A simple and accurate method is presented to determine the flame temperature and the adiabatic burning velocity of laminar premixed flat flames, using a specially constructed flat flame burner. The heat loss of the flat flame is determined from measurement of the temperature profile of the burner plate. The adiabatic burning velocity is found when the burner plate temperature profile is uniform, implying that the net heat loss of the flame is zero. Several methods are presented to determine the thermal conductivity of the burner plate. The results for methane/air mixtures are compared with experimental data found in the literature and one-dimensional flame calculations, and close agreement is found. The method is particularly useful in providing an accurate reference for other temperature measurement techniques (e.g. spectroscopic laser diagnostics), and to determine adiabatic burning velocities over the entire range of flamm ability