Abstract High field I c performance of commercial high T c superconductors, in view of applications such as an insert magnet for high field generation beyond 20 T, needs to be directly measured as no comprehensive relationships exist with the readily accessible 77 K self-field data. We have constructed and tested the measurement probes for high field beyond 20 T using the facility available at LNCMI-Grenoble, and report here the results of the measurements performed on recent commercial conductors relevant to high field applications.