A non-contacting bale size sensor (80) for an agricultural round baler (10) having bale-forming chamber (20) partially defined by a plurality of continuous side-by-side belts (70) trained around a plurality of fixed guide rolls (43-47,49) and at least one moveable roll (53, 54) connected to a belt take up arm (51). The bale size sensor (80) detects the position of the belt take up arm (51) by measuring distance between a fixed position and the take up arm (51) and a connected control unit (90) determines the size of the bale (100) within the bale-forming chamber (20).
