It is required to design a pair of spur gear 20 deg full depth involute teeth. Take number of teeth on pinion 18 and gear ratio= 4/1 The input shaft rotate at 1440 rpm and receives 10KW. Both gears are made by steel material with sigma b = 200MPa .Take Cs = 1.5 FOS = 1.5 Y = 484 - 2.86/2 Design gear by using velocity factor is in account with velocity 5m /sec and check the design by calculating correct factor of safety.