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 calculations.
Watt = Power Number x Density x Agitator speed3 x Rotor Diameter5
\begin{align*}
\rm P &= N_p n^3 \rho {D}^5 &&&\rm or &&&&& Np = {P \over pn^3 D^5}
\end{align*}
Where
P = Rotor power, Watt
Np = Power Number
ρ = Density of liquid, kg/m3
n3 = Rotor/agitator speed measured in revolutions / second
D5 = Rotor/impeller diameters in meters
Remember that Power Number decreases with an increase in Reynolds number. Read articles to be downloaded on the first page.