This article reviews heat flux measurement devices for high enthalpy flows as used in plasma wind tunnel facilities. Only heat flux gages measuring heat flux on cold copper surfaces are considered. The steady state water-cooled calorimeter, the Gardon gage sensor, slug calorimetry and swept nullpoint calorimetry are described. Based on published data and sensor heritage the various designs in Europe and the US are reviewed and analyzed. The paper ends with some remarks on comparability testing in different facilities.