Infinity Edge Calculator
Catch basin sizing and pump requirements for vanishing edge.
About this calculator
Infinity Edge Length (ft) and Overflow Depth (inches) combine through the broad-crested weir formula (Q = C x L x H^1.5) to set Calm Weir Flow (GPM) -- and because that H term is raised to the 1.5 power, Overflow Depth matters more than its small fraction-of-an-inch range suggests: doubling the overflow sheet from 1/4 in to 1/2 in nearly triples the flow, not just doubles it. Wind Exposure then scales that calm flow up further (1.0x sheltered, 1.25x moderate, 1.5x exposed) to produce Design Flow Rate (GPM), the number the edge pump actually has to be sized for -- and Wind Exposure separately inflates Catch Basin Volume (gal) through its own bather-surge-style term, so a windier site needs a bigger basin for two independent reasons layered on top of each other, not one.
Pool Volume (gallons) only feeds the catch basin's 5% bather-surge allowance -- it has no effect on weir flow, wind factor, or pump sizing at all, since those are governed entirely by the edge's own dimensions and the site's exposure. At high enough Design Flow Rate (GPM) and Total Dynamic Head (ft) -- a long edge, a deep overflow sheet, high wind exposure, and a tall edge drop together -- the calculated pump horsepower can run well past the largest 10 HP standard motor this calculator lists; rather than silently recommending 10 HP as if it were an adequate answer at that scale, the calculator flags it, since what that flow actually needs is multiple parallel edge pumps or an engineered commercial pump skid, not one oversized residential motor.
Inputs
Results
Design flow rate (GPM)
232.4
Edge pump exceeds single-motor max
No
How to Use This Calculator
- Enter the infinity edge length in feet — the total span of the vanishing edge.
- Set the overflow depth in inches (the water sheet thickness over the edge; 3/8 inch is typical).
- Enter the total pool volume in gallons for surge basin sizing.
- Set wind exposure: 1 = sheltered courtyard, 2 = typical backyard, 3 = exposed hilltop or coastal.
- Enter the edge drop height from the pool deck to the catch basin floor.
- Review Design Flow Rate (GPM), Catch Basin Volume, and Edge Pump HP to specify equipment.
How the result changes with Overflow depth (inches)
| Overflow depth (inches) | Design flow rate (GPM) | Edge pump exceeds single-motor max |
|---|---|---|
| 0.19 | 82.5 | No |
| 0.28 | 150.8 | No |
| 0.56 | 427.6 | No |
| 0.94 | 919.6 | Yes |
What each input means
- Infinity edge length (ft)
- Length of the vanishing edge where water flows over.
- Overflow depth (inches)
- Depth of water sheet flowing over the edge. Typically 1/4 to 1/2 inch for visual effect.
- Pool volume (gallons)
- Total pool water volume for surge calculations.
- Wind exposure (1=low, 2=med, 3=high)
- Wind exposure level. Hilltop or coastal = high; sheltered courtyard = low.
- Edge drop height (ft)
- Vertical drop from the pool edge to the catch basin floor.
What each result means
- Design flow rate (GPM)
- Flow rate the edge pump must handle, including wind surge factor.
- Calm weir flow (GPM)
- Flow rate over the edge under calm conditions.
- Catch basin volume (gal)
- Minimum catch basin (surge tank) capacity in gallons.
- Catch basin footprint (sq ft)
- Catch basin surface area assuming 3 ft depth.
- Edge pump (HP)
- Recommended pump motor size (next standard size up).
- Total dynamic head (ft)
- Total head the edge pump must overcome.
- Calculated HP (exact)
- Exact calculated horsepower before rounding to standard size.
- Edge pump exceeds single-motor max
- True when Calculated HP (exact) exceeds the largest standard 10 HP motor listed — at that scale, use multiple parallel edge pumps or an engineered commercial pump skid rather than one oversized residential motor.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersInfinity edge length (ft) = 25, Overflow depth (inches) = 0.375, Pool volume (gallons) = 15000, Wind exposure (1=low, 2=med, 3=high) = 2 = 5 input(s) provided
- Calculate Design flow rateDesign flow rate = flowGPM * windFactor232.4 = 232.4
- Calculate Calm weir flowCalm weir flow = flowCfs * 448.83186 = 186
- Calculate Catch basin volumeCatch basin volume = max(200, transitVolGal + surgeAllowanceGal + windSurgeGal)1515 = 1515
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does a small change in Overflow Depth (inches) move the flow rate so much?
Because the weir flow formula (Q = C x L x H^1.5) raises the overflow depth to the 1.5 power, not a simple linear factor. Going from a 1/4 in overflow sheet to a 1/2 in one -- doubling the depth -- multiplies Calm Weir Flow (GPM) by roughly 2.8x, not 2x. That's why this calculator keeps Overflow Depth (inches) in a tight 1/8 to 1 in range: even small adjustments there have an outsized effect on the flow, and hence the pump and catch basin, everything downstream is sized to.
Why does Wind Exposure affect both the pump size and the catch basin size?
They're two separate mechanisms that both key off the same input. Wind Exposure multiplies Design Flow Rate (GPM) directly (1.0x/1.25x/1.5x for sheltered/moderate/ exposed), which is what the edge pump has to be sized to handle. Separately, it also adds its own wind-surge allowance to Catch Basin Volume (gal), on top of the fixed 5% bather-surge allowance every configuration gets. A windy site needs both a bigger pump AND a bigger basin, from two different terms in the formula.
I have a small plunge pool but a long, deep-overflow infinity edge -- will the pump still be undersized?
No, not on account of pool size. Pool Volume (gallons) only feeds the catch basin's 5% bather-surge allowance in Catch Basin Volume (gal) -- Design Flow Rate (GPM), Total Dynamic Head (ft), and Edge Pump (HP) are all driven by Infinity Edge Length (ft), Overflow Depth (inches), Wind Exposure, and Edge Drop Height (ft) instead. A small pool with a long, deep-overflow edge can need a larger pump than a much bigger pool with a modest edge.
What does 'Edge pump exceeds single-motor max' mean?
It means Calculated HP (exact) came out higher than the largest standard 10 HP motor this calculator lists -- which happens with a long edge, a deep overflow sheet, high wind exposure, and a tall edge drop combined (for example, a 100 ft edge at this calculator's maximum overflow, wind, and drop settings computes roughly 500 HP, not 10). At that scale, a single residential-grade pump motor is the wrong answer regardless -- multiple parallel edge pumps or an engineered commercial pump skid is what the flow actually needs, which is why the calculator flags it instead of quietly showing "10 HP" as if it were adequate.
Related Calculators
The questions that sit next to this one — chosen by subject, including calculators filed under a different category.
Catch Basin Spacing Calculator
Calculate maximum catch basin (inlet) spacing based on gutter flow capacity, cross slope, and design rainfall intensity.
Pool ConstructionPool Plumbing Calculator
Pipe sizing and plumbing materials for pool circulation.
Pool ConstructionPool Excavation Volume Calculator
Cubic yards for pool dig from shape and depth.
Pool ConstructionRebar Grid Calculator
Rebar quantity for gunite/shotcrete pool shell.
More in Construction & Building Trades.