---|---|
| 15 ft round | ~5,300 | ~20,000 |
| 18 ft round | ~7,600 | ~28,800 |
| 21 ft round | ~10,400 | ~39,200 |
| 24 ft round | ~13,500 | ~51,200 |
| 27 ft round | ~17,100 | ~64,800 |
| 30 ft round | ~21,200 | ~80,000 |
Shallow end and deep end
If your pool has a shallow end and a deep end with an evenly sloping floor, the average depth is just the two end depths added and halved:
average depth = (shallow + deep) ÷ 2
A pool running from 3 ft to 8 ft averages 5.5 ft. Use that average in the formula, not the deep-end figure. If the deep end is a small diving hollow rather than an even slope, the true average is a touch less, so the even-slope figure is a safe over-estimate.
Worked example
A 16 by 32 ft pool with a 3 ft shallow end sloping to a 7 ft deep end:
surface area = 16 × 32 = 512 sq ft
average depth = (3 + 7) ÷ 2 = 5 ft
volume = 512 × 5 = 2,560 cu ft
gallons = 2,560 × 7.48 = about 19,150 US gallons
So roughly 19,000 gallons - the number to dose chemicals against. To see how long that takes to fill, read how long does it take to fill a pool.
Frequently asked questions
How do I figure out how many gallons my pool is?
Multiply the surface area in square feet by the average depth in feet to get cubic feet, then multiply by 7.48 for US gallons. A 16 by 32 ft pool averaging 5 ft deep is 512 sq ft times 5 = 2,560 cu ft, which is about 19,150 gallons. For a round pool the surface area is pi times the radius squared. Enter your size in the calculator and it does the arithmetic and the gallon conversion for you.
How many gallons is a 16x32 pool?
A 16 by 32 ft rectangular pool holds about 19,200 US gallons at a 5 ft average depth, or about 21,100 gallons if it averages 5.5 ft. The exact figure depends on your average depth, so a pool with a deep end holds more than one of uniform depth. Use 7.48 gallons per cubic foot: 16 × 32 × average depth × 7.48.
How many gallons is a 18x36 pool?
An 18 by 36 ft rectangular pool holds about 24,200 US gallons at a 5 ft average depth, and around 26,600 gallons at 5.5 ft. Multiply 18 × 36 = 648 sq ft by your average depth in feet and then by 7.48 to get gallons.
Why does the average depth matter so much?
Volume is area times average depth, so the depth scales the whole answer. A pool with a 3 ft shallow end and a 7 ft deep end averages 5 ft if the floor slopes evenly, and you use that 5 ft, not the deepest point. Getting the average depth wrong is the most common reason a gallon estimate is off, which then throws out every chemical dose.
How accurate does the gallon figure need to be?
Close is fine. Sanitizer and balancing chemicals are dosed per 10,000 gallons, so being within a few percent is plenty for everyday pool care. It is better to round the volume up than down, because an over-estimate means you slightly under-dose, which is safer and cheaper to correct than over-dosing.