A novel methodology for extrapolation of the performance of ITER class machines is introduced. This procedure utilizes the ITER ELMy H mode database by means of a similarity approach where every discharge is extrapolated to a machine satisfying the ITER performance requirements through the use of the tokamak system code developed during the course of the ITER design evolution. This approach attempts, amongst other things, to overcome the difficulty associated with the simultaneous choice of non-dimensional parameters which, in particular when close to their respective limits, may have some significant mutual interactions affecting energy confinement time. The methodology is also applied to the ITER Physics Basis scalings to develop a non-statistical approach where fusion power is extrapolated at constant beta and confinement is assumed to follow a gyroBohm form. In both cases, out of more than a thousand discharges in the ELMy H mode database, less than half turn out to extrapolate to a Q = 10 machine whose major radius is smaller than 8 m. However, a significant number of discharges do extrapolate to a Q = 10 machine with R<6.2 m. This strengthens confidence in the present choice of ITER parameters. In addition, from this analysis, it has been possible to identify a set of high performance `ITER relevant' discharges from a number of machines, which could be used as starting points for investigation of further improvements in confinement.