In high precision and heavily loaded spur gears the effect of gear errors is negligible, so the periodic variation of tooth stiffness is the principal cause of noise and vibration. High contact ratio spur gears could be used to exclude or reduce the variation of tooth stiffness. The analysis of static and dynamic transmission error of spur gears cut with standard tools of 20° profile angle is presented in this paper. A simple method to design spur gears with a contact ratio nearly 2.0 is used. It consists of increasing the number of teeth on mating gears and simultaneously introducing negative profile shift in order to provide the same center distance. Computer programs to calculate static and dynamic transmission error of gears under load have been developed. The analysis of gears using these programs showed that gears with high contact ratio have much less static and dynamic transmission error than standard gears.