Carats and Gemstone Grading
Carats and Gemstone Grading

Professional Gemologist Certification Course

Carats and Gemstone Grading

What is a Carat?

In English, carat sounds the same as carrot, but we aren't discussing vegetables. Carat also sounds the same as karat, but that's a measure of the fineness of gold or the ratio of pure gold to alloy metals in a mixture. Karat is abbreviated as “K,” while carat is abbreviated as "ct."

One carat equals 1/5th of a gram or 200 milligrams. You could also phrase that as five carats in a gram. A kilogram is 1,000 grams, or 5,000 carats. (My apologies to those of you on the metric system. To Americans, this sometimes needs to be explained).

Gem weights are occasionally expressed in common fractions like ½ or ¼ carats but are more commonly expressed as decimal fractions. (0.25 carats instead of ¼ carats, for example).

A carat is further divided into units called points. There are 100 points in a carat. So, for example, 25 points, 0.25 carats, and ¼ carats are all the same weight.

Carats, Gem Value, and the Law of Supply and Demand

To understand how carats affect a gemstone's grade, you have to reflect on the law of supply and...


Donald Clark, CSM IMG

The late Donald Clark, CSM founded the International Gem Society in 1998. Donald started in the gem and jewelry industry in 1976. He received his formal gemology training from the Gemological Institute of America (GIA) and the American Society of Gemcutters (ASG). The letters “CSM” after his name stood for Certified Supreme Master Gemcutter, a designation of Wykoff’s ASG which has often been referred to as the doctorate of gem cutting. The American Society of Gemcutters only had 54 people reach this level. Along with dozens of articles for leading trade magazines, Donald authored the book “Modern Faceting, the Easy Way.”


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