The modern Russian methods for defining the mechanical characteristics of brick masonry are based on finding the strength of masonry components (brick and mortar). After getting the results of laboratory tests of components, mechanical characteristics of masonry are calculated using empirical formulae. Those formulae, however, cannot take into consideration the presence of damages and other factors. Obtaining the characteristics (strength and deformation) by a direct flat-jack test of masonry fragments on-site looks promising. A widespread use of FEM requires setting accurate deformation features for modeling domes, arches and thin brick outside layer in multilayer walls. Also accurate deformation characteristics are used for calculating temperature loads. The paper gives the results of practical use for the masonry deformation research by the flat-jack test method. The correlation factors are defined and rigidness coefficients of flat-jacks are obtained in the study.