Size a sump pump from inflow rate, lift height and basin capacity.
Capacity is set above peak inflow so the pump can gain on the water rather than merely keep pace. Cycle frequency matters because excessive starting is what wears the motor out. Pump curves fall steeply with head, so a pump rated at the required flow at zero lift may deliver less than half of it at three metres.
Sump Pump
Pump capacity = peak inflow × 1.5; total head = lift + friction losses
Pump capacity = peak inflow × 1.5; total head = lift + friction losses Capacity is set above peak inflow so the pump can gain on the water rather than merely keep pace. Cycle frequency matters because excessive starting is what wears the motor out.
Pump curves fall steeply with head, so a pump rated at the required flow at zero lift may deliver less than half of it at three metres.
This calculator takes 5 inputs: Peak water inflow, Vertical lift, Discharge pipe length, Basin volume, Pump efficiency. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.