Geometric Parameters of Gears are mainly driven by two parameters, 1) tooth bending strength & 2) surface durability (pitting). Gear design software (KISSSOFT / ROMAX) propose options on gear parameters for gear pair with result of tooth bending strength & surface durability. This paper does not describe the Gear design software application for optimization of geometric parameters of the gear tooth. It explains the engineering method for Gears parameter optimization.Without using gear design software, optimization of gear geometric parameters is possible by using the gear parameters of existing gear pair. Geometric parameters of existing gear are derived by span measurement method. The geometric parameters such as, Module, Helix angle, Tip/Root diameter, Face width & Tooth modification are optimized by using below parameters derived from existing gear pair Contact RatioTooth thickness ratio on working PCD for Pinion & Gear(Working PCD-Root Diameter) per module factor for Pinion & GearTip Clearance coefficient for Gear & PinionThe paper also describes a standard procedure to arrive at the optimized geometric parameters for the gear pair.This is cost effective method to arrive at optimized solution in absence of gear design software. Even in presence of gear design software's we can reduce the number of iterations by using this method.