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In geology and the jewelry industry, the terms “carat” and “karat” are used quite frequently. Though they sound the same and are often used interchangeably, the words “karat” and “carat” refer to different things. Keep reading to learn more about the difference between these two easily confused terms.


Karat is used when referring to gold. When gold is described, there are three common specifications included. These are the dimensions, the weight in troy ounces, and the gold fineness. Fineness, also known as purity, is the ration of the weight of the gold to the base metals or impurities. This can be expressed in a number of ways including parts per 1,000, decimal points (0.999 pure gold), percentage (99.9% pure gold), and karats. Many places that buy gold and silver in Atlanta measure the purity of their products using karats. The karat system is measured on a scale of 24 where one karat means 1/24 of the product is gold. The karats of an item can be determined by multiplying the mass of the pure gold in the item by 24 and dividing that number by the total mass of the object. So, an item that is 18 parts gold and 6 parts base metals is called 18-karat and so on. An item that measures 24 karats is referred to as pure gold.


Carat is used when talking about the mass of diamonds and other gemstones. One carat is equal to 200 milligrams. Before 1907, different countries had their own standards for what one carat was equal to. At the Fourth General Conference on Weights and Measures in 1907, the system was standardized and the current carat measure was first put into place. So, for American English, remember karat is used when talking about gold and carat is used when talking about gemstones.


As stated by the Online Etymology Dictionary, “karats” used as a measure of gold purity has been around for longer than “carats” as a measure of gemstone weight. The word “karat” traces its origins to the mid-15thcentury from the Arabic word “qirat” which means the fruit of the carob tree and a weight of 4 grains. It can also be traced back to the Greek word “keration” which means a carob seed and a small unit of weight. At this time, carob beans were often used as a measure of weight in small quantities. The keration was the equivalent of the Roman siliqua, which was equal to 1/24 of a gold solidus of the emperor Constantine. Karat became to mean a portion of 1/24 and was first used as a measure of gold purity in the 1550s. On the other hand, “carat” was not used as a means of measuring the weight of gemstones until it emerged in English in the 1570s.