Karát

Karát, in English usually written carat and abbreviated as ct, is a unit of mass used to measure the weight of gemstones, most notably diamonds. One karát equals 0.2 grams (200 milligrams). Each karát can be subdivided into 100 points, allowing precise reporting such as 0.37 ct or 1.10 ct. In grading and pricing, carat weight is a major factor, but it interacts with cut, color, and clarity to determine the overall value.

The concept has historical roots in ancient trade, where carob seeds were used as counterweights because of their relatively uniform size. Today, carats are defined and standardized internationally, with 1 ct exactly equal to 0.2 g and the symbol ct used on certificates and price lists. The carat system applies to most gemstones, though density differences mean equal carat weights can correspond to different physical sizes.

In gold and jewelry terminology, karat (often written kt or K) denotes fineness, or the proportion of gold in an alloy. Pure gold is 24 karat; common alloys include 18K (75% gold) and 14K (58.3% gold). The karat system for purity is separate from carat weight, and mixing the two terms can lead to confusion across languages and markets.

For other gemstones, weight is typically measured in carats just as for diamonds, but size is not the sole indicator of value. The price also depends on the other four Cs—color, clarity, cut, and certificate—along with market demand and provenance.