Total heat flux gauges are widely employed in fire research and fire testing laboratories. Several fire laboratories have developed systems for calibrating these gauges. There are major differences between these calibration facilities, and prior to this work there had been no systematic check of the degree of agreement between calibrations from the different laboratories. This report describes the results of two round robins in which five fire laboratories performed independent calibrations of two sets of Gardon and Schmidt-Boelter total heat flux gauges (i.e., a total of four gauges). One set of the gauges was also calibrated by two additional laboratories whose primary focus is measurement and calibration. Even though systematic variations between calibrations from the different laboratories were identified, the degree of agreement is viewed as being satisfactory for most fire testing and research purposes. Additional experimental findings concerning gauge angular response and linearity are presented. The need to develop a better understanding of the relative response of this type of gauge to radiative and convective heat transfer is emphasized.