This paper will present a new method of determining the contact stress and theoretical life of bearings under transmission gears. For reference, a short table showing examples of this method applied to current production transmissions is included. Further, there is a brief summary of the controlled experiment that was used to determine which bearing parameters most Influence stress and life. Finally, a “Designers Guide” and discussion are presented to be used as a reference when initiating or evaluating a bearing layout.The methods traditionally used by transmission designers for calculating capacity requirements and theoretical life of roller bearings in planet gears, idler gears or constant mesh gears have not taken into account many of the factors which are important to the life of the bearing. This paper is intended to present a new approach in calculating bearing stress in these applications. A report on a study of influential factors is included.