In this study, masonry strength and toughness sensitivity to the brick/block unit size is studied. Meso-analyses of masonry wall parts are performed to obtain macroscopic constitutive behaviour. Subsequently macro-analyses of base-restrained shrinking masonry walls are performed to study the sensitivity of the wall under this loading condition to the unit size. Computational models for masonry developed over the past decade and recently implemented in DIANA are employed for the analyses. The results reveal how these geometrical and material parameters affect masonry behaviour in terms of composite strength and toughness, as well as crack initiation and crack propagation.