Abstract: Calculation of bending and pitting strength of gear drive is one of the important concerns towards the efficiency improvement program in modern industries. Some preliminary experiments uses calculation methods based on uniform load distribution model on the gear teeth.The results obtained by such experiments are not parallel to recent estimations based on the non-uniform load distribution on gear teeth. Due to different mesh stiffness on different load points, non-uniform load distribution is the actual loading condition. American Gear Manufacturers Association(AGMA) and ISO standards assumes uniform model of load distribution which is not accurate. In order to create coherence among the results obtained by AGMA and ISO, a number of modifications factors have been applied in derived mathematical relations for gears. Latest methods such as minimum elastic potential energy method have been introduced to overcome drawbacks of these mathematical relations.This review article highlights a number of such methods in chronological order so that reader may obtain a overview of contribution of various scientists in development of gears having least bending and contact stress.