International Annealed Copper Standard

The International Annealed Copper Standard (IACS) is a standard established in 1914 by the United States Department of Commerce. It is an empirically derived standard value for the electrical conductivity of commercially available copper (circa 1914). Copper samples from 14 important refiners and wire manufacturers were analyzed by the U.S. Bureau of Standards. The average resistance of the samples was determined to be 0.15292 ohm at 20°C for a uniform cross section of copper 1 meter in length with a mass of 1 gram. The notation used for this is 0.15292 ohm (meter, gram) at 20°C.