Diamond Carat - The Unit to measure weight of Diamond

Diamond Carat - It's not about diamond purity, it's the unit to measure weight of diamond.

In jewelry world, the terms Carat and Karat are widely used. While Carat (Ct) is used as the unit to measure weight of diamond, Karat (Kt) is used as unit to evaluate purity of gold.

However, many people are often confused between these two terms, and frequently associate "carat" with purity of diamond, which is not correct.

Actually speaking, I have come across so many people who unknowingly use these terms interchangeably without really knowing the difference between these terms.

Origin of term "Carat"

The word "Carat" is derived from Carob tree. In ancient times, gem traders used small uniform seeds of the fruits from this tree as counter-balance for weighing gems.

Carat term in different languages

Diamond Carat (Weight of Diamond)

Carat is the unit of measurement of diamond weight and not size. It’s used as a measurement of weight for faceted precious stones like diamond and other transparent semi-precious stone. Since 1913, most countries have accepted 1 metric ct. as 200 mg, or 1/5th of gram.

The ct is subdivided into tenth, hundredth and even into thousandth. Very small diamonds are measured in Points. Carat is also subdivided in Grain, a unit of measurement for weighing pearls.

It has to be noted that the carat weight does not refer to exactly one figure. It comprises of stones within a certain weight range (examples shown in below table). This holds true for all carat weight figures.

Diamond Carat Weight Range

Apart from factors like cut, color and clarity, diamond carat is an important factor in determining its value. You may read how the carat weight affects the price of diamond and classification of diamond according to size.

Karat (Purity of Gold)

Karat denotes the percentage of pure gold in the given piece of gold. In other words, the karat mark (abbreviated as K or Kt) indicates the quality or purity of gold, with pure gold bench-marked as 24 kt. Let me explain by example.

Imagine there is a piece of 100 g of pure gold. Since it’s pure gold, it will be 24 Kt. Now, suppose if 10 g of this pure gold is replaced by some impurity (or other metal) of equal weight, then the resulting metal will have 90 g of pure gold and remaining 10 g of impurity. So, on the karat scale, purity of resulting gold will be 21.6 Kt (i.e. 90/100 * 24).

Formula for calculating purity (Karat) of gold

Frequently Asked Questions

  • How many carats is pure diamond? With this question, questioners assume that diamond carat is associated with purity of diamond, that's why ask this question. However, the appropriate question should be "how many karats is pure gold?". This is because there is no direct relationship between carat (weight) of diamond and its purity. After all, carat of diamond will depend on its actual weight, and not on its purity.
  • What is the karat weight of pure gold? Here questioners assume there is some relationship between 'karat weight' and purity of gold. In fact, the right question should be "how many karats is pure gold?", and answer is 24 karat. Note that I have removed the word "weight" from original question.
  • What is karat used to measure? Karat is used for measuring purity of gold.
  • How to check purity of diamond? The term "purity" is usually not associated with diamond. Generally, it is related with gold, i.e. the measure of extent to which gold is mixed with other metals. In case of diamond, it's about "clarity" and "color". Clarity is the extent of flaws (internal and external) the diamond has, and color of diamond tells if it has traces of other elements (like - nitrogen, boron etc.) apart from carbon.

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