Wide use of various porous materials in construction engineering applications requires development of up to date methods of non-destructive characterization and optimization of such materials. This work explores an approach to effective elastic modulus calculation of a brittle porous material. Available 3D digital data on the specimen geometry is converted into finite element uniform mesh consisting purely of elements of cubic shape. The resolution limit is determined that allows for analysis of effective properties of porous materials without a significant loss of accuracy. This should facilitate resolving the question on the representativeness of the specimens considered and also increase the speed of the solution process for similar tasks. The approach described can be used for modeling of uniform construction materials, also materials with inclusions under the assumptions of geometrical and material linearity.