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MainDiamond size


The most important characteristic of a stone is its weight. When it comes to diamonds, a special unit of measurement is used: the carat, or ct for short. Jewelers use specialized precision scales to determine a gem's weight. The rough characteristics of a gem can also be determined without the help of a scale, using visual examination instead, as a diamond's size and its weight correlates significantly. For help, see the Diamond Size Chart.

Diamond Size Chart — Download PDF

What is the carat of a diamond?

How this term came to be is quite curious. The word "carat" comes from the name of the carob tree's seeds, which were used in ancient times to determine the weight of a diamond. In terms of our units of measurement today, 1 ct is equal to 0.2 grams. All in all there are 100 units on a specialized scale.

The weight of a gem is measured with high precision: up to 0.01 ct. But as already mentioned, it is possible to determine the approximate weight by the size of the stone when it is set on its own. Determining the carat weight for a diamond that is already set in a piece is much more complicated. To estimate the weight, a special formula is used. When it comes to the most popular round cut, this formula is height * diameter * 0.0061. The formula may differ slightly depending on the shape of the stone (the last number varies, and length times width is used instead of diameter). For instance, a heart cut uses height * length * width * 0.0059, while a marquis cut, at a ratio of 2:1, uses height * length * width * 0.058.

Diamond carats and stone prices

Prices for processed diamonds vary depending on a number of characteristics. Here are the main criteria that affect prices:

  • weight and size;
  • color;
  • clarity.

Diamonds of less than 0.01 ct (the margin of error in weighing) are considered to be bort diamonds. Other diamonds get divided up into size categories such as small (less than 0.29 ct), medium (0.3-0.99 ct) and large (1 ct and up). Diamonds of different sizes are valued differently. With large stones, more attention is placed on their clarity and color. In smaller stones, these characteristics are hardly noticeable, so weight comes first. Tavernier's law is used to determine the price of a diamond: the value of a diamond is equal to carat weight squared multiplied by the basic price of a 1 ct stone.