The power input of a centrifugal pump (pump input power) is the mechanical power taken by the pump shaft or coupling from the drive. The SI unit of measurement for power input is watts (W). Input power
Calculation must be based on the flow rate (Q) at the inlet cross-section of the centrifugal pump if the fluid handled exhibits substantial compressibility. Pump input power can also be defined more precisely in conjunction with centrifugal pumps.