GIA's pictorial example of carat weight

GIA’s pictorial example of carat weight

GIA's carat weight pictorial diagram

GIA’s carat weight pictorial diagram

Materials and images kindly provided by the Gemological Institute of America – GIA
Click images for larger view

Diamonds and other gemstones are weighed in metric carats: one carat is equal to 0.2 grams, about the same weight as a paperclip.

Because even a fraction of a carat can make a considerable difference in cost, precision is crucial. In the diamond industry, weight is often measured to the hundred thousandths of a carat, and rounded to a  hundredth of a carat.