Without special technologies, it is rather difficult to determine the quality of semi-finished and finished wood products before usage. In the case of sawn timber, the evaluation is based on the visual characteristics of wood and wood-based products. There exist certain classification systems to determine the grade of the wood-based products; however, there are still many inconsistencies in this field. The purpose of this thesis is to create a simple algorithm for estimating tensile strength of beech boards. The estimation is based on the visual characteristics of the beech wood. In the first part of the thesis, we briefly describe wood as a material and present its features as well as certain visual characteristics of beech wood that are most likely to influence the mechanical properties and the ultimate tensile strength of wood. In the following chapters, we analyse four different types of fracture on the surface of the board and two types of fracture on the edge of the board. These types of fracture are defined according to our experimental observations. Furthermore, we try to determine which visual characteristics are typical for each type of fracture. On the basis of the results of tensile tests, we try to determine the level of the ultimate tensile strength for each type of fracture or the combination of fractures on the edge and on the surface of the board.