The edge strength of glass is influenced by the size of the surface (near the edge) which is subjected to tensile stresses. To quantify this size effect, 8 series of single layer annealed glass beam specimens (as-received glass) were subjected to in-plane four-point bending with linearly increased loading until failure. Within the 8 series, the edge finishing differed between ‘cut’ and ‘ground’, the thickness between 4 and 8 mm and the beam length between 550 and 1100 mm. From the test results a reduction in strength was observed for increased specimen size, which is in line with common expectations. However, the analytical prediction of this reduction by probabilistic laws derived from the literature is unsafe. In fact, these predictions of the strength reduction were up to 14% less conservative than those observed from the presented test results. From this it is concluded that future standards should estimate the size effect more conservatively than currently done by the existing laws in the literature.