In this work, a three-parameter Weibull methodology for fracture prediction of brittle and ductile materials is presented. The approach proposed requires previous definition of the failure criterion to be applied. The parameter estimation is achieved for proportionally and non-proportionally increasing stresses. The case of two concurrent failure types is also handled. The resulting primary failure distribution can be expressed as a function of an effective size (length, area or volume) for its subsequent application in practical design of specimens or components using FEM.