This paper discusses a methodology for sizing air muscles to be used in the implementation of a robotic arm. By a complete evaluation of the arm kinematics and dynamics, the developed methodology assures a fast and correct sizing of the air muscles required to satisfy the arm specifications. This methodology was applied to a robotic arm capable of lifting 5 [kg] in the worst case. The results obtained by the use of the sizing algorithm are fully satisfactory. © 2011 IEEE.