In order to develop the methodology to evaluate the upper shelf energy (USE) for full size Charpy specimens of ferritic steels from miniaturized specimen data, the effects of specimen size and notch dimensions (notch root radius and notch depth) on the USE were studied for high strength ferritic steels with relatively low USE values of 135 and 107 J. The USE for miniaturized specimens, normalized by Bb ² or (Bb)^3/2 (B is the specimen thickness, b is the ligament size), was essentially independent of specimen size and tended to decrease with increasing the elastic stress concentration factor, K_t, but the K_t dependence was not significant. The normalized USE for full size specimens was considerably lower than that for miniaturized specimens. A general relationship was found that allows to determine the USE of full size specimens of ferritic steels directly from miniaturized specimen data.