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Diamonds - What Is a Carat?

3 min read

Diamonds - What Is a Carat?

"Have you ever wondered what the difference was between a carat and a karat? These identical-sounding terms in the world of jewellery have different meanings, but it’s easy to confuse them".

Karat is a measurement of the purity of precious metals. For example, an 18-karat gold band is less pure (meaning it has more of other metals alloyed with the gold) than a 24-karat gold band.

A carat on the other hand is a measurement of weight for diamonds and other gemstones. It quite simply measures how much the gemstone weighs. Here’s what you need to know about carats.


What Is a Carat?

A carat is about one-fifth of a gram, or 0.2 grams, or two hundred milligrams. It is only used to refer to gemstones and pearls. Technically, the full term is a “metric carat”, meaning that (for example) a one-carat diamond should technically be described as weighing one metric carat. This has been the standard unit of measurement for gemstones and pearls since 1907.


Why Carats Matter

Gemstones that are extremely large are also extremely rare. In fact, the larger the gemstone, the rarer it is – and the more expensive. In order to determine the price of a piece of jewelry, knowing the exact weight of a gemstone is very important. This is also a measurement of the piece’s value when it comes to insurance, for example. The larger the gemstone, the more likely it is that the piece will be considered a luxury item, which makes it more value to insurers.

There are other factors that can impact the price and value of a piece of jewelry, of course. For example, gemstones are also measured on a group of facets called the “4 C’s”, which include carat, as well as cut, clarity, and color; (here at Arabel Lebrusan we included the 5th C, the certificate of origin). But carat worth is a very big part of this process for any piece that features a gemstone or a pearl.


what is a carat

Our Foliage Ethical Diamond Platinum Engagement Ring, featuring a 0.4ct Canada Mark diamond. Top to bottom, 0.3ct, 0.4ct, 0.5ct diamond.


How Are Carats Measured

Carats are subdivided into 100 points. The weight of a carat is calculated to the hundredth decimal place, so that the weight can be described in very accurate measurements. So a diamond that weighs 0.25 carats (ct) is a 25-point diamond.

One interesting fact about the world of jewelers is that, while gemstones under a full carat are described in whole terms like that (0.25 carats is a 25-pointer, 0.76 carats is a 76-pointer, etc.), any gemstone that weighs over a full carat is described a little differently. A diamond that weighed 1.08 carats, for example, would simply be described as “one point oh eight carats”.

This is important, however, because even differences at the hundredth decimal place can change the price of a piece. A diamond that weighs 0.99 carats is priced differently than a diamond that weighs 1.00 carats.


Choosing a Carat

Most jewelers prefer a few “magic” carat values – the half-carat, the three-quarter carat, and the full carat. These are the most common gemstones you’ll find in luxury jewelry shops, and that makes it easy to match your budget requirements to a quality gemstone.

If you are looking for an engagement ring, you would like a large stone but you have a limited budget, I would suggest you look for a diamond that is 0.70 carats instead of the popular three-quarter carat (0.75ct); or 0.99 carats instead of the sought-after 1ct diamond.



Arabel Lebrusan
Arabel Lebrusan

Arabel Lebrusan is an artist, designer and pioneer of the ethical jewellery movement, with almost two decades of industry experience behind her. She is a fount of knowledge when it comes to responsible sourcing, sustainable manufacture, and the preservation of traditional craft. Her engaging blog posts range from personal accounts of once-in-a-lifetime sourcing trips to helpful tips for buying and wearing jewellery and opinion pieces on pressing industry matters.