The design requirements of the aerospace and high temperature nuclear reactor industries necessitate reliable thermal expansion data for graphite and other carbonaceous materials. Currently there are no accepted standards or reference materials which can be used in carbon‐rich atmospheres at temperatures ranging to 2500°C. The feasibility of an acceptable reference for calibration of expansion measuring systems that operate in such test environments (furnaces utilizing graphite heaters, for example) is the prime subject of this work. Present‐day graphite technology provides acceptable materials for stable, reproducible references, as reflected by some of the candidate materials. The repeatability for a single specimen in a given expansion measuring system was found to be± 1%, while the combined results of several tests made on a number of samples fell withina ± 2.5%band. Data on several grades of candidate graphites are discussed, and results of a broad round robin program presented.