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Specific requirements on the specimen geometry necessary for the determinationof fracture mechanics parameters for polymers by using the instrumented Charpyimpact test are summarized. As examples, the influences of the specimen thickness and a/Wratio are considered. For characterizing the geometry independence of fracture mechanicsparameters, geometrical factors are used, which make possible an estimation of the requirementson the specimen geometry without any further experiments. For polymers, theexperimentally determined geometrical factors vary in a wide range; this means that theuse of constant geometrical factors must cause a pronounced under- or overevaluation ofthe requirements on the specimens. The relationships between geometrical factors andfracture mechanics parameters, which were found to be generally valid for polymers, areindependent of the kind of loading (static, impact-like) and the crack propagation behaviour(stable, unstable).