Carat and karat are different.
A carat is the the unit of weight for diamonds and other precious stones.
A karat is the measurement of the purity of gold.
A carat is the standard unit of weight for diamonds and most other precious stones. One carat is the equivalent of .20 (-1/5th) of a gram or 200 milligrams. For smaller diamonds, you might see weight expressed as “points,” with one point equaling 1/100 of a carat. 100 points = 1 carat (1.00ct). Often when people speak about the weight of a diamond, they often use the term size.
The Black by Brian Gavin® Approach to Carat
To capture the height of beauty from your diamond, it’s important to consider not just carat alone, but rather as well as the overall craft of the stone overall. A well-cut and beautifully polished diamond with precise symmetry and proportions will have more fire and more brilliance, and give the overall impression that it is larger than a stone of equal weight with imprecise proportions and a lesser cut . Diamond weight isn’t everything. What people notice most and what increases a diamond’s wow factor is the way it transmits light back to the viewer’s eye—which is affected more by cut than any other factor.
In the U.S., the average diamond engagement ring sold today has a weight of about ¾ ct.