CT – disambiguation, indicating a measure of weight, equal to 200 milligrams, or 0.2 g. Often in carats to measure precious stones and gold. The word carat is of Arab origin ("kirata") and originally meant the pod of the carob tree, whose seeds, in ancient times was used as a measure of mass.

Carat as a unit of measurement samples

The British carat – unit of measurement of the percentage of gold in jewelry, bullion, coins, equal to 1/24 the mass of pure substance present in the total mass. As a rule, is used for marking purity of gold and is denoted by a capital Latin letter K. as an example: 583-I test corresponds to a 14KT gold, 375-I – 9K. The purest gold is 24K.
The seeds of the carob tree are homogeneous and have the same weight, and therefore became the unit of measurement.

Good to know that gold is soft and very often combined with the so-called "filler metals" (such as: silver, copper, Nickel). White gold, the shade obtained by adding silver, palladium or platinum, will have more carats than the one that fused with Nickel.

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To measure the mass of gemstones and pearls used metric carats. It was installed the 4th General conference on weights and measures in 1907 and came to the Soviet Union in 1922. Unlike the British, it is abbreviated as "ct" (in Russian language – "CAW"). The abbreviation "ct TW" means total weight of multiple diamonds in jewelry.
The scale of measurement carat is divided into one hundred units, so the gemstones can be measured with an accuracy of up to 0.01 carats.

It should be noted that different stones of the same weight will not necessarily have the same size, because some of them have different density. So, two diamonds of the same carat weight can cost differently, depending on such additional factors as cut, clarity, color. But in General, the larger the carat, the higher the price – the large diamonds are quite rare.

In order to calculate the volume of a standard round diamond, mounted in jewelry, apply the formula M=(D^2) x H x 0,0061, where D – diameter, H – height, M – mass in carats.

There is another way: the approximate weight of a diamond can be calculated by the table diameter ratio and CT.