The natural material wood is commonly graded with regard to the parallel to the grain strength and stiffness properties and taking into account different growth characteristics such as knots and grain deviations. In this paper the impact of knots and grain deviations on the fracture perpendicular to the grain of timber is analysed by means of numerical models. The results are used for the calibration of an analytical model. With this model it is possible to evaluate the impact of growth characteristics on the perpendicular to the grain fracture and compare the results with test data from literature. The evaluation shows that certain growth characteristics increase the strength perpendicular to the grain. This is in contrast with current grading procedures, where such growth characteristics are considered as being strength decreasing. The results are compared with a model for the description of the effects of growth characteristics on the distribution characteristics of the strength perpendicular to the grain. This strongest link model can be used to describe phenomena with a parallel system of failure events.