Optical diagnostic thermometry techniques are not generally traceable to temperature standards and due to their complexity it is often difficult to assess their absolute accuracy. This work aims to address this by calibrating a McKenna premixed flat-flame burner with a high-accuracy Rayleigh scattering thermometry system. By applying corrections for the temperature dependence of the scattering cross section, it has been possible to determine the temperature of a premixed propane/air flame with an uncertainty of less than 1%. The temperature dependence of the differential Rayleigh scattering cross section arises from changes in the mean molecular polarizability and mean molecular anisotropy. Changes in the cross section of up to 2% between room and flame temperatures have been found. The burner and associated gas mixing system are described here as a combustion temperature and species standard allowing the calibration of optical diagnostic techniques. (c) 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.