Pool Volume Calculator

A standard 16 by 32 foot rectangular pool with an average depth of 5 feet holds about 19,150 gallons. Enter your own measurements below and the figure updates as you type. Everything else on this site, chlorine dosing, fill cost, pump energy, runs off this number.

Common pool sizes and their volumes

If you cannot get to the pool right now, find the closest match. These are calculated with the same formulas the calculator uses, so they are consistent with your own result rather than rounded trade estimates.

Pool size	Average depth	Volume
12 x 24 ft rectangle	5 ft	10,772 gallons
14 x 28 ft rectangle	5 ft	14,662 gallons
16 x 32 ft rectangle	5 ft	19,150 gallons
18 x 36 ft rectangle	5 ft	24,237 gallons
20 x 40 ft rectangle	5.5 ft	32,914 gallons
21 ft round	4 ft	10,364 gallons
24 ft round	4 ft	13,536 gallons

How pool volume is calculated

Surface area multiplied by average depth gives you cubic feet. One cubic foot of water is 7.48052 US gallons. That single conversion is the whole thing; the only part people get wrong is average depth.

rectangle   length x width x average depth x 7.48052
round       3.1416 x radius squared x average depth x 7.48052
oval        length x width x 0.785 x average depth x 7.48052
freeform    length x width x 0.85 x average depth x 7.48052

The 0.785 in the oval formula is pi divided by four, which is the ratio of an ellipse to the rectangle that would contain it. The 0.85 for freeform shapes is a working estimate rather than geometry, so treat a freeform result as approximate and lean toward over-dosing chemicals slightly rather than under-dosing.

A worked example

Take a 16 by 32 foot rectangular pool that is 3 feet deep at the shallow end and 7 feet at the deep end.

1. Average depth: (3 + 7) divided by 2 = 5 feet
2. Surface area: 16 x 32 = 512 square feet
3. Cubic feet: 512 x 5 = 2,560
4. Gallons: 2,560 x 7.48052 = 19,150

Why average depth matters more than maximum depth

Using the deep end figure instead of the average is the second most common mistake, and it is worse than the wall measurement error. On the pool above, using 7 feet instead of 5 gives 26,810 gallons, overstating the volume by forty percent. Every chemical dose calculated from that number is forty percent too high.

If your pool has a long flat shallow section and a short deep end, the simple average overstates things slightly. In that case measure at three or four points along the length and average those instead.

What if the pool is an irregular shape

Break it into sections you can measure. A kidney shape is usually two overlapping circles or a rectangle plus a half circle. Calculate each piece separately, add the results, then subtract any overlap. That is more accurate than applying the freeform multiplier to a single length and width.

If you cannot face the arithmetic, use the freeform setting and accept that the answer is within about ten percent. For routine chlorine maintenance that is close enough. For a one-off treatment where the dose matters, measure properly.

Should an attached spa be included

Only if the water actually circulates between them. A spa plumbed into the same system with a shared pump and filter is part of the same body of water, so measure it and add it. A standalone hot tub with its own pump and its own chemistry is a separate problem and should not be added here.

A typical attached spa adds between 400 and 800 gallons, which is enough to matter when you are shocking the pool but not enough to worry about for weekly chlorine.

What to do with the number

Write it on the inside of the equipment cabinet door. You will need it every time you add anything to the water, and the alternative is re-measuring or guessing, which is how people end up with cloudy water and a chlorine reading that will not move.

Chlorine dosing, fill cost and pump energy calculators are in progress. When they land, your volume will carry across to them automatically so you are not asked for it twice.