The weight of a diamonds is generally given in carats. The term
carat originated in ancient times when gemstones were weighted against the carob
bean. Each bean weighed about one carat. In 1913, carat weight was standardized
internationally and adapted to the metric system. One carat equals 0.2 grams -
a little more than 0.007 ounce. In other words, it takes 142 carats to equal 1
Two terms, carat and karat are often confused. Karat refers to the
fineness of gold alloys (pure gold is 24 karat; 14 karat is 14 parts gold and
10 parts other metals) and carat refers to gem weights.
The weight of
small diamonds is frequently expressed in points, with one point equaling 0.01
carats. For example, five points is a short way of saying 5/100 of a carat and
fifty points equates to a half carat.
Sometimes in the jewellery trade,
the term size is used as a synonym for carat weight. This is because small round
diamonds having the same weight also look the same size and similar diameters.
As diamonds increase in weight, their size becomes less predictable. Diamonds
with a shallow cut can have a greater diameter than a deeper cut diamond with
the same weight. However, you don't want the diamond to be too shallow or it will
not reflect the light properly and will have less brilliance.
It is similar to asking how tall a 200 pound man is. You
have no way of knowing because you don't know how the man is proportioned. The
same holds true for diamonds. So if size is important to you, focus on diamond
measurements as opposed to carat weight. You don't need to carry a millimeter
gauge when you go shopping. Just start asking what the different millimeter measurements
are and note how they look. Diamonds that look big for their weight may have reduced
brilliance and fire so always insist on great cut.
Note that an increase
in carat weight does not produce the same increase in millimeter diameter. For
example, there is a 25% increase in carat weight from 1.00 carats to 1.25 carats
but less than 8% increase in diameter (6.5 to 7.0 mm). This concept, along with
the increased price per carat, explains why prices increase dramatically in order
to get noticeably bigger millimeter size. Please have a look at the figure below
to see the carat weight of a diamond and diamater in mm.
The weight of a diamond has a large impact on price. All other
factors being equal, the heavier the diamond, the greater its cost will be. Diamonds
lose approximately 40-60% of their rough weight when they are cut. Over 1 million
rough diamonds must be mined before one is found that can be cut into a 1.00 carat
finished diamond! Please have a look at the figure below to get an impression
of price increasement based on carat. Have a look at our Diamond
Education - Cost page to learn more about cost on diamonds.
With each weight category increase (quarter, third, half), the value per carat
of a diamond will increase significantly and almost geometrically (given all have
the same other factors). A stone which is twice as large as an otherwise identical
smaller stone might be three or more times more expensive. So while you might
see a price for a smaller stone at $2,000 per carat, as you price the same cut,
colour and clarity in a larger stone you'll see dramatic increases.
are standards for reporting a diamond's weight. FTC guidelines allow a one-half
point (1/2) tolerance in the stated weight of a diamond. For example, a diamond
weighing .495 carat can be legally sold as a 50 point diamond, while a .494 carat
diamond must be sold as a 49 point stone. Some stores sell diamonds according
to size ranges so you need to insist on knowing the exact weight of your loose
Advice: Look for diamonds that
have a diameter measurement that is at least as large as the average for that
weight. In other words, don't pay for weight you can't see.
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