Pool volume calculator: how many gallons is my pool?
Pick the shape, enter the size and the depth (shallow and deep end if the floor slopes) to get your pool’s volume — the number every chemical dose starts from.
Enter your measurements
- Water surface area
- 512 sq ft
- Average depth
- 4.75 ft
- Water in each inch of level
- 319 gal
Rectangle: 32 ft × 16 ft = 512 sq ft
Average depth: (3.5 ft + 6 ft) ÷ 2 = 4.75 ft
512 sq ft × 4.75 ft = 2,432 cu ft × 7.48 = 18,193 gal
- Doses on this site use gallons. Round to the nearest few hundred gallons; your test kit is less precise than that.
Quick answers for common sizes
| Example | Answer |
|---|---|
| How many gallons in a 16x32 inground pool | 18,193 gal |
| How many gallons in a 20x40 inground pool | 34,410 gal |
| How many gallons in an 18x36 inground pool | 27,872 gal |
| How many gallons in a kidney-shaped pool | 13,431 gal |
Gallons at the size above, by deep-end depth
| Deep end | Pool volume (gallons) | Average depth |
|---|---|---|
| 4 ft | 14,363 gal | 3.75 ft |
| 5 ft | 16,278 gal | 4.25 ft |
| 6 ft | 18,193 gal | 4.75 ft |
| 7 ft | 20,108 gal | 5.25 ft |
| 8 ft | 22,023 gal | 5.75 ft |
| 9 ft | 23,938 gal | 6.25 ft |
Every pool chemical label gives its dose per 10,000 gallons (or per 10,000 litres), so the volume is the first number you need — and the one most people guess. Guess 15,000 when the pool holds 20,000 and every chlorine, acid and salt dose is a quarter short. Measure once, write it on the pump house wall, and you’re done.
How the pool volume calculator works
Volume is surface area × average depth. In US units that gives cubic feet; multiply by 7.48 (a US gallon is 231 cubic inches, so a cubic foot holds 7.48052 gallons). In metric, m² × m gives m³, and each m³ is 1,000 litres.
rectangle: length × width × average depth × 7.48 round: 3.1416 × (diameter ÷ 2)² × depth × 7.48 oval (straight sides): [3.1416 × (width ÷ 2)² + (length − width) × width] × depth × 7.48 egg-shaped oval: 0.7854 × length × width × depth × 7.48 kidney: 0.45 × (A + B) × length × depth × 7.48 average depth = (shallow end + deep end) ÷ 2
Measuring: what counts as “depth”
- Water depth, not wall height. Measure from the water surface to the floor. Most pools are filled to the middle of the skimmer opening, a few inches below the coping, so a pool with a 4 ft wall rarely holds 4 ft of water.
- Sloped floors: measure the shallow end at the shallowest point and the deep end at the deepest, and the calculator averages them. That is close for an even slope. A diving pool with a short, steep hopper holds a little less than the simple average suggests.
- Inside dimensions. Measure inside the walls at the water line. Steps, benches and sun shelves take up water, but rarely enough to change a chemical dose — ignore them unless they are large.
- Rounded corners on a rectangular pool cut a few square feet off the area. For dosing, treat it as a rectangle.
Common inground pool sizes
| Size | Shallow / deep | Average depth | Approx. gallons |
|---|---|---|---|
| 12 × 24 ft | 3.5 / 5 ft | 4.25 ft | 9,156 |
| 14 × 28 ft | 3.5 / 6 ft | 4.75 ft | 13,929 |
| 15 × 30 ft | 3.5 / 6 ft | 4.75 ft | 15,990 |
| 16 × 32 ft | 3.5 / 6 ft | 4.75 ft | 18,193 |
| 18 × 36 ft | 3.5 / 8 ft | 5.75 ft | 27,872 |
| 20 × 40 ft | 3.5 / 8 ft | 5.75 ft | 34,410 |
The three sizes people ask about most have their own worked pages, including what a deeper diving end does to the total: how many gallons in a 16x32 inground pool, how many gallons in an 18x36 inground pool and how many gallons in a 20x40 inground pool. For a freeform pool, see how many gallons in a kidney-shaped pool.
Gallons per inch: the number for top-ups and leaks
The result also shows how much water is in each inch (or centimetre) of level. That tells you what a top-up costs, how much the pool lost to evaporation, and how much to drain when you’re lowering stabilizer or salt. A 16 × 32 ft pool holds about 319 gallons per inch, so a 2 in drop is roughly 640 gallons. The pool evaporation calculator works the other way, from weather to inches lost.
Above-ground pools and hot tubs
Above-ground pools have a flat floor, a fixed wall height and a fill line a few inches below the top, which is why manufacturer gallon charts disagree with each other. The above-ground pool calculator works from wall height and fill level. Hot tubs lose a lot of their shell volume to seats and footwells, so use the hot tub gallons calculator or the spec sheet.
What you’ll need
- Hose water flow meterBudget price
Screws onto the hose and counts gallons, so you know exactly how much went in — and your real fill rate.
See options on Amazon (opens in a new tab) - FAS-DPD drop test kit (chlorine, pH, TA, CH, CYA)Mid-range price
A drop-count kit reads free chlorine to 0.5 ppm (or 0.2 ppm), plus pH, alkalinity, calcium and stabilizer. Every dose on this site starts from a test, so this is the one thing worth buying first.
See options on Amazon (opens in a new tab) - Pool test stripsBudget price
Quick daily checks. Fine for spotting a trend; use a drop kit when you’re about to add a big dose or shock.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How do I calculate the gallons in a rectangular pool?
Length × width × average depth × 7.48. A 16 × 32 ft pool going from 3.5 ft to 6 ft deep averages 4.75 ft: 16 × 32 × 4.75 × 7.48052 ≈ 18,193 gallons. See how many gallons in a 16x32 inground pool for other depths.
How do I find the average depth of a pool with a deep end?
Add the shallow-end depth and the deep-end depth and divide by 2. For 3.5 ft and 8 ft, that is 5.75 ft. Measure water depth, from the surface to the floor.
How many litres is my pool?
Switch the calculator to metric, or multiply gallons by 3.785. In metric the formula is simply length × width × average depth in metres × 1,000 litres.
Why does my builder’s gallon figure not match the calculator?
Builders often quote volume to the top of the wall or coping, while you fill a few inches lower, and they may include steps and spa spillovers. A few percent either way makes no practical difference to chemical doses.
How accurate does my pool volume need to be?
Within about 10% is fine. Test kits read chlorine in 0.5 ppm steps and alkalinity in 10 ppm steps, so an exact volume would not make the doses more precise. A guess that is 30% off is the problem.
Related guides
Sources
- NIST Handbook 44, Appendix C — General tables of units of measurement (opens in a new tab) — 1 US gallon = 231 cubic inches, so 1 cubic foot = 7.48052 gallons; 1 gallon = 3.785 litres.
- CDC Healthy Swimming — Home pool and hot tub water treatment and testing (opens in a new tab) — Chemical doses on product labels are given per volume of water, so the volume has to be known first.