Carat is the unit of measurement and expresses the weight of the gemstones. One carat is 200 mg and 5 carats equals 1 g. Carat is further divided into points. One carat is 100 points. For example, 0.67 carat is equal to 67 points. A fraction also expresses units smaller than a carat, like 2/3 carat.
Please do not confuse ‘carat’ with ‘karat’. Karat measures gold purity and is 1/24th. Thus, 18 Karat gold is 18/24 which is 75% pure. In the United Kingdom, ‘carat’ weight and gold ‘carat’ purity are both spelled with a ‘c’.
The carat weight is the weight of a single diamond. The total carat weight is the combined carat weight of all the diamonds or gems of a piece of jewelry. If a piece of jewelry has 3 diamonds each 1/3 carat, the total carat weight is 1 carat.
The most common abbreviation for the total carat weight is “ctw” (or “CTW”). It is also abbreviated as TW, and “dtw” (or “DTW” for “diamond total weight”).
The actual weight of the diamond you buy may be more or less than the fractional weight specified. The Federal Trade Commission has strict guidelines on the allowed range of carat weight that a fraction can represent.
The following table shows the acceptable range for the fractional representation of carat weight.
|Fractional Carat Weight||Allowed range of Carat Weight|
|1/4||0.21 to 0.29|
|1/3||0.30 to 0.36|
|1/2||0.45 to 0.59|
|3/4||0.70 to 0.84|
|1||0.95 to 1.10|
|1 1/4||1.20 to 1.29|
|1 1/2||1.45 to 1.55|
|2||1.95 to 2.05|
Why is carat weight important?
The carat weight of a gemstone is one of the major factors which defines the price. But there are other important factors too. Like cut, color, and clarity.
Larger gems are rarer compared to smaller ones. The price of a 2-carat gem is much higher than two 1-carat gems of the same quality.
Carat could be used to compare the size of the gems of the same type (e.g. a 2-carat diamond is twice the size of a 1-carat diamond). But, when comparing gems of a different type, carat may not be a good indicator of their sizes. For example, a 1-carat sapphire would be smaller than a 1-carat emerald. Because sapphires are denser than emeralds.