This disclosure presents a dimensionless relationship between a fluid flow rate, a viscosity, and a brake horsepower (BHP) in a pump operation and a method that uses the dimensionless relationship to predict a BHP for viscous performance of a pump from water performance specifications. Using the dimensionless relationship, i.e., K-R number, the methods determine a BHP correlation that allows the prediction of the BHP specification to satisfy a pump performance metric at any given speed, flow rate, and viscosity. This prediction can be calculated from water performance specifications without physically testing the pump in the viscous implementation environment.