Sump Pump Cycle Calculator

The fill time is the switch volume (the water between the pump turn-on and turn-off float levels) divided by the inflow rate. The run time is that switch volume divided by the net pumping rate, which is pump flow minus inflow. Adding fill time and run time gives the full cycle time, and 60 divided by that gives cycles per hour.

It is the volume of water held in the sump pit between the float switch on and off levels. You can estimate it from the pit cross-sectional area times the vertical distance the float travels, converted to gallons, or measure it directly. Enter that switch volume in gallons; it sets how much each cycle moves.

Inflow is how fast groundwater enters the pit, which varies from a trickle in dry weather to a heavy flow during storms. High inflow shortens the fill time and lengthens the run time because the pump fights incoming water. If inflow approaches or exceeds the pump flow, the pump runs continuously and may not keep up.

Frequent short cycles wear the float switch and motor. A larger switch volume, achieved with a wider pit or a greater float travel, reduces cycling. This calculator reports cycles per hour so you can compare configurations, but follow the pump manufacturer's guidance for acceptable cycling on your specific unit.

If the inflow rate equals or exceeds the pump flow rate, the pit fills faster than the pump can empty it, the water level rises continuously, and the pump cannot complete a cycle. This calculator flags that case as not applicable, signaling you need a higher-capacity pump or a second pump for that inflow.