A systematic approach is presented to estimate the roll separating force in bar rolling. This force is the product of the contact area between the rolled material and the roll pass, the mean unit pressure on the roll and the average flow stress within the roll gap. The contact area is determined by a computerized scheme based on a descriptive geometry approach. Also an approximate model to determine the average strain, hence the strain rate and the rolling temperature within the roll gap is proposed to estimate the flow stress from available material characterizations. The mean unit pressure on the rolls uses models existing in the literature pertinent to three-dimensional analysis of bar rolling. These models are slightly modified to encompass the unifying parameter expressing the geometry of the deformation zones, namely the ratio between the mean cross-sectional area and the contact area. The present approach is applied for a variety of common types of passes employed in bar rolling. Validation of the approach is realized through comparisons of predictions with a set of about 100 experimental and industrial data points for bar rolling in various passes. A fair agreement between the predictions and the measured data points is found. Reasons for the discrepancies are discussed. Furthermore a simplified analytical model to estimate the roll separating force which includes the least of adjusting empirical factors is suggested.