Beads of Bali

Overview

Even most people who don't wear or buy gold jewelry have a naive sense that a high karat rating reflects a higher percentage of gold in the piece in question. It is also likely that most people know that the maximum amount of karats possible is 24. We even use the descriptor "24kt gold" to describe things and people of high quality." So just what is a karat?

The karat method is used primarily in the U.S. and Canada to measure the purity of gold. The formula is shown below. In the formula M_g is the amount of gold in a piece, measured in grams. M_m is the total weight of the piece, also measured in grams. Thus, M_g/M_m is the proportion of the piece that is gold (by weight). If you have a 20 gram piece of jewelry that has 15 grams of gold in it, then the proportion of your jewelry that is gold is .75 (75%). This proportion is then standardized to a 0 – 24 scale by multiplying it by 24. Thus, your 75% gold jewelry piece could be described as being 24 x.75 = 18kt gold.

Converting Purity Level to Karats

In the table to the left we have converted purity levels, reflected in percentage gold, to karats. Note that 99.9% gold is considered pure.  Note also that no values are given below 10kt. This is because the Federal Trade Commission considers it to be misleading to use "gold" to describe jewelry that is not composed of at least 10kt of gold.

The Millesimal Fineness System

There is a move toward the millesimal fineness syst

em in which the purity of gold is assessed in terms of "parts per thousand." Thus, 12kt gold would have a millesimal fineness score of 500 (500 parts per 1000, or 50.0%).

"Karat" versus "Carat"

There is some confusion about the proper spelling of karat/carat. Karat, with a K (and abbreviated as kt.) should be used when describing the purity of gold.  Carat, with a C (and abbreviated as ct.) should be used when describing the weight of a precious gem. One carat is 200 milligrams. Thus, if you have a diamond ring set in gold, use the K word to describe the gold setting and the C work to describe the gem.

Having said this, the truth is that Karat and Carat are often used interchangeably, even among people who probably know better.  We don't wish to be snobs, but the Merriam-Webster dictionary does differentiate between Karat and Carat. Under no circumstance should "carrot" be used!