A carat is a unit of weight used to measure the size of a gemstone such as a diamond. A karat is a measurement indicating the proportion of gold in an alloy out of 24 parts, so 18K gold is 18/24 parts gold. However, the use of carat (in place of karat) to indicate the fineness of gold is also considered acceptable.

Although they have a common origin and are pronounced the same, carat and karat now have different meanings. A carat is a unit of weight in gemstones. A karat is a unit for measuring the purity of gold. Carat is abbreviated as c. or ct., while karat is k. or kt.

Data quality in the electronic patient record has long been described by the acronym CARAT, standing for Complete, Accurate, Relevant, Accessible and Timely.

One carat equals 0.200 grams or 1/5 gram and is subdivided into 100 points. For comparison, in units more familiar in the United States, one carat equals 0.007 ounce avoirdupois.