Carat weight

What you need to know about the weight of a carat - Lorenz Bäumer

What is a carat?

The unit of measurement used to weigh a stone
in the world of jewelry is the carat. The weight of the stone,
as well as its quality, are among the precise criteria used to determine
its retail price in jewelry, especially for
diamonds.

The method for weighing and measuring the weight of a carat

This weight is measured during the diamond's weighing using a specific unit of mass unique to gemstones: the carat. Adopted in 1907 at the 4th General Conference on Weights and Measures, the metric carat is equivalent to 200 milligrams, or 0.20 grams. To ensure a quality criterion and absolute millimeter precision, weighing is carried out to the hundredth or even thousandth of a unit. One carat is therefore divided into 100 points; thus, "25 points" refers to a quarter of a carat, which is equivalent to 50 milligrams, or 0.05 grams. In French, the unit is generally abbreviated as "ct", but in the world of jewelry, the carat as we are discussing it should not be confused with the one that denotes the purity of gold: "K" or "kt", for "karat" in English. Thus, 1 carat is equivalent to 0.20 grams, and 0.1 carat is equivalent to 0.02 grams.

 

The tables below illustrate the correspondence between the diameter of a brilliant-cut diamond and its carat weight.

Visualize the relationship between diamond carats and diameters using these tables.

Table illustrating the millimetric correspondence of the diameter of a diamond and its weight
in carats.

Table illustrating the correspondence between a diamond's diameter and its weight in carats.

The table below illustrates the exponential evolution of a diamond's price per carat.

The origin of the carat

The French word "carat" as such comes etymologically from the Arabic word "kharoûb", or carob in French. This refers to
the seeds of an African tree: carob seeds. According to
historical research, these seeds were indeed long used as millimeter-sized counterweights in scales and thus served as a guide mass unit for weighing diamonds. However, one should not confuse the carat that determines the weight of gemstones and is commonly used in sales, with the
carat that determines the fineness of metals such as gold. Whether you are a jewelry enthusiast, a jewelry lover, or planning a future engagement, knowing the meaning of carat will certainly be useful in your search for the ideal diamond and the jewelry of your dreams, for a successful engagement.

The influence of the carat in the choice of a gem

The value and quality of gemstones are determined by many criteria such as color, cut, clarity, and weight (carat). These are the 4Cs, specified on the GIA certificate, and are closely related guides for determining jewelry value.
However, it is true that it is primarily the weight of a stone that exponentially determines its price. Large precious stones are rare, and therefore give great value to the stone, even though a proportional relationship between mass and price is not officially established. It is therefore vital to take the most precise metric measurement during a sale, which will be indicated on the GIA certificate, in order to correctly determine both the mass (carat) and the price of the stone and the piece of jewelry.

The subtleties related to the weight of the carat

To measure a stone's carat, you need to use a special scale, taking a few precautions. This scale will only be accurate if it is protected from heat sources, drafts, or vibrations. Furthermore, generally speaking, a gemstone's weight depends on its shape. For example, a 2 mm round diamond weighs 0.03 carats, while a 2 x 2 mm square diamond weighs 0.05 carats.

It is also worth noting that this relationship between shape and carat varies from one stone to another: for example, a 2 mm round sapphire weighs 0.04 mm, whereas an emerald of the same size will only weigh 0.03 carats. This is due to the differences in density of each stone. Whatever gemstone you choose, keep in mind that the larger the size, the more carats there are, and the higher the price.

Moreover, for the same weight, stones with high density will be smaller than stones with a lower density. Thus, for the same carat weight, sapphires will be smaller than diamonds, because sapphire has a higher density. On the other hand, a tourmaline weighing 5 carats may be larger than you envisioned, and this is because tourmaline has a fairly low density. The weight-to-size ratio of a stone is thus directly linked to its density. To illustrate, the density of ruby is 3.97 to 4.05; that of tanzanite is 3.35. Thus, ruby has a higher density and will be, for the same weight, smaller than tanzanite.

Weighing of diamonds on a jeweler's scale (in grams).

How to choose the weight of a diamond?

When looking at a diamond, the first thing one sees is its cut, its geometric shape (round, oval, pear, heart, etc...). But its weight is not visible to the naked eye; what one sees is its volume, its dimensions. Therefore, when searching for the ideal stone, it is worth considering visible criteria such as the stone's dimensions, its clarity, its certificate... before looking at the carat.

Colorless diamonds or colored diamonds, precious stones or not, rubies, sapphires, tanzanites... Whether for setting rings, wedding bands, earrings, necklaces... For an engagement or to expand your jewelry collection... in all cases, you will need to know what a carat means when purchasing a gemstone or piece of jewelry, such as for acquiring rings or earrings.

In summary, when searching for the ideal wedding band, rings, or earrings, it is important to first focus on visual criteria before looking at the carat: precious or non-precious stones, colored or colorless, their dimensions... While also considering their clarity and GIA certificate. Whether you are looking for the ideal high-clarity diamond for your future wedding band or simply to expand your collection, the choice of carat weight will come later; it is the finishing touch.

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