Pool sizes in gallons
Common pools and what they hold. Inground sizes are shown at three average depths (3.5 ft is a shallow play pool, 4.5 ft a 3-to-6 ft slope, 5.5 ft a 3-to-8 ft diving pool). Above-ground figures match the pool-trade capacity charts, which assume 3.5 ft of water in a 48 in wall, 4 ft in a 52 in wall and 4.5 ft in a 54 in wall.
| Pool | 3.5 ft avg | 4.5 ft avg | 5.5 ft avg |
|---|---|---|---|
| 12 × 24 ft rectangle | 7,540 | 9,690 | 11,850 |
| 14 × 28 ft rectangle | 10,260 | 13,200 | 16,130 |
| 15 × 30 ft rectangle | 11,780 | 15,150 | 18,510 |
| 16 × 32 ft rectangle | 13,410 | 17,240 | 21,070 |
| 18 × 36 ft rectangle | 16,970 | 21,810 | 26,660 |
| 20 × 40 ft rectangle | 20,950 | 26,930 | 32,910 |
| 25 × 50 ft rectangle | 32,730 | 42,080 | 51,400 |
| Pool | 48 in wall | 52 in wall | 54 in wall |
|---|---|---|---|
| 12 ft round | 2,970 | 3,400 | 3,820 |
| 15 ft round | 4,650 | 5,310 | 5,970 |
| 18 ft round | 6,690 | 7,650 | 8,600 |
| 21 ft round | 9,110 | 10,410 | 11,710 |
| 24 ft round | 11,890 | 13,590 | 15,290 |
| 27 ft round | 15,050 | 17,200 | 19,350 |
| 30 ft round | 18,590 | 21,240 | 23,890 |
| 33 ft round | 22,490 | 25,700 | 28,910 |
| 12 × 24 ft oval | 5,950 | 6,800 | 7,650 |
| 15 × 30 ft oval | 9,290 | 10,620 | 11,950 |
| 16 × 32 ft oval | 10,570 | 12,080 | 13,590 |
| 18 × 33 ft oval | 12,270 | 14,020 | 15,770 |
| 18 × 38 ft oval | 14,120 | 16,140 | 18,160 |
| 21 × 41 ft oval | 17,780 | 20,320 | 22,860 |
How to calculate pool volume
- Measure the length and width in feet, or the diameter of a round pool, at the water line.
- Average the depth. Shallow end plus deep end, divided by two. A 3 ft to 8 ft pool averages 5.5 ft.
- Multiply by the factor for your shape.
Rectangle: length × width × average depth × 7.48 = gallons
Round: diameter × diameter × average depth × 5.9 = gallons
Oval: length × width × average depth × 5.9 = gallons
Kidney: 0.45 × (width A + width B) × length × average depth × 7.48 = gallons
7.48 is the number of US gallons in one cubic foot of water (many guides round it to 7.5, which overstates every pool by 0.3 %). The round and oval factor 5.9 is 7.48 × π/4, which turns the square of the diameter into the area of the circle. A Roman pool is a rectangle with a half-circle at each end, a Grecian pool a rectangle with its four corners cut at 45°; the calculator uses the exact area for both instead of a rule-of-thumb factor. For an L-shaped pool it adds two rectangles; for a freeform pool enter the surface area from your plan or a satellite measurement. One gallon is 3.785 litres; one cubic metre is 1,000 litres or 264 gallons.
Pools with a drop-off. If the floor does not slope evenly but steps down from the shallow part to a deep well, do not average the depths. Measure the two parts as two pools (the shallow rectangle at its depth, the deep part at its depth) and add the results; the L-shape option does exactly that if you enter each part with its own size and use the average of its depths.
Why the volume matters
Every chemical dose on the label is per 10,000 gallons. A heater is sized from gallons and the temperature rise you want, a pump from gallons and the turnover time, and the fill cost from gallons and your water rate. Get the volume right once, save it above, and the chlorine, salt, alkalinity, heater and pump calculators on this site start from your pool.
Two things make a real pool hold a little less than the formula says: steps, benches and swim-outs displace water, and a sloped floor rarely slopes evenly. If you know your pool was filled from a metered supply, the meter is the better number; use it to correct the result. Overestimating your volume by a third turns a normal chlorine dose into a 133 % dose, so when in doubt, round down.
For scale: a typical inground residential pool holds 15,000 to 25,000 gallons, an above-ground pool 3,000 to 25,000, a swim spa 1,500 to 3,000, and an Olympic pool (50 × 25 m, 2 m deep) about 660,000 gallons.
Frequently asked questions
How many gallons is my pool?
Multiply length × width × average depth × 7.48 for a rectangle (feet), or diameter × diameter × average depth × 5.9 for a round pool. A 16 × 32 ft pool that slopes from 3 to 8 ft holds about 21,000 gallons. The calculator above does this for every shape, exactly.
How many gallons is a 20x40 inground pool?
About 24,000 gallons at an average depth of 4 ft, 30,000 at 5 ft and 33,000 at 5.5 ft (a 3 to 8 ft slope). The formula is 20 × 40 × average depth × 7.48; the exact figure depends on your deep end and on steps and benches.
What size is a 15,000 gallon pool?
A 16 × 32 ft rectangle at an average depth of 4 ft (15,300 gallons), a 24 ft round above-ground pool with a 54 in wall (15,200), or an 18 × 33 ft oval with a 54 in wall (15,800). Many 14 × 28 and 15 × 30 ft inground pools land near 15,000 too.
Is 30,000 gallons a big pool?
Yes. A typical inground residential pool holds 15,000 to 25,000 gallons; 30,000 is a 20 × 40 ft pool with a 5 ft average depth. Above-ground pools hold 3,000 to 25,000. For comparison an Olympic pool holds about 660,000 gallons.
How do I calculate the volume of a pool in litres?
Work out the gallons and multiply by 3.785, or switch the calculator to metres: length × width × average depth in metres gives cubic metres, and one cubic metre is 1,000 litres. A 10 × 5 m pool with 1.5 m of water holds 75,000 litres (19,800 gallons).
How many litres are in a 21 foot round pool?
With a 52 in wall (about 4 ft of water) a 21 ft round pool holds about 10,400 gallons, which is 39,400 litres. With a 48 in wall it holds about 9,100 gallons or 34,500 litres, and with a 54 in wall about 11,700 gallons or 44,300 litres.
What is the average depth of a pool with a shallow and a deep end?
Add the shallow-end depth and the deep-end depth and divide by two. A pool that goes from 3 ft to 8 ft has an average depth of 5.5 ft. This works when the floor slopes evenly; a sudden drop-off makes the real average smaller, so split the pool in two sections.
Why does my pool volume matter?
Every chemical dose on the label is per 10,000 gallons. A volume that is 20 % too high means every chlorine, salt and acid dose is 20 % too high. The heater, the pump and the fill cost are sized from gallons too. Save your pool above and the other calculators use it.