The term Carat or Karat (United States), is not to be confused with the unit used to measure the weight of gems. The term originated from the German gold coin called a 'mark' which was common in the 19th century. It weighed 24 carats, the same measurement used to weigh gems. Since they could not be produced in pure gold due to the metal being too soft, other metals were added, such as copper, to harden the coin. This then resulted in the term carat representing the percentage of its carat weight made up of pure Gold.

How is Gold Carat calculated?

1 gold Carat is 1/24 part, or 4.1667 % of the whole metal, of pure gold. For example a 22 Carat Gold Coin is made up 22 parts of pure Gold and 2 parts of another metal (forming an alloy with 91.6 % of pure gold). Hence Carats are expressed as the number of these parts of pure Gold it comprises. See chart below.

How else is the purity of Gold Measured?

The Carat or Karat is a measurement mainly used in the United Kingdom or United States respectively. However many European countries, as well as the four Assay offices in the UK, when hallmarking use the millesimal fineness system for standardisation. This system is represented by the purity of Gold, Platinum and Silver alloys by parts per thousand of pure metal by mass in the alloy. For example an alloy containing 91.6% of Gold is shown as "916" and is usually rounded to a three digit number, particularly when used as a hallmark.