Jewelry Glossary

Unit of weight used to measure precious stones and diamonds. Abbreviated "ct" or "c." One carat is equivalent to 1/5 of a gram. A hundredth of a carat is also called a point. Thus a .10 carat stone can be called either 10 points, or 1/10 of a carat. A one carat round diamond is approximately 6.5mm in diameter. This relationship of weight and size is different for each type of gem stone. For example, rubies and sapphires are both heavier than diamond, so a 1 carat ruby or sapphire is smaller in size than a carat diamond. (Karat with a "K" is a measure of the purity of a gold alloy.)

See also: Carat total weight (ct. tw.)  Karat  Four C's