Pool volume calculator: how many gallons is your pool?

Formulas checked 11/9/2026

Multiply length by width by average depth, then by 7.5 for a rectangular pool or 5.9 for an oval one. For a round pool, multiply the diameter by itself, then by the average depth and 5.9. Average depth is the shallow end plus the deep end, divided by two. Measure in feet; the answer is in US gallons.

Checked on every build: 26 tests of the sums this calculator runs, including 10 amounts printed in published charts, labels and manuals (ours must match them, or land under them where we start low on purpose).

Read before you add anything

Never add acid and chlorine at the same time, and never mix them, even in a bucket or feeder. Mixing chlorine products with acid can create toxic gas. Add one, let the pump run, retest, then add the other.
Always add the chemical to water, never water to the chemical.
Add one chemical at a time. Never mix chemicals together, and use a separate clean scoop for each.
Add chemicals only when nobody is in the pool.
Wear the protective gear your product label asks for, such as goggles and gloves.
Handle chemicals in a well-ventilated area.
Add acid with the pump running, into the deep end, away from the skimmer and away from any floater or feeder that holds chlorine tablets.
Never add shock (cal-hypo or any other chlorine product) through the skimmer, or through any floater or feeder that holds or has held tablets, and never put different chlorine products in the same feeder.
Only pre-dissolve a chemical in a bucket if its label tells you to.
Store chemicals in a secure place away from children and pets, and never store liquid chemicals above dry chemicals.
Read the product label before each use. If the label differs from this estimate, follow the label.
These amounts are estimates. Add in stages and retest before adding more.
This tool cannot tell you the water is safe to swim in. Follow your product label, and if in doubt ask a pool professional.

Where each line comes from

CDC, Using Pool Chemicals Safely Official: “Never mix / Chlorine products with acid; this could create toxic gases” Source page (opens in a new browser tab)
12.5% liquid chlorine label, EPA-accepted Other source: “Mixing this product with chemicals (e.g. ammonia, acids, detergents, etc.) or organic matter (e.g. urine, feces, etc.)” ... “will release chlorine gas which is irritating to eyes, lungs and mucous membranes.” Source page (opens in a new browser tab)
CDC Official: “add pool chemical to water; NEVER add water to pool chemical” and “violent (potentially explosive) reaction can occur” Source page (opens in a new browser tab)
Virginia Department of Health Official: “Add chemicals to water - not water to chemicals.” Source page (opens in a new browser tab)
Indiana Department of Health Official: “Add acids to water, NEVER water to acid. Remember AAA (Always Add Acid).” Source page (opens in a new browser tab)
CDC Model Aquatic Health Code 2024, 5.9.3.4.2.3.1 Official: “Two or more chemicals shall never be mixed in the same dilution water.” Source page (opens in a new browser tab)
Indiana Official: “Never mix any chemicals together.” Source page (opens in a new browser tab)
Virginia Official: “Designate tools per chemical - Do not use the same scoop for different chemicals.” Source page (opens in a new browser tab)
MAHC 5.9.3.4.1.2 Official: “Chemicals added manually directly into the AQUATIC VENUE shall only be introduced in the absence of BATHERS.” Source page (opens in a new browser tab)
Virginia Official: “NEVER add pool chemicals when the pool is in use, and only add them poolside as directed by the product label.” Source page (opens in a new browser tab)
CDC, Using Pool Chemicals Safely Official: “Dress for safety by wearing appropriate safety equipment (for example, safety goggles, gloves, and mask)” Source page (opens in a new browser tab)
12.5% liquid chlorine label, EPA-accepted Other source: “Wear safety glasses or goggles and rubber gloves when handling this product.” Source page (opens in a new browser tab)
Alliance Trading pH Down (dry acid) label Other source: “Wear goggles or safety glasses and rubber gloves when handling this product.” Source page (opens in a new browser tab)
CDC, Using Pool Chemicals Safely Official: “Handle in a well-ventilated area” Source page (opens in a new browser tab)
Leslie's muriatic acid Other source: “With the pump running, pour the solution into the deep end of your pool, or away from the skimmer or any fixtures.” Source page (opens in a new browser tab)
Alliance Trading pH Down label Other source: “To add this product, broadcast into the deep end of the pool when not in use.” and “Do not add near metal fittings nor allow pH to drop below 7.2.” Source page (opens in a new browser tab)
CDC Official: “Never mix / Chlorine products with acid; this could create toxic gases” Source page (opens in a new browser tab)
UConn Health, Connecticut Poison Control Center, "Splish Splash Safety" Other source: “Keep acids away from other chemicals.” Source page (opens in a new browser tab)
Alliance Chemical 12.5% sodium hypochlorite safety data sheet Other source: “Never mix with acids, ammonia or other cleaning products: this releases toxic chlorine or chloramine gas.” Source page (opens in a new browser tab)
HTH Pool Care Shock, calcium hypochlorite 52% Other source: “Do not use this product in a floater or feeder.” Source page (opens in a new browser tab)
HTH 3" Chlorine Tabs Advanced Other source: “Do not use this product in floaters or feeders that have been used with other chlorinating products.” and “Do not use with any other tablets or sticks in the same skimmer, floater, or feeder.” Source page (opens in a new browser tab)
BioGuard cal-hypo label, EPA-accepted Other source: “Do not add this product to any dispensing device containing remnants of any other product.” Source page (opens in a new browser tab)
CDC Official, under “Never mix”: “Different pool chemicals (for example, different types of chlorine products) with each other or with any other substance” Source page (opens in a new browser tab)
CDC Official: “Only pre-dissolve pool chemicals when directed by product label” Source page (opens in a new browser tab)
Virginia Official: “Store chemicals in secure location away from children and pets.” Source page (opens in a new browser tab)
Virginia Official: “Never store liquid chemicals above dry chemicals.” Source page (opens in a new browser tab)
CDC Official: “Read chemical product label before each use” Source page (opens in a new browser tab)
Yakima County chart Official: “NOTE: This chart gives approximate amounts of each chemical listed. Always read the labels for exact” / “amounts needed for your chemical adjustments.” Source page (opens in a new browser tab)
Licking County Official: “Always follow instructions on the manufactures label for exact dosage amounts and handling.” Source page (opens in a new browser tab)
Multnomah County Official: “It is always better to add part of the required amount of chemical over several occasions” ... “than all at once (EXCEPTION: breakpoint chlorination).” Source page (opens in a new browser tab)
Indiana Official: “Add large amounts gradually in thirds over a 2-hour period.” Source page (opens in a new browser tab)
Our own rule for every result: we point you to your label and the official guidance instead.

The formula for each shape

Measurements in feet; answers in US gallons
Shape	Formula	Source
Rectangle	Length x width x average depth x 7.5	City of Oregon City (Oregon) Official: Take the length time’s width, times the average depth, times 7.5.
Round	Diameter x diameter x average depth x 5.9	City of Oregon City (Oregon) Official: Take the Diameter times Diameter, times the average depth, times 5.9.
Oval	Length x width x average depth x 5.9	City of Oregon City (Oregon) Official: Take the length time’s width, times the average depth, times 5.9.
Kidney	0.45 x (widest width at one end + widest width at the other) x length x average depth x 7.5	A water utility's pool calculator page that names no publisher Other source; we found no official kidney formula: 0.45 x (A+B) x length x average depth x 7.5 = volume (in gallons).
Irregular (free-form)	Longest length x widest width x average depth x 5.9	Leslie's, a pool retailer Other source: Longest Length × Widest Width × Average Depth × 5.9 = approximate volume (gallons).

Average depth: the City of Akron (Ohio) water works it out like this: 2' + 10' = 12'; 12'/2 = 6' Average Depth.

Sloping sides: Pentair's guide says Sloping sides: Multiply total gallons by 0.85. Tick the box and the calculator does that.

Where sources give different multipliers, the calculator uses the smaller one, so chemical amounts err low. For free-form pools, City of Akron (Ohio) water uses 7.5 instead of 5.9. For ovals, Pentair uses 6.7 instead of 5.9: an oval with straight sides can hold more than the smaller formula says.

For example, say a rectangular pool is 32 ft long and 16 ft wide, 3.5 ft deep at the shallow end and 6 ft at the deep end. The average depth is 4.75 ft, so it holds about 18,240 US gallons (69,046 liters).

Why the size matters

Every chemical amount on this site is worked out per 10,000 US gallons and scaled to your pool, so a wrong size gives a wrong amount. Real pools with sloped walls, steps or benches usually hold less than the shape formula. US gallons are not UK gallons: UK gallons x 1.2 = US gallons. If you know your size in liters, the calculators take liters as well.

How many gallons is an Olympic pool?

World Aquatics' rules give a length of 50 m and a width of 25 m for Olympic pools, and say FR 3.3 - Depth: 2 Metres (minimum); 3 metres recommended, when using the pool for multi disciplines. At that minimum depth, it holds about 660,430 US gallons.

Questions people ask

How many gallons is my pool?

For a rectangular pool: length x width x average depth x 7.5, all in feet. For round: diameter x diameter x average depth x 5.9. The calculator does every shape and gives liters too.

How do I work out the average depth?

Add the shallow end depth to the deep end depth and divide by two. If the pool is the same depth all over, use that depth.

How many gallons are in an Olympic swimming pool?

About 660,430 US gallons at the minimum depth in World Aquatics' rules.

Do I need the size in US gallons?

Yes, or in liters. The dose charts are per 10,000 US gallons. A UK gallon is bigger: UK gallons x 1.2 = US gallons.

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The charts behind this page

Show all 10 figures and where each one comes from

Each figure this page and its calculator use. Open one for the source's own words, the other sources we checked it against, and the checks it has been through.

Average depth = (shallow end + deep end) / 2: shallow end plus deep end, halved Official
City of Akron (Ohio) water: How to calculate the gallons in a swimming pool Official says: 2' + 10' = 12'; 12'/2 = 6' Average Depth Source page (opens in a new browser tab)
Also checked: a water utility's pool calculator page (no publisher named) Other source says: Average depth = ( 3 + 9 ) / 2 = 6 feet. Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
Rectangle: length x width x average depth x 7.5 = US gallons: 7.5 US gal per cubic ft (multiplier) Official
City of Oregon City (Oregon): Swimming Pool Water Estimator Official says: Take the length time’s width, times the average depth, times 7.5. Source page (opens in a new browser tab)
Also checked: City of Akron (Ohio) water: How to calculate the gallons in a swimming pool Official says: Length * Width * Average Depth * Multiplier = Gallons Source page (opens in a new browser tab)
Also checked: Pentair IntelliChlor IC15/20/40/60 Installation and User's Guide, P/N 520589 Rev R Other source says: Rectangular Pools: Length x width x average depth x 7.5 Source page (opens in a new browser tab)
Also checked: a water utility's pool calculator page (no publisher named) Other source says: 25.75 ft x 10 ft x 6 ft x 7.5 = 11,587.5 gallons Source page (opens in a new browser tab)
Also checked: NIST Special Publication 811, Appendix B.8 conversion factors Official says: cubic foot (ft3) to cubic meter (m3) 2.831 685 E-02; gallon (U.S.) (gal) to cubic meter (m3) 3.785 412 E-03 Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure. Looked up again on 11/10/2026 by a checker who couldn't see our figure: it came back with the same figure.
Round: diameter x diameter x average depth x 5.9 = US gallons: 5.9 multiplier Official
City of Oregon City (Oregon): Swimming Pool Water Estimator Official says: Take the Diameter times Diameter, times the average depth, times 5.9. Source page (opens in a new browser tab)
Also checked: City of Akron (Ohio) water: How to calculate the gallons in a swimming pool Official says: Length * Width * Average Depth * Multiplier = Gallons Source page (opens in a new browser tab)
Also checked: Leslie's: Calculating pool volume Other source says: 3.14 × Radius × Radius × Average Depth × 7.5 = volume (gallons) Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure. Looked up again on 11/10/2026 by a checker who couldn't see our figure: it came back with the same figure.
Oval: length x width x average depth x 5.9 = US gallons: 5.9 multiplier Official
City of Oregon City (Oregon): Swimming Pool Water Estimator Official says: Take the length time’s width, times the average depth, times 5.9. Source page (opens in a new browser tab)
Also checked: City of Akron (Ohio) water: How to calculate the gallons in a swimming pool Official says: Length * Width * Average Depth * Multiplier = Gallons Source page (opens in a new browser tab)
Also checked: Leslie's: Calculating pool volume Other source says: 3.14 × Length × Width × 0.25 × Average Depth × 7.5 = approximate volume (gallons) Source page (opens in a new browser tab)
Also checked: Pentair IntelliChlor IC15/20/40/60 Installation and User's Guide, P/N 520589 Rev R Other source says: Oval Pools: Length x width x average depth x 6.7 Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
Kidney: 0.45 x (A + B) x length x average depth x 7.5 = US gallons (A, B = widths at the two widest points): 0.45 shape factor Other source
a water utility's pool calculator page (no publisher named) Other source says: 0.45 x (A+B) x length x average depth x 7.5 = volume (in gallons) Source page (opens in a new browser tab)
Also checked: Leslie's: Calculating pool volume Other source says: (A + B) × Length × 0.45 × Average Depth × 7.5 = approximate volume (gallons) Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
Irregular / free-form: longest length x widest width x average depth x 5.9 = US gallons: 5.9 multiplier Other source
Leslie's: Calculating pool volume Other source says: Longest Length × Widest Width × Average Depth × 5.9 = approximate volume (gallons) Source page (opens in a new browser tab)
Also checked: City of Akron (Ohio) water: How to calculate the gallons in a swimming pool Official says: Length * Width * Average Depth * Multiplier = Gallons Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
Sloping sides: multiply total US gallons by 0.85: 0.85 multiplier (optional) Other source
Pentair IntelliChlor IC15/20/40/60 Installation and User's Guide, P/N 520589 Rev R Other source says: Sloping sides: Multiply total gallons by 0.85 Source page (opens in a new browser tab)
Checked against the source on 11/9/2026.
US gallon to liters: 3.785412 L per US gal Official
NIST Special Publication 811, Appendix B.8 conversion factors Official says: gallon (U.S.) (gal) | liter (L) | 3.785 412 | E+00 Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
Foot to meters (exact): 0.3048 m per ft Official
NIST Special Publication 811, Appendix B.8 conversion factors Official says: foot (ft) | meter (m) | 3.048 | E-01 Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
Olympic pool (50 m x 25 m x 2 m minimum depth) volume: 660,430 US gallons (at the 2 m minimum depth) Other source (worked out)
Worked out: 50 × 25 × 2 = 2,500 m³ = 2,500,000 L ÷ 3.785412 = 660,430 US gal (at 3 m: 990,645 US gal)
FINA / World Aquatics: FR 3 Swimming Pools for Olympic Games and World Championships Other source says: FR 3.3 - Depth: 2 Metres (minimum); 3 metres recommended, when using the pool for multi disciplines Source page (opens in a new browser tab)
Also checked: FINA / World Aquatics: FR 3 Swimming Pools for Olympic Games and World Championships Other source says: FR 3 - Length: 50.0m between the Automatic Officiating Equipment touch panels Source page (opens in a new browser tab)
Also checked: FINA / World Aquatics: FR 3 Swimming Pools for Olympic Games and World Championships Other source says: OLYMPIC GAMES: - Permanent Swimming Pools 25.00 meters Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's own words quoted here.