Pool Volume Calculator
Gallons and liters for any pool shape — with the math behind every number, sourced from NIST and CRC, not pool-store charts.
Why your pool's volume matters
A 16×32 ft pool holds about 22,000 gallons. That's 92 tons of water — heavier than a fully loaded Boeing 737.
Get that number wrong by 20%, and every chlorine dose, every bag of salt, and every heating estimate you make this summer is wrong by 20% too.
Here's the deal: this calculator gives you your pool's exact volume in gallons and liters for any shape — rectangle, round, oval, kidney, L-shape, even a diving pool with a deep-end hopper. You'll see every step of the math, not just the answer. Two minutes, one number, and everything else on this site gets easier.
The calculator
Pick your shape and the diagram updates to show exactly which dimensions to measure. Then type the numbers, hit calculate. Defaults match the 16×32 example from below — change them to match your pool, or run the defaults first to see what the result panel looks like.
Calculate your pool's volume
Pick a shape, fill the boxes, hit calculate. Every step shown below.
The 5.9 vs 6.7 multiplier fight, finally explained
Here's the part most charts get silently wrong. A true ellipse 15×30 ft has 353 ft² of surface. But your above-ground "oval" isn't an ellipse — it's a rectangle with two half-circle ends, a shape geometers call a stadium.
That stadium covers 402 ft² — about 14% more than the ellipse. That gap is exactly why some charts multiply by 5.9 and others by 6.7. They're describing two different shapes and never telling you which.
Worked check:15×30 stadium = 15·(30−15) + (π/4)·15² = 225 + 176.7 = 401.7 ft². Our calculator runs both — pick the tab that matches the shape of your actual pool.
Six shapes, six formulas
The calculator handles all six (plus diving pools via the segment method). Here is the geometry beneath each — useful when you're cross-checking by hand or sanity-testing a chart.
Worked examples for common pool sizes
Eight pools, eight precomputed answers. Plug your own numbers into the calculator above — these are the sanity checks.
Example 1
Swimming pool volume calculator: 16×32 inground example
16 × 32 ft, shallow 3.5 ft, deep 8 ft, constant slope. Average depth = 5.75 ft.
22,023 gal
Area 512 ft²; 2,944 ft³; 83,365 L; 91.8 US tons (183,672 lb).
The most common inground size in the US. The water alone outweighs a loaded Boeing 737-800 (max takeoff ≈ 174,200 lb) — your deck or slab is doing serious structural work.
Example 2
Pool capacity calculator: 20×40 with a 5.5 ft average depth
20 × 40 ft, constant slope, average depth 5.5 ft.
32,914 gal
Area 800 ft²; 4,400 ft³; 124,594 L; 137 US tons.
Capacity scales linearly. This pool is 49% bigger than the 16×32 above, so it needs exactly 49% more of every chemical, every dose.
Example 3
Oval pool volume: the 15×30 above-ground (stadium shape)
15 × 30 ft stadium (typical AGP oval), water depth 4.0 ft (48 in).
12,020 gal
Area 401.7 ft²; 1,606.9 ft³. The true-ellipse math for the same dimensions gives 10,575 gal — about 12% lower.
This is the 5.9-vs-6.7 multiplier fight resolved. Above-ground ovals are stadiums, not ellipses — use 12,020.
Example 4
Kidney shaped pool volume calculator example
18 × 36 ft bounding box, 0.85 freeform factor, average depth 4.5 ft.
≈ 18,541 gal
Area ≈ 550.8 ft²; 2,478.6 ft³. Honest error bars: ±10% → 16,700–20,400 gal.
Freeform = estimate. If dosing precision matters, refine with the segment method or count grid squares on a scaled sketch.
Example 5
L shaped pool volume calculator example
Section A 20×10 ft @ AD 5 ft = 1,000 ft³. Section B 10×10 ft @ AD 4 ft = 400 ft³.
10,473 gal
Total 1,400 ft³; 39,644 L.
Any weird footprint is just rectangles in a trench coat — split, compute, add.
Example 6
Pool volume calculator in litres: 8×4 m metric example
8 × 4 m, depths 1.2 / 2.0 m → average depth 1.6 m.
51,200 L
Area 32 m²; 51.2 m³; 13,526 US gal.
Metric is cleaner — 1 m³ is exactly 1,000 L, no 7.48 to remember. For EU and AU readers.
Example 7
Small pool / Intex pool volume: 12 ft round example
12 ft diameter, water depth 26 in (≈ 2.17 ft) in a 30-in-wall ring pool. Cylinder math (π/4 × D²) × depth.
1,833 gal
Area 113.1 ft²; 245 ft³. Cylinder geometry; manufacturer specs typically come in lower because inflatable top rings taper the column.
Small pools are unforgiving — a 10% volume error is a 10% chlorine error in a tub-sized body of water. Use the manufacturer figure for dosing if you have it.
Example 8
Diving pool with deep-end hopper (segment method)
18 × 36 ft split into three: shallow 12 ft @ AD 3.5 ft (756 ft³) + slope 12 ft @ AD 5.75 ft (1,242 ft³) + hopper 12 ft @ AD 6.5 ft (1,404 ft³).
25,449 gal
Total 3,402 ft³.
The naive (shallow + deep)/2 shortcut gives 27,872 gal here — a 9.5% overdose on every chemical, forever. (Naive: 18 × 36 × 5.75 = 3,726 ft³ = 27,872 gal vs segment 25,449 gal; Δ 2,423 gal.)
Eight pools at a glance
Every bar below is one of the worked examples above. The chart makes two patterns visible: the diving 18×36 nearly catches the 16×32 despite a smaller footprint (deep-end physics), and the 15×30 oval AGP holds noticeably less than its 18×36 kidney cousin (shape matters more than people assume).
Reference tables
Two tables you can cite directly. Both are released under CC BY 4.0 — reuse them with a link back.
T1 · Shape multipliers and when to use them
AD = average depth. Multipliers fold the exact 7.48052 gal/ft³ and the relevant shape constant into one number.
| Shape | Area formula | Volume (US gal) | When to use | Source |
|---|---|---|---|---|
| Rectangle | L × W | L × W × AD × 7.48 | Standard inground rectangles | F2 (NIST) |
| Round | (π/4) × D² | D² × AD × 5.87 | True round shapes — ring AGPs, tanks | F2, F7 (geometry + NIST) |
| Oval (stadium) | W·(L−W) + (π/4)·W² | (stadium area) × AD × 7.48 | Typical above-ground oval — most AGPs labeled "oval" | F8 (geometry) |
| True ellipse | (π/4) × L × W | L × W × AD × 5.87 | Genuinely elliptical pools (rare custom builds) | F9 (geometry) |
| Kidney / freeform | 0.85 × L × W | L × W × AD × 6.36 | Bounding-box estimate, ±10%; refine if dosing matters | F10 (industry convention) |
| L-shape | A₁ + A₂ | Sum of per-section volumes | Any L footprint; split into rectangles | §4.2 (geometry) |
T2 · Quick volumes for common inground sizes (US gal)
All values use the exact 7.48052 gal/ft³ conversion and a constant-slope average depth. Read across to your average depth.
| Footprint (ft) | AD 4.5 ft | AD 5.5 ft | AD 6.5 ft |
|---|---|---|---|
| 12 × 24 | 9,695 | 11,849 | 14,004 |
| 14 × 28 | 13,196 | 16,128 | 19,060 |
| 15 × 30 | 15,148 | 18,514 | 21,881 |
| 16 × 32 | 17,235 | 21,065 | 24,895 |
| 18 × 36 | 21,813 | 26,661 | 31,508 |
| 20 × 40 | 26,930 | 32,914 | 38,899 |
A 16×32 at 5.5 ft average depth (21,065 gal) sits mid-range among common inground sizes — handy anchor when sanity-checking the calculator above.
Methodology & sources
Conversions on this page come from NIST Handbook 44 and NIST SP 811 — the US legal definitions of the gallon (exactly 231 cubic inches) and its SI equivalents. That's why our 7.48052 is exact, instead of the rounded 7.5 you'll see on chemical labels and pool-store charts.
Water density comes from the CRC Handbook of Chemistry and Physics, quoted at 60 °F with its temperature dependence acknowledged. Shape multipliers are derived from plane geometry directly on this page — nothing imported on faith — and the worked check for the stadium oval in the section above makes the derivation auditable.
Where the industry uses estimating conventions — the 0.85 kidney factor, the typical 90% above-ground fill, the rounded 5.9 multiplier — we label them as conventions with their error bars rather than presenting them as facts. CDC's Model Aquatic Health Code makes volume the denominator of every chemical dose, which is why a 5% volume error becomes a 5% dosing error, forever.
Sources used on this page
- NIST Handbook 44— US legal metrology reference. We took the exact definition of the US liquid gallon as 231 cubic inches, which makes our 7.48052 gal/ft³ conversion exact rather than rounded.
- NIST SP 811— SI unit conversions. We took the exact equivalence 1 US gal = 3.785411784 L for every imperial-to-metric output.
- CRC Handbook of Chemistry and Physics— standard reference for physical constants. We use it for water density at typical pool temperatures and to acknowledge the small (≈0.5%) shift between cold and warm water.
- PHTA / APSP estimating conventions— industry-published shape factors. We use the 0.85 kidney/freeform factor and AGP fill conventions explicitly as conventions, with their stated error bars (~±10% for kidney).
- CDC Model Aquatic Health Code— the public-health basis for the "volume drives dosing" principle. We cite it as the reason volume accuracy is load-bearing for every chemistry page on this site.
Reference tables T1 and T2 above are released under CC BY 4.0. Reuse them anywhere — just attribute PoolSolver and link back.
Frequently asked questions
How do I calculate pool volume?
Multiply the pool's surface area by its average depth, then multiply by 7.48 to get US gallons. The 7.48 comes from the legal definition: 1 gallon = 231 cubic inches (NIST Handbook 44), and there are 1,728 cubic inches in a cubic foot.
How many gallons is the average pool?
A typical residential inground pool holds 18,000 to 30,000 gallons. A 16×32 ft inground at an average 5.5 ft depth is 21,065 gallons — see the quick-volume table above for five more common sizes.
Is the average-depth method accurate?
It's exact for a pool with a constant-slope floor. It overestimates for a diving pool with a deep-end hopper, because the hopper's inward-sloping walls aren't accounted for — use the segment method (the Diving tab in our calculator) instead.
Should I use 7.5 or 7.48 gallons per cubic foot?
Use 7.48052. Rounded 7.5 inflates your volume by about 0.26% — seems small until you scale it across every chemical addition and every season.
Do I measure water depth or wall height?
Water depth. Above-ground pools sit below the top rail, typically with 2 to 6 inches of freeboard. Using wall height instead can leave you 10–15% off — a chronic chemical overdose baked into every refill.
How do I convert gallons to liters?
Multiply by 3.78541. That's exact, by international agreement: 1 US gallon = 3.785411784 liters per NIST SP 811.
Why does pool volume matter for chemicals?
All chemical dosing scales linearly with volume — half the gallons means half the dose. Get the volume right and the chemistry, salt, and heater sizing on the rest of this site all become trustworthy.
How much does pool water weigh?
About 8.34 pounds per gallon at typical pool temperatures. For a 16×32 pool: 22,023 gal × 8.34 ≈ 183,672 lb, or 91.8 US tons — heavier than a fully loaded Boeing 737.
Related calculators
Next in Pool Chemistry: Pool Salt Calculator.
More in Pool Chemistry: Pool Chlorine Calculator.
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All Pool Chemistry calculators: browse the hub.