Workpieces, which are fed to grinding in a lot, have respective dimensions generated in the previous stage of production and then the stock allowance of each workpiece is distributed in the lot. In this paper, the effects of variations of stock allowance upon dimensional accuracy are theoretically analyzed, based on the accumuration phenomenon in grinding, in case that workpiece dimensions are normally distributed in the lot, by investigating the dimensions of ground parts and their distribution, and the relation between the infeed position of grinding wheel and the percentage of defective products in dimension. It has been made clear that the dimensions of ground products have a close relation to the plunge speed, the sparkout grinding time and the workpiece dimension, that the distribution of product dimensions is not normal and affected by the plunge speed, the sparkout grinding time, the stock allowance and its variance, and that the proper selection of infeed position of grinding wheel makes the percentage of defective products in dimension minimum.