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Sump Pump Size Calculator
Quick answer: Enter your pit diameter, how many inches the water rises in one minute during heavy rain, your vertical lift, pipe run and elbows, and a safety margin. The calculator estimates inflow in GPH and the head the pump must overcome, giving a target such as "600 GPH at 12 feet" to check against pump curves.
How it works
The pit's gallons per inch is π × (diameter ÷ 2)² ÷ 231. Multiplying by the rise in one minute gives gallons per minute; times 60 gives gallons per hour. The margin adds headroom for wetter storms and pump wear. Head is estimated as vertical lift plus about 1 foot per 10 feet of 1½-inch pipe, 0.5 foot per elbow and 2 feet for a check valve — common planning rules of thumb, not measured friction.
How to measure rise
Measure on a wet day. Mark the level when the pump stops, then time one minute and measure how far the water climbs. If the pump starts before a minute passes, measure the rise over the shorter time and scale it up.
Worked example
An 18-inch pit (about 1.10 gal/in) rising 5 inches per minute gives about 5.5 GPM, or 330 GPH. A 50% margin makes the target about 496 GPH. Nine feet of lift, 25 feet of run, three elbows and a check valve gives roughly 15 feet of head, so the shopper looks for at least ~500 GPH at 15 feet.
Illustrative note (2026-10-29): Default inputs and this example were set on 2026-10-29 for illustration; they are not data from a real home.
Limits
This is a planning estimate. It does not model your exact pipe, valve or pump curve and cannot predict future storms. Have a licensed plumber confirm sizing, and a licensed electrician confirm circuits.