Present paper proposes a universal resistance equation relating friction factor (λ), the Reynolds number (R) and roughness height (k) for the entire range of turbulent flow in pipes covering all the three regimes: smooth, transition and rough. Experimental data of Nikuradse and others were used. Such an equation is found to be sufficient to predict the friction factor for all ranges of R (≥4000) and different values of k. Present model is found to be equally valid for both cases of commercially available pipes and Nikuradse experiments on sand roughened pipes