Computer Aided Design and Optimization are two important directions of present research activity in spur gears. A review of literature indicates that the methods available, are iterative and rather tedious. In present work the non-linear optimization problem with the minimum centre distance as an objective function has been addressed. A new design space in terms of module and pinion number of teeth has been defined. Empirical relations to obtain Feasible Optimal Centre Distance based on input torque and gear ratio for 20° pressure angle for 20 gear materials, obtained by regression analysis, have been reported. A simple nomograph has been developed which gives pinion number of teeth and standard module.