A simple and handy calculation method of the force ratio of a bolted joint is proposed. This method is applicable not only to symmetrical but also unsymmetrical bolted joints. The process of this method is as follows: First, the clamped plate of a bolted joint subjected to an external force is divided into two parts; in one part, the clamping force is increased by the applied external force, whereas in the other part, the clamping force is decreased. Next, the above two parts are respectively replaced by two springs of which spring constants are equivalent to those of the two parts. Third, the bolt is replaced by a spring of which spring constant is equivalent to that of the bolt. Finally, the bolted joint is modeled as a structure which is constructed with all spring elements. The expression of force ratio is derived from the equilibrium of the forces acting on the above model and the condition of compatibility of deformation of the model. From the viewpoint of the design calculation of bolted joints, the results of the calculation according to the above method agree satisfactorily with the solution from the three ―dimensional theory of elasticity and the experimental results.