Power Number calculator

This online calculator give instant answers 

Power Number is a dimensionless parameter based on the power in Watt consumed by the agitating rotor = impellers for the SUB and turbines for the SUF. Use the below online calculator to easen up your own calculations.

Power Number
Density in gram/dm3
Revolutions-Per-Minut - RPM
Rotor diameter in mm


Watt = Power Number x Density x Agitator speed3 x Rotor Diameter5


    \rm P &= N_p n^3 \rho {D}^5 &&&\rm or &&&&& Np = {P \over pn^3 D^5}


P = Rotor power consumed in Watt
Np = Power Number
ρ = Density of liquid, kg/m3
n3 = Rotor / agitator speed measured in revolutions / second
D5 = Rotor / impeller diameter in meter's


  • That Power Number decreases with an increase in Reynolds number. Read articles to be downloaded on page - "Power Number definition".
  • To subtract from total motor power the friction in various bearings, motor, coupling, electrical losses, etc. from total motor power.