TradesHow this works
A sump pump is sized by two numbers: how fast water comes into the pit, and how hard the pump has to push it out. This tool takes your measured inflow, adds a storm safety factor, works out the total head from the vertical lift and the discharge run, and then finds the smallest pump horsepower whose curve still delivers that flow at that head.
Bigger is not automatically better. Once the flow is covered, the thing that protects the pump is a pit large enough to keep it from short-cycling and a backup pump for the storm that knocks the power out. Confirm the pump you buy on its own performance curve.
Common questions
How do I measure my pit inflow?
During heavy rain, unplug the pump, let the pit fill to the on level, then time how many inches the water rises in one minute. Multiply the inches per minute by the pit gallons per inch (about 1.1 for a standard 18 inch pit) to get gallons per minute. That measured inflow is the starting point.
Why multiply inflow by 1.5?
The inflow you measure is a normal rain event. The safety factor covers the heavier storm that will eventually come, so the pump keeps up instead of letting the pit overflow. Going much higher just oversizes the pump and makes it short-cycle.
Is a bigger pump always safer?
No. A pump that empties the pit too quickly turns on and off constantly, and that short-cycling wears out the motor and switch. Match the flow you need, then reduce cycling with a larger pit, not more horsepower. The real resilience upgrade is a battery or water-powered backup pump.
Sources: Sump sizing method: 1.5x measured inflow, total dynamic head = lift + discharge friction, matched to typical residential pump curves (SupplyHouse, RadonSeal, Zoeller). Confirm the actual pump curve.. Engine version 1.0.0. Risk tier 2.