Fiber reinforced plastics are widely used in the field of lightweight applications and especially in the mobility sector, due to their good weight-specific mechanical properties. During the processing of short and long fiber reinforced plastic, fiber breakage occurs due to fiber-fiber and fiber-polymer interaction as well as contact between fibers and the machine surfaces. This degradation in fiber length results in a decreasing reinforcing effect and lower mechanical properties. In the experimental investigations the influence of fiber geometry and sizing on fiber breakage is investigated. Therefore, different chopped glass strands are compounded into a polyamide 6 (PA6) using a twin-screw extruder. The chopped glass strands differ in initial length, diameter, sizing chemistry, glass type and cross section geometry. For all material blends the same screw configuration and screw speed is used. To measure the occurring fiber breakage in the different material blends, melt samples are taken at the die plate and an underwater pelletizer is used to produce pellets for each blend. For each material the fiber length is measured in the melt sample as well as in the pellets. The different material blends are then processed on an injection molding machine and tensile test specimens are produced. The mechanical properties determined by testing these specimens are compared with each other to identify to which extent the fiber parameters influence the tensile strength and modulus and how strong the influence of the fiber length is on these properties.