Pool Volume Calculator

A pool volume calculator returns a pool's volume in cubic feet and gallons. It multiplies the surface area by the average of the shallow and deep end depths. Surface area comes from the shape: length times width for a rectangle, π times radius squared for a circle, or π times half the length times half the width for an oval.

Last reviewed September 2026Method & sources Report an error

Not to scale.

Surface Area

800 sq ft

Breakdown
Surface Area	800 sq ft
Volume	4,400 cu ft
Volume	32,914 gal

How to Calculate Pool Volume

Volume is Surface Area × Average Depth. Surface area depends on shape: Length × Width for a rectangular pool, π × radius² for circular (using the diameter you enter, halved). For an oval, the formula π × (length ÷ 2) × (width ÷ 2) treats the pool as an ellipse. Average depth is simply the shallow and deep end depths averaged. This is a reasonable approximation for a pool with a sloped bottom transitioning between the two, though it is not exact for pools with a large flat deep-end shelf or an unusual bottom profile. The volume in cubic feet converts to gallons by multiplying by 7.48052, the exact number of US gallons in one cubic foot.

Example: Rectangular 20 ft × 40 ft pool, 3 ft shallow end, 8 ft deep end

A rectangular 20 ft × 40 ft pool, 3 ft shallow end, 8 ft deep end: 1. Average depth: (3 + 8) ÷ 2 = 5.5 ft 2. Surface area: 20 × 40 = 800 sq ft 3. Volume: 800 × 5.5 = 4,400 cubic feet 4. Gallons: 4,400 × 7.48052 ≈ 32,914 gallons. A circular pool with the same 20 ft diameter and the same average depth would have far less volume: π × 10² × 5.5 ≈ 1,728 cubic feet (about 12,927 gallons). A circle's area is much smaller than a rectangle built from the same outer dimension.

Pool Volume: Compare Scenarios

Scenario	Surface Area	Volume	Volume
Small (12×24 ft plunge pool)	288 sq ft	1,584 cu ft	11,849 gal
Medium (20×40 ft pool)	800 sq ft	4,400 cu ft	32,914 gal
Large (30×50 ft pool)	1,500 sq ft	8,250 cu ft	61,714 gal

What Is Pool Volume?

A pool volume calculator converts your pool's dimensions into its total water volume, in both cubic feet and gallons. Pool volume is the basis for nearly every chemical dosing calculation (chlorine, pH adjusters, algaecide, and more). Dosing instructions are almost always given per gallon or per thousand gallons of pool water.

Pool Volume: Pros and Cons

Pros

Covers the three most common residential pool shapes (rectangular, circular, oval) in one calculator
Uses shallow and deep end depths separately, rather than requiring you to already know an average depth figure
Gives both cubic feet and gallons, since different chemical products and calculations use different units

Cons

The average-depth approximation assumes a fairly linear slope between the shallow and deep ends. A pool with a large flat deep-end shelf, a shallow tanning ledge, or an unusual bottom profile will have a somewhat different actual volume
An oval pool is approximated as a true ellipse. A stadium-shaped (rounded rectangle) pool, common in some designs, has a different area formula and will be slightly overestimated or underestimated by the oval option
Doesn't account for water displaced by pool steps, benches, or other built-in features, which reduce actual water volume slightly below this calculator's geometric estimate

Pool Volume: What a Pro Checks

Use your pool's actual average depth, not a guess. Average the shallow and deep end depths, since nearly every chemical dosing instruction (chlorine, shock, pH adjusters, algaecide) is based on total volume, usually per gallon or per 10,000 gallons.
Recheck the volume figure if your pool has a large flat deep-end shelf, a tanning ledge, or an unusual bottom profile. The shallow/deep average assumes a fairly linear slope, and a flat shelf holds more water than that average suggests.

Frequently Asked Questions

How many gallons is my pool?

Multiply your pool's surface area by its average depth to get cubic feet, then multiply by 7.48052 to convert to gallons. A rectangular 20 ft × 40 ft pool averaging 5.5 ft deep holds about 32,914 gallons.

How do I calculate average depth?

For a pool with a simple slope from a shallow end to a deep end, average the two depths: (shallow + deep) ÷ 2. This is an approximation. A pool with a large flat area at the deep-end depth (rather than a continuous slope) will hold somewhat more water than this average suggests.

Why does pool volume matter?

Almost every pool chemical (chlorine, shock, pH adjusters, algaecide) is dosed based on total pool volume, usually per gallon or per 10,000 gallons. Using the wrong volume figure means over- or under-dosing chemicals, which can lead to water balance and safety issues.

How is an oval pool's area calculated?

This calculator treats an oval pool as a true ellipse: π × (length ÷ 2) × (width ÷ 2). Some pools marketed as "oval" are actually a stadium shape (a rectangle with semicircular ends), which has a slightly different area formula. If your pool has straight sides with rounded ends rather than a smooth continuous curve, this calculator's oval option will be an approximation.

Does a circular pool hold less water than a rectangular one of the same width?

Yes, significantly less. A circle's area is about 79% of the area of a square with the same width (π/4 ≈ 0.785), and even less compared to a rectangle that's longer than it is wide. The worked example above shows a 20 ft circular pool holding well under half the volume of a 20x40 ft rectangular pool at the same average depth.

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