This paper concentrated on the effect of contact ratio on the contact stresses generated on meshing spur gear teeth during the power transmission. In this study, various contact ratios of spur gear teeth have been analyzed. For this contact ratio considered, the rate of loads sharing and angular position of loads were determined on the involute profile of meshing tooth of each gearing. In addition to that, the different stress conditions of this tooth for the critical position (at the instant when the generated contact stress is at the maximum state) are determined. From this study, it is clear that the highest contact ratio resulted in the lowest generated tooth stress (i.e. the highest load-carrying capacity). This approach reduced the contact stresses for power transmission. At last, the results obtained from Hertz’s contact stress formula and AGMA contact stress formula, and then compared allowable stress. They are comparable to each other.