Carat: The First of the 4Cs – the Foundation of Sparkle
What do a carob tree, a parcel from South Africa and your engagement ring have in common? The word “carat”. Carat is the first of the famous 4Cs and the only one you can simply measure on a diamond: its weight. Here is why it still doesn’t decide a diamond’s value on its own.
- One carat (ct) weighs exactly 0.2 grams and is divided into 100 “points”.
- The name comes from the carob tree: Greek kerátion, Arabic qīrāṭ.
- Carat measures weight, not size. Value is set by all 4Cs together: carat, colour, clarity and cut.
- For diamonds, carat means weight; for gold, karat means purity. 18-karat gold is 750/1000 pure gold.
What is a carat?
The carat (ct) is the unit of weight for diamonds and gemstones. One metric carat equals exactly 200 milligrams, or 0.2 grams. Five carats make one gram.
Each carat is divided into 100 points of 2 mg each. A diamond of 50 points weighs 0.50 ct; a 0.25 ct stone is known in the trade as a “twenty-five pointer”. So a 0.75 ct diamond weighs 150 milligrams.
Where does the word come from?
The term goes back via Italian carato and Arabic qīrāṭ to the Greek kerátion, the seed of the carob tree (Ceratonia siliqua). Traders are said to have used the seeds as counterweights on their scales.
The 200 mg metric carat only dates back to 1907. Before that, a carat weighed different amounts depending on the trading centre – from around 187 mg in Cyprus to 215.99 mg in Livorno. Anyone selling diamonds between two ports had to be good at maths.
Carat is weight, not size
Two diamonds with identical carat weight can look different in size. How much surface a stone shows from above and how much it sparkles depends mainly on the cut. So carat is the foundation – but only the interplay of all 4Cs (carat, colour, clarity, cut) determines beauty and value.
If everything else is equal, the heavier stone is rarer and usually more expensive. Prices don’t rise in a straight line, though: the larger the diamond, the more each individual carat usually costs.
According to GIA, there are so-called “magic sizes” such as 1.00, 1.50 and 2.00 ct. A 0.99 ct stone is almost impossible to tell apart from a 1.00 ct stone with the naked eye, yet the price difference can be significant.
One stone or many: what “ct” on the label means
For jewellery with several stones, the total weight is usually given. Our Ring 1AP18G in 18-karat yellow gold, for example, carries 26 brilliants with a combined 0.27 ct. The GIA Premium tennis bracelet has 35 brilliants totalling 17.65 ct – and every single stone comes with its own GIA certificate.
Carat or karat?
In German one word, “Karat”, covers two things; English at least spells them differently. For diamonds, carat measures weight; for gold, karat measures purity. 24 karat is pure gold, 18 karat means 18 parts out of 24, i.e. 750/1000. So an “18-karat ring with 0.27 ct” tells you both at once.
Curiosities about the carat
Things you probably didn’t know
- The carob myth
It is often said that carob seeds are remarkably uniform in weight. A study in Biology Letters (Turnbull et al., 2006) put that to the test: their weight varies about as much as the seeds of other plants. The name stuck anyway.
- One carat for the whole world
The 200 mg metric carat was adopted unanimously in Paris in October 1907 at the fourth General Conference of the Metre Convention. The USA followed in 1913, the UK in 1914.
- Invented by a jeweller
The term “4Cs” was coined by Robert M. Shipley, who founded the Gemological Institute of America (GIA) in 1931. It appears in newspapers in the early 1940s. Before that, “carat” was the only term all traders used consistently.
- 3,106 carats by post
The largest rough diamond ever found, the Cullinan, was discovered in South Africa in 1905. While a decoy stone travelled under guard by ship, the real diamond was sent to London by ordinary registered post in a plain box.
- 530 carats in the crown jewels
Among the stones cut from the Cullinan by Asscher in Amsterdam is the Cullinan I, at around 530 ct. Today it sits in the Sovereign’s Sceptre of the British Crown Jewels.
According to Guinness World Records, the most expensive diamond ever sold at auction is the “CTF Pink Star”: 59.60 ct, internally flawless and pink, sold at Sotheby’s Hong Kong in April 2017 for US$71.2 million.
Real diamonds at 4D OUTFITTERS
Our fine gold jewellery features only real gold, natural mined diamonds and high-quality gemstones – from delicate rings and stud earrings to necklaces, bracelets and engagement rings. Pieces from our GIA Premium line come with GIA certificates for their diamonds.
The difference between 0.06 and 0.27 ct is best seen in person, with personal advice in our boutique in Bregenz. Online, shipping is free from €200, you have a 14-day right of withdrawal, and as a member of the 4D Insider Club you collect stars with every purchase. Questions? Write to us at service@4doutfitters.com.
More about diamonds: Diamonds as an investment: what you should know before buying and Natural and synthetic diamonds compared.
FAQ about carats
How much does a carat weigh?
One carat (ct) weighs exactly 200 milligrams, i.e. 0.2 grams. It is divided into 100 points of 2 mg each.
What does the ct figure mean on jewellery with several stones?
It usually refers to the total weight of all the diamonds. 26 brilliants with 0.27 ct weigh 0.27 ct together, not each.
Is carat for diamonds the same as karat for gold?
No. For diamonds, carat measures weight; for gold, karat measures purity. 18-karat gold means 750 parts pure gold out of 1000.
Is a heavier diamond always more valuable?
Not automatically. With the same colour, clarity and cut, the heavier stone is rarer and usually more expensive. But a large stone with a poor cut can be worth less than a smaller, perfectly cut one.
This article is based on an idea by jewelry.gio.
Your 4D OUTFITTERS team, Bregenz
Leave a comment
This site is protected by hCaptcha and the hCaptcha Privacy Policy and Terms of Service apply.