The way to properly account for variations in operating center distance and in functional tooth thickness are not obvious. The method presented here will give a good estimate of the range of operating backlash, provided the range of operating center distance and the range of operating functional tooth thickness is known. A method of estimating the functional tooth thickness from a combination of the nominal tooth thickness range and the elemental tolerances are presented. In unidirectional or bidirectional cases, gears have a certain amount of space usually called "backlash" between meshing teeth flanks are allowed for functional reasons. While backlash is a requirement for efficient performance of a gear pair under lubrication and possible occurrence of interference duties, it is also a hard to control parameter under manufacturing, and assembly errors, heating of the gearbox elements. However, optimum/correct value of the required backlash is not well defined and calculated before the actual gear pairs are put into operation. Researchers and engineers who study on power transmission field, mechanical design, and controlling field have been focused to backlash by investigating its influence onto gear behavior, predict, remove, minimize, and optimize. In this approach, probabilities of minimum backlash configurations have been performed creating adjacent pitch deviation document which is effectful parameter based on manufacturing reports approximately via MATLAB. Thus, how backlash is minimum could via certain configurations between gears have been evaluate using phasing methodology under defined contact teeth which are provides minimum backlash chance.