Gold has always been one of the most valuable and desired metals. However, there is a lot of confusion about the way in which gold is classified and measured. Many different terms mean the same thing, and different abbreviations are used in different parts of the world.

K, k, KT, Kt, kt, CT, and ct are all abbreviations with the same meaning. They represent the word Karats, which is spelled Carats in many places outside of the United States. Karats is the measurement used to describe the purity of the gold. Pure gold is 24 karats. Most gold however, is made up of a mixture of gold and other metals. Therefore the karats will describe how many parts out of 24 are gold. For example 18 karat gold means 18/24 of the object is gold. In Europe, this is often referred to as the "fineness" of the gold, and described with a 3 digit number representing the the ration of gold per 1,000 pieces. Using the fineness system, 18 karat gold is equal to a fineness of 750 (18/24 is equal to 750/1,000).

Pure gold is very soft and easily bent. Therefore it is not usually a good choice for jewelry, which requires more durability. Most gold jewelry is made of gold mixed with various other metals. This is called a gold alloy. The other metals in the alloy can also determine the color of the gold.

Most gold is marked with either the number of karats or the 3 digit fineness number. This mark is often near the clasp of gold jewelry, and is easier to find with a jeweler's loupe or a magnifying glass. Additionally, there are chemical and electronic tests, such as an X-ray fluorescence machine that can determine the karats of a gold object. Many jewelers will have these tests available.

In addition to the various ways of abbreviating karats, there are many other common abbreviations you may find on your gold items such as jewelry. KP or kp means Karat Plum, and it means that the amount of gold in the item is not less than the karats shown. GP, gp, or G.P. all stand for Gold Plated, which means the item is made of a different metal with a thin layer of gold attached to its surface. GF, gf, or G.F. all represent Gold Filled, which is similar to gold plated, except that the gold coating is much thicker. HGE, H.G.E. or hge means Heavy Gold Electroplate, which is also called Vermeil. Vermeil objects are made out of sterling silver coated with 10 karat gold of at least 2.5 microns in thickness.