Fineness of gold (karat value) Since ancient times the purity of gold has been defined by the term karat, which is 1/24 part of pure gold by weight. Pure gold is equivalent to 24K. Gold purity may also be described by its fineness, which is the amount of pure gold in parts per 1000. For Federal Trade Commission rules require that all jewelry items sold in the United States as gold shall be described by a correct designation of the karat fineness of the alloy. No jewelry item less than 10K may be sold in the United States as gold jewelry. The following table lists the relationship between different international gold markings.