One of the most
important aspects of a diamond is its weight. When someone asks you about a diamond, the first thing they
will ask is how big is it. And you will probably respond with its carat weight, not its mm size.
This lesson will help you understand how diamonds are measured and the terminology used to describe it.
For centuries, diamonds have been measured by weight to determine its value.
This was done as far back as 500bce in the Middle East. In 1907, at the Fourth General Conference on Weights
and Measures, the metric carat was adopted standardizing this measurement. Currently a carat is defined as
exactly 200mg (0.007,055oz, 3.086 grains). A carat is further divided into 100 points. One point
equaling 0.01ct, 1% of one carat or 2mg.
For example, 0.75 ct. = 75 points, 0.50 ct. = 50 points. The bigger the
diamond, the more it weighs, the higher its carat weight.
The following chart shows the approximate diameter of a round brilliant diamond compared to its carat weight.
A few famous diamonds included for comparison.
Carats
Example
Size
0.10ct
3.00mm
0.25ct
4.10mm
0.50ct
5.20mm
0.75ct
5.90mm
1.00ct
6.50mm
1.50ct
7.40mm
2.00ct
8.20mm
2.50ct
9.00mm
3.00ct
9.30mm
5.00ct
11.00mm
10.00ct
14.00mm
15.00ct
16.30mm
27.64ct
Heart of Eternity
19.99mm H 20.01mm W 11.89mm D
45.52ct
The Hope Diamond
25.60mm H 21.78mm W 12.00mm D
530.20ct
Cullinan I a.k.a. The Star of Africa
54mm H 44mm W 29mm D
1 Inch
1 cm
1 mm
How Carat Weight Affects Value
Larger diamonds are rarer
and in more demand than smaller
diamonds of the same quality, so
they can be sold for a higher
price. A one carat diamond
solitaire ring is nearly always
more expensive than a diamond
ring made up of multiple
diamonds that are similar, but
smaller, even though they total
one carat or more.
Diamonds that weigh just under
the next full carat are
typically less expensive than
diamonds passing the full-carat
hurdle. The Hope Diamond is a 45.52 carat diamond valued up to $250 million. And at 530.20 carats, the Cullinan I or The Star of Africa is the largest cut diamond in the world
and is valued at about $400 million.
