Size effect is a major issue in concrete structures. Experimental and numerical investigations on the influence of size effect on crack opening, crack length and crack propagation are presented in this paper. An isotropic non-local strain softening damage constitutive law is adopted for the numerical model. The material characteristic length is calibrated using an optimization algorithm and a post-processing method is chosen to obtain information on cracking. Numerical global and local results are compared with the experimental data and conclusions are drawn on the advantages and limitations of the adopted modelling strategy to reproduce size effect in concrete structures.