Other ; A method for the quantification of the radiative heat losses in a steady-state thermal conductivity measurement set-up is developed based on the Stefan–Boltzmann radiation law with the assumption of a linear temperature distribution along the specimen. The resulting expression can be applied to any regular-shaped sample with well-defined side surfaces and cross-section. Owing to the quantification of the radiative heat losses the accuracy of the steady-state thermal conductivity measurement method is improved and the measurement range can be extended to higher temperatures. An exemplary application in a commercial device is presented. The results are in an excellent agreement with the independently measured high temperature thermal conductivity.