This paper aims to present a numerical model to calculate the power losses due to the friction phenomenon in spur geared transmissions which are highly used in many domestic and industrial applications. Since the increase of the power to be transmitted at high rotational speeds result in significant power losses and wear phenomenon, the latter must therefore be taken into account during the different phases especially when designing and choosing the materials of the gears since power losses have direct impact on the lifetime of the power transmitters. The present work gives a better understanding of how to numerically evaluate the friction power losses in spur gears and it is a preliminary study to the future work where the impact of friction and wear phenomena on the material lifetime and energy consumption will be discussed.