Failure of mechanical structures may be caused by presence of some defects like cracks. These defects are generally created due to manufacturing processes or in-service applications. Failures due to cleavage fracture usually lead to catastrophic effects, thus studies of such failures are important. Main approaches for fracture assessment of structures are global approach (classical fracture mechanics) and local approach. In the previously presented models of local approach, unknown parameters are introduced which have to be calibrated using experimental fracture data. Despite of existing different calibration methods, obtaining suitable parameters for predicting brittle fracture based on local approach, has been limited in some cases. The purpose of this study is presenting a rational method for predicting brittle fracture in specimens of different shapes to transform it into full scale cases. In this paper, by considering the location parameter of Weibull distribution as a stress triaxiality criteria and modifying the Beremin model, predicting brittle fracture in specimens of different shapes are studied. Also, independence of the parameters from their shapes is shown and eventually a linear relation between location parameter of Weibull distribution and triaxiality factor for the material is presented.