The problem of fracture toughness transferability is treated by using the stress triaxiality and by introduction of a new transferability parameter called p. This parameter is a combination of effective critical stress triaxiality (mean value of stress triaxiality over effective distance) and multiplies by a geometrical function. Application of this method has been made on three point bending specimens made in XC 38 steel. Comparison of 2D and 3D approaches is made.