The weight of a diamond is expressed in fractions or multiples of a carat, to work this into a more familiar measurement that you can understand one carat is equal to 200 milligrams. The word carat came to the English language from French, derived from the Greek keration, “fruit of the carob”. This is because in past centuries, different countries each had their own carat unit, but all were roughly equivalent to the mass of a carob seed. These units were also often used for weighing gold.
Obviously carob seeds are not a measurement that could be accepted today, which lead to the modern definition of the weight of a carat which has been standardized to be equal to exactly 200 milligrams. This measurement is known as the metric carat, and it was adopted universally from 1907. This ‘metric carat’ is the measurement used for all diamonds you can buy today. The metric carat can be further split into 100 grains of 2 milligrams each. It is interesting to note that in the far east where the carob seed doesn’t grow the ancient measurement of a diamond was based on a grain of rice, and expressed in grains , four of these grains being equal to one carat, however this measurement is no longer used.
When buying diamonds or jewelery containing diamonds there are a few points to remember. If the stones are already set or mounted in the piece of jewelry, or the piece has more than one stone, the weight will be quoted as the CTW, or carat total weight. Be aware that this is not the carat weight of each stone, but the carat weight of each stone added together, and it is often easier to get a much clearer understanding of what you are buying to ask the jeweler what the carat weight of the largest individual stone in the piece is.
By far the most popular weight of stone found in modern retail diamond jewelery is usually one third of a carat, and this is what the vast majority of diamond engagement rings contain.
There are many points to consider when buying a diamond, and it helps to truly know the terms and secrets of the diamond and jewelery trade before you make that purchase. Make sure you fully understand what you are buying, before you part with your cash.