How many gallons is my pool? Sizes and charts
It is the first question every pool owner asks. Here is a fast way to answer it — plus a chart for the most common pool sizes.
“How many gallons is my pool?” has a simple answer: measure the water’s footprint and its average depth, then convert to gallons with 7.48 gallons per cubic foot. You do not need the manufacturer’s label or a receipt — a tape measure is enough, and the result is the number you will reuse for salt, chlorine and heating.
The 30-second method
For the two most common shapes:
- Rectangular: length × width × average depth × 7.5
- Round / above-ground: diameter × diameter × average depth × 5.9
All measurements are in feet, and average depth is (shallow + deep) ÷ 2. The 7.5 and 5.9 are the standard shape multipliers; the round formula uses diameter × diameter (not the radius) because the 5.9 already includes the π ÷ 4 area factor for a circle.
Worked examples
16 × 32 ft rectangle, average depth 5 ft: 16 × 32 × 5 × 7.5 = ≈ 19,200 gallons (the exact 7.48 constant gives 19,149).
24 ft round, average depth 4 ft: 24 × 24 × 4 × 5.9 = ≈ 13,600 gallons.
18 × 33 ft oval, average depth 4 ft: using π × 9 × 16.5 × 4 × 7.48 gives ≈ 13,957 gallons.
Reference chart: gallons by common pool size
Approximate US gallons for popular sizes. Rectangular figures assume an average depth of 4.5 ft; round figures assume 4 ft. Your pool may differ — use these as a sanity check, not a substitute for measuring.
Rectangular pools (avg depth 4.5 ft)
| Size (ft) | Gallons |
|---|---|
| 12 × 24 | ≈ 9,700 |
| 14 × 28 | ≈ 13,200 |
| 16 × 32 | ≈ 17,200 |
| 18 × 36 | ≈ 21,800 |
| 20 × 40 | ≈ 26,900 |
Round / above-ground pools (avg depth 4 ft)
| Diameter (ft) | Gallons |
|---|---|
| 15 | ≈ 5,300 |
| 18 | ≈ 7,600 |
| 21 | ≈ 10,400 |
| 24 | ≈ 13,600 |
| 27 | ≈ 17,200 |
The full, exact version of these charts lives on the pool gallons table.
Why guessing is risky
Rounding “about 20,000 gallons” for a pool that actually holds 15,000 means every chemical dose is 33% too strong. Over-chlorinating or over-salting is wasteful at best and, with acid or shock, unsafe. Because the volume feeds every other calculation on this site, a few minutes with a tape measure is the highest-value thing you can do for accurate pool care.
If your pool is an irregular freeform shape, break it into simpler pieces — a rectangle plus a half-circle, say — find each piece’s gallons, and add them up. It is more reliable than trying to fit one formula to a complex curve.
Above-ground vs in-ground pools
The shape math is the same, but two practical differences change the number you plug in. Above-ground pools are almost always a constant depth, so the “average” is simply the water depth — and because they are filled below the top rail, that depth is often 6–12 inches less than the pool’s stated wall height. Round and oval framed pools dominate this category, so the 5.9 multiplier applies. In-ground pools usually slope from a shallow end to a deep-end hopper, so you must average the depths, and freeform or L-shaped designs may need to be split into simpler pieces and summed.
Gallons, liters and rounding
US pool care runs on gallons and pounds, but if you ever need metric, multiply gallons by 3.785 to get liters. For chemistry it rarely matters which unit you started in, because doses are expressed in ppm — parts per million by weight — which is unit-independent. What does matter is rounding to a sensible working volume. Once you have a figure like 19,149 gallons, plan salt and chemicals around ~19,000; the extra precision is smaller than the error in a tape-measured pool, and dosing to about three-quarters of the calculated amount and re-testing is safer than chasing an exact number.
When to re-measure
Your gallons figure is stable — geometry does not change — so you measure once and reuse it. The exceptions are real physical changes: raising or lowering the water line for the season, a renovation that alters depth, or adding an attached spa or ledge. In those cases, re-measure the affected part and update your working volume, since every dose downstream depends on it.
The bottom line
Your pool’s gallons is the one measurement worth getting right, because every chemical dose and every heating time is built on it. Measure length, width and average depth at the water line, multiply by 7.5 for a rectangle or 5.9 for a round or oval pool, and you have a figure accurate enough for all your salt, chlorine and heater math. Cross-check it against the chart for your size; if the two disagree sharply, re-measure rather than split the difference. Then write the number down and reuse it all season — it only changes if you physically alter the pool or its water line. Five careful minutes with a tape measure now means you never again have to guess at how much salt, chlorine or shock your pool actually needs.
For an exact figure with the math shown, run your numbers through the pool volume calculator or the shape-specific rectangular and round tools.