A yield locus obtained with the Jenike Flow factor tester can be represented by the Warren Spring equation. In this equation σ and π are the normal and shear stresses respectively, C and T the cohesion and tension, and N a curvature parameter constant for one material. Based on this equation and assuming a constant ratio K = C/T, several partly graphical partly numerical solution methods are known. The pure numerical method described in this article has several advantages over the graphical methods used so far. The method presents precise objective results, acquired directly from the measured data. No more or less subjective manipulations are required. Although the method seems rather complicated, the required number of iterations is relatively low because of the rapid convergence of the iteration process. This leads, together with the simplicity of the formulas used, to a relatively small computing time. It appears that with the assumption of a constant ratio K = C/T for one material, all data reqired for the Jenike hopper design method can also be computed purely numerically by means of a least-squares method using Newton's zero finding thus required are not influenced by the initial estimations. The results obtained are only a function of the measured points and interpretative errors are eliminated.