Various test methods can be used to determine the strength of ceramic glasses. For beam-shaped specimens, for example, the Four-Point-Bending test (4PB) is used, while for disc- or plate-shaped specimens the Ball-on-Three-Balls test (B3B) or the Ring-on-Ring test (RoR) is applied. However, as specimens become thinner, proportionally higher deflections are required to initiate fracture due to reduced flexural rigidity. This often leads to geometric limitations in the applicability of such tests. Therefore, new testing or evaluation methods are needed to determine the strength of thin fibres or substrates. In this work, the strengths of glass wafers AF 32® eco from Schott were determined using the already mentioned test methods (4PB, B3B and RoR) based on the Weibull theory. Furthermore, finite element methods (FEM) were carried out for the Ring-on-Ring test in order to analyse possible deviations from geometric linearity. In addition, a Two-Point-Bending test (2PB) was developed and its results validated. All experiments showed that the strength values depend very much on the final machining condition of the samples and less on the material itself. Furthermore, it was found that thin specimens sometimes show significant deviations from a linear deformation state. This was shown by FEM calculations for the Ring-on-Ring test. Here, the characteristic strength is estimated to be three times higher according to standard evaluation than it occurs according to FEM calculations. The stress distribution within the specimen also shows clear differences to the theory. Although this behaviour was not checked for the Four-Point-Bending test and the Ball-on-Three-Balls test, it can be assumed that certain deviations also occur. The Two-Point-Bending test offers a simple way of characterising the strength of thin glasses. Here, disturbing contact forces due to a support are completely avoided. The evaluation also shows that the strength values match very well with those from the Four-Point-Bending test.