Whether you're looking for a diamond to mount it on a ring, a jewel or invest, you're certainly wondering :

What is the diamond carat ?

This full article offers all the explanations on the subject :

  1. Definition and explanation of diamonds carat
  2. Evaluation of diamond carat price
  3. Measurement, calculation and equivalence between size and carat weight of diamonds

diamond carat measure

Diamond carat, weight unit used to evaluate the diamond price

Free Bonus : Download our complete guide on Diamond (fr).

You'll discover all you need to know to buy diamonds jewelry online or in store.

engagement ring diamond engagement ring diamond engagement ring diamond

Diamond engagement rings from the Vivalatina Collection

Carat definition for diamonds

One carat corresponds to a weight of 0.2 grams in jewelry.

It's a measure unit more accurate than grams for measuring weight of precious stones, especially diamonds.

Historically, the word carat derives its origin from the Arabic word Qirat, seed of the carob tree which served as a reference of weight during the antiquity to weigh the gems.

Indeed, this tree produces seeds of very constant weight (between 0.185 and 0.205 grams) and served as reference standard in the Arab, Greek and Roman worlds.


The carob, fruit of the carob tree, gives seeds used as standard of measurement during antiquity to evaluate the weight of the gems

Linguistic explanation of the Carat :

It's easy to see that all Western languages ​​have the same Greek / Arabic roots. Carat said :

  • in Ancient Greek: Keration
  • in Arabic: Qirat
  • in Italian: Carato
  • in Spanish: Quilate
  • in English: Carat

Be careful, don't confuse the carat definition used in jewelry for gemstones and that used in jewelry to assess the purity of gold. For the latter, we'll write it "karat".

This article will give you all the useful information about the gold karat.

Diamond carat price

Diamond carat is only one of the 4 criteria (the famous 4Cs, to read here) used to evaluate diamond price..

It's therefore not possible to evaluate the diamond price on its sole weight criterion.

To compare the price of two or more diamonds, one must take into account their quality criteria, or compare diamonds of equal quality.

Diamonds most commonly found in jewelry are H-clarity and SI-clarity diamonds, also known as HSI.

You should know that the price scale of diamonds is not linear. As diamonds of one carat are much rarer than diamonds of 0.5 carats, their price is higher than that of two diamonds of 0.5 carats.

chart diamond carat price

Graph showing the price evolution of a diamond carat HSI according to its weight. This graph is only indicative since it doesn't detail the cut quality and other variable criteria influencing the diamond price. 

It must be understood that in equal quality, the more we look for a big diamond, the more expensive we will pay each carat of this diamond.

Thus, if the carat price is less than 1000 dollars for a 0.25 carat HSI diamond, it is more than 2000 dollars for a HSI diamond of 1 carat and more than 4000 dollars for a HSI diamond of 2 carats.

To have an overview (although gross) of the diamond carat price, I invite you to visit this page which gives you a preview.

table carat price

Table showing in dollars, the value of a diamond carat according to its color and its purity (it misses the cut and other criteria less used)

diamond wedding ring diamond wedding ring diamond wedding ring


How to calculate the carat weight of a diamond ?

We can estimate weight according to the diamond size expressed in millimeters or directly measure the diamond weight.

To do so, it's necessary to use a specific scale, the latter usually have a precision of the order of 0.005 carat, which corresponds to one thousandth of a gram.

For the measurement accuracy, it's therefore necessary to weigh in a closed place without air movements.

You can easily find this kind of carat scales online here for example.

scale diamond carat

Precision scale for weighing diamonds in carat units

Diamond weight expressed in points : 100 points equals 1 carat.

As you know, a 1 carat diamond is relatively big and expensive, so most of the time in jewelry, we work with diamonds of less than one carat weight.

So that to express themselves more easily about small diamonds, jewelers speak of points instead of carat.

  • A 100-point diamond equals a 1-carat diamond.
  • 1 diamond of 60 points equals a diamond of 0.6 carat
  • 1 diamond of 10 points equals a diamond of 0.1 carat
  • 1 diamond of 5 points equals a diamond of 0.05 carat

    calcul carat diamond

    3 mm diameter champagne colored diamond weighing 0.11 carats, or 11 points

    Here is a table of the correspondences between the diamond size in millimeters and its weight in carat expressed in points:

    Round diamond : size conversion in millimeter in carat weight

    Note : diamond weight depends on its diameter (taken into account here) but also on its size (which impacts the height of the diamond and therefore its mass).

    Therefore, if these matches are accurate for small diamonds, the values ​​are only indicative for diamonds from 2.5 millimeters in diameter.

    There will inevitably be differences of a few hundredths / tenths of points (tens of milligrams maximum) between the real diamonds weighed by a certain dimension and the corresponding value displayed in this table.

    size weight conversion

    Table showing the correspondence between the millimeter dimension of a round diamond and its carat weight.

    diamond wedding ring diamond wedding ring diamond wedding ring

    Gold rings and round brilliant cut diamond (photo source)

    Princess Diamond : size conversion in millimeter to carat weight

    Note : The remarks on the correspondence between height and weight expressed in the preceding table also apply to princess cut diamonds.

    conversion size weight princess

    Table showing the correspondence between the millimeter dimension of a princess cut diamond and its carat weight.

    diamond wedding ring

    Gold ring with a princess cut diamond (photo source)


    Free Bonus : Download our complete guide on Diamond (fr).

    You'll discover all you need to know to buy diamonds jewelry online or in store.

    For further :

    August 12, 2019 — Hugo Maherault

    Leave a comment

    Please note: comments must be approved before they are published.