How to use this sump pump size calculator
Sump pumps should be selected by the flow they must handle at the actual total head, not just by horsepower. This calculator turns a measured inflow rate into a target pump capacity with a safety margin.
How the estimate works
The tool multiplies measured inflow by your chosen safety factor, then estimates additional head from vertical lift and pipe run. The result is a target gallons-per-hour capacity at that approximate head. Always confirm the pump curve for the exact model.
What the result does — and doesn’t — tell you
Use the result as a first-pass planning number. Real projects and equipment choices can change because of local prices, codes, product specifications, site access, material condition, labor, taxes, disposal fees, permitting, or engineering requirements.
- Recheck your measurements and use the actual project or equipment specifications whenever they are available.
- Compare the estimate with at least one real supplier, contractor, rental company, manufacturer chart, or local authority before committing money.
- Leave room for taxes, permits, delivery, disposal, site preparation, upgrades, or other items that are not visible in a simple online calculator.
Before you act on the result
Sizing errors can cause poor performance, short cycling, overflow, insufficient capacity, or unnecessary equipment cost. Use the result to narrow the range, then verify it against manufacturer data, local code, and a qualified installer or designer. When a formal load calculation, pump curve, soil test, or permitting rule applies, that professional information should control the final choice.
Use sizing calculators as a starting point
- Measured inflow (gallons/min): A measured inflow during a wet event is more useful than choosing a pump only by horsepower.
- Vertical lift (ft): The pump must overcome the elevation difference from the sump water level to the discharge point.
- Horizontal discharge run (ft): Long pipe runs and fittings add friction and reduce delivered flow.
- Safety margin: Extra capacity helps account for heavier storms, measurement uncertainty, and changing conditions.