Over the last century, polymeric materials have become ubiquitous and can now be found in a wide variety of everyday products. Due to the dramatically increasing environmental pollution by plastics, use of polymeric materials has become as subject of societal criticism. Further, the production of polymer products is energy-demanding because the raw material must be plasticated before shaping. Injection molding and extrusion are the most common processing techniques for producing finished and semi-finished polymeric products. Since most of the energy required by these processes is provided via the screw, knowledge of the axial screw-torque profile would help to optimize production and make it more energy-efficient. However, no satisfactory measurement technique has to date been developed for measuring the length-based torque of industrial single-screw extruders. In this paper, we present a novel method that measures the torque – and therefore the mechanical energy input over the screw length – by means of laser-beam deflection. We first analyzed existing torque measurement techniques and evaluated their applicability to industrial single-screw extruders. We then developed a prototype for measuring screw torque by laser-beam deflection, which we tested on an industrial-scale 35/34D single-screw extruder processing a high-viscosity pipe-grade polypropylene. Our measurement results are promising and show very good agreement with the calculated maximum screw torque.