Round Pool Gallons Calculator (Inground & Above Ground)

Calculator

A 24 ft round pool with 4 ft of water holds 13,536 gallons. As an above-ground frame pool with a 52 in wall at 90% fill, it holds about 12,274 gallons.

Choose "Water depth" for an inground pool or any pool where you can measure the water directly. Choose "Above-ground wall height" if you know only the wall height from the box. The calculator assumes 90% fill unless you change it, and it applies the frame or inflatable correction described below.

Formula: diameter² × depth × 5.9

The area of a circle is π × radius², or π/4 × diameter². One cubic foot of water is 7.48 US gallons. Put them together: π/4 × 7.48 = 5.875, which rounds to the familiar 5.9:

Measure the diameter across the widest point, inside the wall, in feet.
Measure the water depth in feet (inches ÷ 12). For a sloped floor, use the average depth (see the sections below).
Multiply: diameter × diameter × depth × 5.9. For liters, multiply gallons by 3.785.

Example: 18 ft pool, 4 ft deep: 18 × 18 × 4 × 5.875 = 7,614 gallons. Using 5.9 gives 7,646, a 0.4% difference that doesn't matter for dosing. For metric measurements, liters = 785 × diameter² × depth in meters.

Above-ground pools: wall height vs water depth

Box sizes give the wall height, but the water never reaches the top: it stops around the skimmer, and manufacturers such as Intex rate capacity at 80% or 90% of the wall. A 52 in wall at 90% means about 46.8 in (3.9 ft) of water. On top of that, the nominal diameter is usually the outside of the frame, and inflatable walls lean in. We compared 26 above-ground models with their manufacturer capacities. The median real volume was 0.933 of the geometric volume. That's why the calculator multiplies by 0.93 for frame pools and 0.87 for inflatable-ring pools unless you choose "Exact geometry". If you know your model, the above-ground pool gallons chart has manufacturer capacities for 33 pools.

Chart: 12–33 ft

Gallons by average water depth, from the formula. Use it for inground pools, or for above-ground pools where you measured the water depth yourself.

Round pool gallons by diameter and average water depth
Diameter	3.5 ft	4 ft	4.5 ft	5 ft	6 ft
12 ft	2,961	3,384	3,807	4,230	5,076
15 ft	4,627	5,288	5,949	6,610	7,932
16 ft	5,264	6,016	6,768	7,520	9,024
18 ft	6,662	7,614	8,566	9,518	11,421
20 ft	8,225	9,400	10,575	11,750	14,100
21 ft	9,068	10,364	11,659	12,955	15,546
24 ft	11,844	13,536	15,228	16,921	20,305
27 ft	14,991	17,132	19,274	21,415	25,698
28 ft	16,122	18,425	20,728	23,031	27,637
30 ft	18,507	21,151	23,795	26,438	31,726
33 ft	22,393	25,592	28,791	31,990	38,388

US gallons, exact geometry (π/4 × D² × depth × 7.48). Each linked size has its own page with models, wall heights, and starting doses.

Sloped round inground pools

If the floor slopes evenly from one side to the other, the average depth is (shallow + deep) ÷ 2. A 20 ft round pool going from 3.5 ft to 6 ft averages 4.75 ft and holds about 11,163 gallons.

If the floor is flat for a while and then drops, average the sections by their length across the pool. Example for an 18 ft pool: 12 ft of floor sloping from 3.5 to 4 ft, then 6 ft dropping from 4 to 7 ft. Average depth = (12 × 3.75 + 6 × 5.5) ÷ 18 = 4.33 ft, so the pool holds about 8,249 gallons. This length-weighted average is an approximation for a circle, because the middle of the pool has more area than the edges. Expect a few percent of error. If you need more accuracy, the pool volume calculator handles other shapes, and a salt or stabilizer rise test measures the real volume.

FAQ

How many gallons in a round pool?

Diameter² × average water depth × 5.9. Common sizes range from about 3,000 gallons (12 ft, 3.5 ft deep) to over 25,000 gallons (33 ft, 4 ft deep).

How to calculate round pool gallons?

Measure the inside diameter and the water depth in feet, multiply diameter × diameter × depth, then multiply by 5.9. For a sloped floor, use the average depth.