The bending strength of glued laminated timber is size dependent. It is well known that one reason is the scatter of the material properties due to the natural growth characteristics of timber which leads to a size effect according to the Weibull weakest link theory. In this paper, it is demonstrated that glued laminated timber also exhibits the size effect associated with a quasi-brittle material behavior. Experimental tests on glued laminated timber beams in different sizes are compared with finite element simulations. The specific distribution of weak links in each beam was included in the simulations. In this way, the Weibull type size effect is automatically taken into account. The simulations which consider quasi-brittleness through the constitutive law were able to predict well the outcome of the experiments over the full range of beam sizes.