Infinity Pool Volume Calculator

How to Use This Infinity Pool Volume Calculator

What Is Infinity Pool Volume?

Infinity pool volume is the total amount of water the entire overflow system holds — not just the water visible in the main swimming basin. It is measured in US gallons, litres, or cubic metres and determines every chemical dose, every heater calculation, and every pump capacity decision.

Most infinity pools include a main basin plus a separate balance tank or surge tank that catches water flowing over the vanishing edge. Because this tank holds active, circulating water, total system volume can exceed the visible pool volume by 1,500–3,000 gallons (5,678–11,356 L) on a typical residential design. Among all the shapes covered by our pool volume calculators, the infinity pool is unique because its total water includes a hidden hydraulic component.

Main Basin Volume vs Balance Tank Volume

The main basin is the swimming area — the pool itself. Its volume depends on internal length, width, and the average of the shallow and deep end depths.

The balance tank (also called a surge tank, catch basin, or overflow trough) sits below or behind the infinity edge. It collects water that flows over the vanishing edge, holds it temporarily, and feeds it back into the main basin through the circulation pump. Its own volume is determined by its internal length, width, and operating water depth.

Some infinity pool systems use a narrow trough along the overflow edge that drains into a larger underground surge tank. Others combine the trough and tank into a single catch basin. The exact hydraulic layout depends on the system design.

For chemical dosing and equipment sizing, total system volume — main basin plus balance tank — is the figure that matters. Treating only the visible basin leaves the circulating water under-dosed because the balance tank water moves through the same treatment loop.

How to Calculate Infinity Pool Volume

The main basin of most infinity pools follows a rectangular plan, so the base formula is the same one used for a rectangular pool. The difference is that an infinity pool adds a balance tank to reach the true total system volume. For a full breakdown of conversion factors, see the pool volume formula reference.

The Infinity Pool Volume Formula

Main Basin Volume (ft³) = Length × Width × Average Depth

Average Depth = (Shallow End Depth + Deep End Depth) ÷ 2

Balance Tank Volume (ft³) = Basin Length × Basin Width × Basin Depth

Total System Volume = Main Basin Volume + Balance Tank Volume

US Gallons = ft³ × 7.48052  |  Litres = ft³ × 28.3168

In these formulas, Length (L) and Width (W) are the internal dimensions of the main basin at the waterline. Average Depth is the mean of the shallow end (D₁) and deep end (D₂). Basin Length (CL), Basin Width (CW), and Basin Depth (CD) are the internal dimensions of the catch basin at its operating water level. All measurements must use the same unit — feet or metres — to avoid conversion errors.

A calculation based only on the visible main basin will understate total water volume. For a 16 × 32 ft infinity pool with a 32 × 3 × 3 ft catch basin, the main basin holds 19,150 gallons (72,491 L), but the full system circulates 21,305 gallons (80,646 L). Dosing chemicals for 19,150 gallons when 21,305 gallons are in the loop leaves the system approximately 10% below target concentration.

Worked Example: 16 × 32 ft Infinity Pool

A 16 × 32 ft infinity pool is a common residential size that seats 6–8 swimmers and fits a standard backyard. The catch basin dimensions used here — 32 × 3 × 3 ft — represent a typical single-edge overflow trough. Actual tank dimensions vary by builder and site design.

How to Measure an Infinity Pool

Measuring the Main Basin

Measure length and width from internal wall to internal wall at the normal operating waterline. The overflow edge counts as one wall boundary. Do not include coping overhangs, tile lips, or deck edges — these are outside the water volume.

For depth, this calculator uses two measurements: the shallow end (D₁) and the deep end (D₂). Measure each from the waterline straight down to the pool floor. The calculator averages them for a sloped floor. If the pool has a flat bottom, enter the same depth for both fields.

Measuring the Balance Tank

The balance tank or surge tank must be measured separately using its own internal dimensions. Open the access panel and measure the interior length, width, and operating water level. Visible pool size from the deck gives no indication of the tank's actual capacity.

If builder drawings or engineering plans are available, use the dimensions shown there instead of estimating from access panels or exterior walls. Plans typically show the internal water volume of each component.

When an Estimate Is Acceptable

A percentage-based estimate is acceptable only when true tank dimensions cannot be obtained. Many residential infinity pools have a balance tank volume somewhere around 10–15% of the main basin volume, but the exact proportion varies by system design, overflow edge length, and surge capacity requirements. Treat percentage estimates as a starting point, not a final answer.

Infinity Pool Volume by Size — Reference Table

Main basin calculated as Length × Width × Average Depth × 7.48052. Balance tank calculated using Basin Length = pool length, Basin Width = 3 ft, Basin Depth = 3 ft as a comparison baseline — actual balance tank dimensions vary by system design. Average depth = 5.0 ft based on 3.5 ft shallow and 6.5 ft deep water. Use actual tank dimensions whenever available.

Residential infinity pools typically range from 12,000 to 33,000 total system gallons (45,000–125,000 L). The balance tank adds 9–15% to the main basin volume depending on pool size and trough dimensions. For a broader comparison across pool shapes, see the pool volume by size reference.

Typical Infinity Pool Sizes and Total Water Capacity

Residential infinity pools most commonly fall in the 14 × 28 ft to 20 × 40 ft range, holding between about 16,500 and 32,600 total system gallons (62,500–123,500 L). A compact 14 × 28 ft design fits narrow hillside lots and holds about 16,547 gallons (62,637 L) with a typical catch basin. A larger 20 × 40 ft pool suited for entertaining reaches about 32,615 gallons (123,461 L) total.

Two infinity pools with identical main basin dimensions can have different total system volumes. The difference comes from the balance tank — a deeper or wider trough holds more water and shifts the total upward. Hidden hydraulic components like overflow channels, equalization chambers, and connecting piping add small amounts of water that are difficult to measure exactly.

Visual design choices — perimeter-overflow versus single-edge, knife-edge versus slot-drain — affect the size and shape of the catch basin but do not change the need for an accurate water volume figure. Every gallon in the circulating loop requires the same chemical treatment regardless of how the infinity edge looks.

Why Infinity Pool Volume Affects Chemical Dosing Differently

Chemical dosing for an infinity pool must be based on total circulating water volume, not just the visible main basin. Chlorine, pH adjustment, algaecide, and calcium hardness calculations all rely on knowing how much water is in the active loop. Because the balance tank is part of that loop, ignoring it leads to systematic under-dosing.

On a 16 × 32 ft infinity pool, leaving out a 32 × 3 × 3 ft catch basin means dosing for 19,150 gallons (72,491 L) instead of the correct 21,305 gallons (80,646 L). That gap — 2,154 gallons (8,155 L) — is enough to reduce free chlorine concentration from a target of 3.0 ppm to roughly 2.7 ppm, which approaches the lower boundary of the recommended 1–3 ppm range.

For a full guide to adjusting chemical doses by pool volume, see pool volume and chemical dosing.

Why Total System Volume Also Matters for Circulation, Heating, and Refills

Circulation planning depends on all water in the active loop. A pump sized to turn over the main basin every 8 hours will take longer if the balance tank volume is not accounted for. On a system holding 21,305 gallons (80,646 L) total, a pump rated for 19,150 gallons provides a turnover cycle that is roughly 11% slower than expected.

Heaters and chillers move energy through the full water mass. A heater sized for a 19,150-gallon pool takes proportionally longer to raise the temperature of a 21,305-gallon system. For perspective on how average pool volumes affect heating time, the difference is equivalent to heating an extra 2,154 gallons (8,155 L) of cold water.

Refill planning after a partial drain, winterisation, or leak repair should account for every component in the overflow system. Water entering the main basin eventually fills the balance tank as well, so the total water needed is always more than the visible basin would suggest.

Common Mistakes When Estimating Infinity Pool Volume

1. Measuring only the visible main basin. The balance tank holds active, circulating water that must be included. A missing tank volume of 2,000–3,000 gallons (7,571–11,356 L) creates a persistent under-dosing gap.
2. Using outside wall dimensions instead of internal water dimensions. Concrete walls, tile finishes, and coping overhangs add 4–8 inches per side. Measuring from the outer shell overstates the main basin volume by 5–10%.
3. Entering a single depth for a sloped floor. Most infinity pools slope from a shallow end to a deep end. Using only the deep end depth overstates volume; using only the shallow end understates it. Enter both Shallow End Depth (D₁) and Deep End Depth (D₂) to get the correct average.
4. Assuming every infinity pool has the same balance tank percentage. Tank proportions depend on overflow edge length, expected bather surge capacity, and the engineer's design. A narrow knife-edge trough may hold 8% of the main basin volume; a large underground surge tank may hold 20% or more.
5. Treating a standard rectangular volume as the final total for an overflow system. A rectangular pool formula — Length × Width × Average Depth — gives the main basin only. An infinity pool always has at least one additional volume component that standard rectangle formulas do not include.
6. Measuring basin depth from the structural floor instead of the operating water level. The catch basin is not always filled to its structural top. Operational depth (CD) — the normal resting water level — is the correct input for volume calculation.

Frequently Asked Questions