Accurate prediction of power consumption of impeller in ail aerated vessel is crucial for a successful scale-up, operation, and design of reactors in general. A mechanistic model with a correlation that can accurately predict power consumption was developed. Taking into account both geometrical parameters and physical properties of the working fluids, this model reduces the number of adjustable parameters better than published empirical relations. It has the advantage of allowing the user to easily scale up agitated vessels and to evaluate power consumption even for large-scale equipment. It has been tested only for Rushton turbines, however, because it is simply based on mass balances, energy balances and continuity equations, it could also be implemented for use with other impellers with very, few modifications.