Parameters characterising the structure of porosity of building material are very difficult to be considered analytically with a sufficient level of accuracy. Nevertheless, the knowledge about the geometric characteristics of the pore-capillary structure of materials is essential for modelling the moisture transfer process. Therefore, we propose the original dependence for determining the coefficient of tortuosity of pores and capillaries which take part in capillary moisture transfer in building materials of homogenous and isotropic porosity structure. The equation was developed on the basis of the general conductivity theory and the capillary theory. A comparative analysis of the proposed, theoretically justified equation, and other equations as well as experimental data shows, that the proposed dependence is the most useful for determining the tortuosity coefficient applied in calculating moisture transfer process in capillary-porous materials. (c) 2012 Elsevier Ltd. All rights reserved.