A design tool for passive wrist support using compliant spatial beams as gravity balancer is presented. The aim of this assistive device is to reduce required effort for pronation-supination and flexion-extension by 70% to help patients with muscular weakness keeping their hand’s posture and doing daily tasks, while the forearm is rested. To reach this goal, a setup with three connection points to the user’s hand, and two optimized spatial beams as elastic gravity compensators, are developed. The overall shape and cross-sectional dimensions of the compliant beams are attained using an optimization technique. The objective is reaching a desired endpoint kinetostatic behaviour which is determined based on the hand’s weight and available muscular forces. A design case is presented to show the ability of the method, and the final errors from the desired behaviour are clarified. In the end, possible further applications of the design tool are discussed.