A new methodology is proposed to correlate the upper shelf energy (USE) of full size and subsize Charpy specimens of a nuclear reactor pressure vessel plate material, A533B. The methodology appears to be more satisfactory than the methodologies proposed earlier. USE of a notched-only specimen is partitioned into macro-crack initiation and crack propagation energies. USE of a precracked specimen provides the crack propagation energy. AUSE, the difference between the USE of notched-only and precracked specimens, is an estimate of the crack initiation energy. AUSE was normalized by a factor involving the dimensions of the Charpy specimen and the plastic stress concentration factor at the notch root. The normalized values of AUSE were found to be invariant with specimen size.