Karat

Karat (abbreviated to kt or ct) is used to measure the purity of gold. It uses a scale of 24, where 24 karat means pure gold.

Measuring Karat Purity

To measure karat purity in a given material, we can use the following equation:

X = 24 (Mg/Mm), where

X = the karat rating
Mg = the mass of pure gold in a given material
Mm = the mass of a given material

24 karat therefore means pure gold, 18 karat means 75% gold and so on.

To measure the purity of gold, we can also use the millesimal fineness system. In this system, purity of gold is denoted by parts per thousand.

The most commonly used karats are as follows:

  • 24-karat (millesimal fineness 999 or higher)
  • 22-karat (millesimal fineness 916)
  • 21-karat (millesimal fineness 875)
  • 20-karat (millesimal fineness 833)
  • 18-karat (millesimal fineness 750)
  • 15-karat (millesimal fineness 625)
  • 14-karat (millesimal fineness 585)
  • 10-karat (millesimal fineness 417)
  • 9-karat (millesimal fineness 375)
  • 8-karat (millesimal fineness 333)
  • 1-karat (millesimal fineness 042)

In the UK, karat was also divided into four grains, and the grain was divided into four quarts. A gold alloy of 381/384 fineness (99.2% purity) could also be described as 23-karat, 3-grain, 1-quart gold.

Where does the name "karat" come from?

The word karat comes from the Greek word kerátion (κεράτιoν), which means “fruit of the carob”. Carob seeds are known for their uniform weight. That is why in the past they were used to measure things where precision was needed. Carob is also called St. John’s bread, because its pods are thought to have been eaten by John the Baptist in the wilderness.

In the very distant past, different countries used to have different “karats”, all of which were roughly equivalent to the weight of a carob seed. Karat was adopted as a universal measure of gold purity in the mid 16th century.

Typical Karatage around the world

Country/Region

Karatage (Fineness)

Arabic Countries, Far East

24-karat "Chuk Kam" (99.0% min)

Arabic Countries, Bangladesh, India, Pakistan, Sri Lanka

22-karat (91.6%)

Persian Gulf Countries

21-karat (87.5%), 18-karat (75.0%) in most of Egypt

Southern Europe/Portugal

19.2-karat (80.0%)

Southern Europe/Mediterranean

18-karat (75.0%)

Northern Europe/Germany

8- to 18-karat (33.3 - 75.0%)

Russia/Former USSR

9- (37.5%) and 14-karat/old 583

United Kingdom

9-karat to 22 karat (37.5-91.6%)

United States

10-karat to 18-karat (41.7-75%)