Local values of shear stress at the tool-workpiece interface in plane-strain upsetting were determined from experimental observation of the distorted grid pattern. The friction condition at the interface was formulated and used to develop the slip-line net. This slip-line net was used to predict the geometry changes of the free boundary. Results of this method showed good agreement when compared with those obtained experimentally. Using Hencky’s equations, the normal pressure was determined at the interface. From the normal pressure values, the load was calculated and compared to that measured during experiment.