How the math works
Pumpendium mathGallons per cycle = π × (diameter ÷ 2)² × pump-down depth ÷ 231 (cubic inches per gallon). Fill time = gallons ÷ inflow. Pump-out time = gallons ÷ (pump flow − inflow). Cycles per hour = 60 ÷ (fill time + pump-out time).
LimitsInflow changes through a storm; measure it when water is coming in fastest. Frequent short cycles wear switches and motors; a wider basin or a longer switch range lengthens each cycle.
Questions
How do I measure inflow?
With the pump unplugged briefly, time how long the water takes to rise one inch, then use the calculator's math in reverse: gallons in one inch of an 18 in basin is about 1.1. Plug the pump back in right away.
Why does my sump pump run so often?
A narrow basin, a short switch range or high inflow all shorten cycles. A check valve that leaks back also refills the pit.