Marxman's diffusion-limited analysis of hybrid rocket combustion has been often used to investigate various combustion problems in hybrid rocket motors. This analysis was developed on the basis of the Reynolds analogy in turbulent boundary layers. This analogy assumes that both molecular and turbulent Prandtl numbers are equal to one. In the present study, a semi-empirical correlation between the Stanton number and the skin-friction coefficient in a turbulent boundary layer was obtained. This is applicable to hybrid rocket combustion, and also includes the effects of the Prandtl numbers variation. Using this correlation, a fuel regression rate equation for standard-flow hybrid rocket motors was obtained, and its characteristics were examined. In addition, the calculated regression rate characteristics were compared with the experimental data from the laboratory-scale hybrid rocket motors that used gaseous oxygen (GOX) as oxidizer and polymethylmethacrylate (PMMA) as fuel.