Diamond carat (ct)

One of the key characteristics that determines a diamond’s value is its weight – the diamond carat. And in general, the larger the diamond, the more valuable it is.

Karat vs. diamond carat

The weight of a diamond is measured in carats, and should not be confused with karat, which is used to describe the purity of gold.

Learn more about diamonds

1 diamond carat = 0.20 grams

1.00 carat is the same as 0.20 grams, so a diamond of 5.00 carats weighs exactly 1 gram.

A diamond carat is an ancient unit of weight that has been used by diamond dealers for many thousands of years. The unit originates from India, where some of the first diamonds were excavated and treated. To weigh the diamonds, they used seeds from the carob tree as weights, with a dried seed weighing about 1.00 carat.

A diamond’s carat can be calculated using a formula

A diamond’s dimensions determine its weight. The carat weight of a well-proportioned round brilliant cut diamond can be calculated using a special formula, which is precise for exactly 95% of round brilliant cut diamonds.

In general, however, the carat is measured with specialised tools to ensure precise, accurate measurements. Diamond carat weight is always expressed to two decimal places.

The value of the diamond’s carat increases exponentially

The larger the diamond, the rarer and more valuable it is. But a diamond of 1.00ct is not just twice as valuable as a stone of 0.50ct with the same characteristics – it is actually significantly more valuable as the price rises exponentially.

This means, for example, that the size difference between a 1.00 carat diamond and a 0.99 carat diamond is not visible to the naked eye, but the difference in price can easily amount to more than several thousand Danish kroner.

The Big Hole

In 1871, a gigantic diamond of 83.5 carats was discovered in South Africa at DeBeer’s farm. This was the start of the world's first ‘diamond fever’ and the beginning of the Kimberley mine.

content-image The Big Hole in South Africa

During the first 40 years of the Kimberley mine, 50,000 miners worked with picks and shovels to penetrate deep into the earth’s interior, creating what has since been known as ‘The Big Hole’ – an excavation measuring 240 metres deep and 463 metres wide. The excavation continued to a depth of 1,097 metres. Fortunately, the work bore fruit. In the period from 1871 to 1914, 2,772 kg of diamonds were excavated, equivalent to 14 million carats.

The Cullinan Diamond becomes the Star of Africa

In 1905, a miner found a 3,106.75 ct diamond. It was named after the mine’s director, Sir Thomas Cullinan, and is the largest rough diamond that has ever been found.

Legend has it that Cullinan had a copy of the diamond made in glass and sent it by ship to London as a diversion. The real diamond was sent by post!

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The nine largest diamonds found in the Cullinan mine

The Cullinan Diamond was later taken to Amsterdam, where diamond cutters the Asscher brothers spent 6 months analysing it in terms of how best to cut it.

The Cullinan Diamond was then cut into ‘smaller’ parts. The biggest part became the Star of Africa, and with its 530.20 carats, it is the world’s largest cut diamond. The diamond is a pear-shaped gem that is set in the Sovereign’s Sceptre, part of the Crown Jewels of the United Kingdom. A further eight large diamonds, which are now also part of the Crown Jewels of the United Kingdom, as well as 96 smaller brilliant cut diamonds were cut from the Cullinan Diamond.

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