This paper presents a method for grasp evaluation. It is based on the ability of the grasp to reject disturbance forces. The procedure takes the geometry of object into account, and it is also possible to incorporate task-oriented information. The evaluation criterion is formulated as a min-max optimization problem, for which an efficient algorithm is proposed and analyzed. The result of this algorithm is independent of scale and choice of reference frame, and can easily be visualized as a surface in the force space. The method is illustrated with several examples.