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Diamond Carat Explained

When buying a diamond or gemstone, one of the most important factors to consider is the carat weight. The carat is a unit of weight used to measure diamonds and other gemstones. One carat is equal to 200 milligrams, 5 carats equals 1 gram.


The carat weight of a diamond is important because it is directly related to its price. In general, diamonds and gemstones with a higher carat weight are more expensive than diamonds and gemstones with a lower carat weight. This is because larger diamonds and gems are rarer and more difficult to find.




Diamond Carat Sizes
Diamond Carat Compared

Diamond carats and cost

The price of a diamond or gemstone does not increase in a linear way when the carat weight increases. Instead, the price increases exponentially. You might expect a 2 ct diamond to be twice as much as a 1ct of same qualities, however this is far from the case. For example a 1ct E VS1 round diamond might be $10 000.00 , yet a 3ct E VS1 is $109 500.00 total. Which is 10 x the price, not 3 x the price which is a common misconception.





Diamond carat weight to price graph
Exponential increase in Price per Carat as Diamond Carat Weight Increases

There are a few reasons why the price of a diamond or gemstone increases exponentially with carat weight.


First, larger gemstones and diamonds are much rarer than smaller stones. This is because the chances of finding a large diamond or gemstone are much lower than the chances of finding a small diamond or gemstone.


Second, larger diamonds and gems are more difficult to cut and polish. This is because they are more fragile and can easily be damaged during the cutting process. It is far more risky and losses are more frequent.


Third, larger diamonds and gemstones are more visually appealing than smaller ones. This is because they have a larger surface area and reflect more light. When it comes to coloured gemstones, larger carat weight and size usually hold more intense colour.


Not all "carats" are the same

Specific gravity is the ratio of the density of a gemstone to the density of water. It is a measure of how heavy a gemstone is compared to water. Gemstones with a higher specific gravity are denser and will weigh more than gemstones with a lower specific gravity.

Diamonds have a specific gravity of 3.52, which is one of the highest of all gemstones. This means that a 1 carat diamond will be smaller in size/dimension than a 1 carat gemstone with a lower specific gravity. For example, an emerald has a specific gravity of 2.67, so a 1 carat emerald will be larger in size/dimension than a 1 carat diamond.


In addition to specific gravity, there are other factors that can affect the visual size of a gemstone. These factors include the cut, clarity, and color of the gemstone. A well-cut gemstone will appear larger than a poorly cut gemstone of the same carat weight. A gemstone with few inclusions will also appear larger than a gemstone with many inclusions. And a gemstone with a vibrant color will appear larger than a gemstone with a dull color.





How is diamond carat weight decided

Carat Scale
Diamonds and Gemstones are weighed using precision carat scales.

Diamond and gem cutters are experts in maximizing the value of gemstones. They know that the carat weight is one of the most important factors that affects the price of a gemstone. Therefore, they will often cut a gemstone to be as close to the upside of 1 carat as possible, even if it means sacrificing some clarity or color.


For example, a cutter might have a rough diamond that weighs 3.00 carats. After careful consideration of shape and clarity they decide to cut it into two stones to get maximum value. One that is 0.97 carats and one that is 1.01 carats. However, the 0.97 carat stone will be worth much less than the 1.01 carat stone, even though the difference in weight is only 0.04 carats. They may decide to take less weight off of the 0.97 ct stone to keep it over a carat but it would mean that the stone would not be as clean ( clarity) and therefore less value per carat. Gemstone and diamond cutting is a constant balancing act between size, clarity, colour and carat weight.


The reason for this is that there is much more demand for 1 carat stones than for stones that are just under 1 carat. This is because 1 carat stones are the most popular size for engagement rings and jewellery. As a result, there are far fewer 0.90+ carat stones than 1 carat stones, however this doesn't always mean a bargain as they are harder to find.


If you want to know more about gemstone and diamonds, I'm happy to help you. Just contact me or book an appointment in Harrogate or London and I can answer any questions you have and help you find the perfect gemstone or diamond for your needs.


For all your fine gemstone and diamond needs in Harrogate, the UK or worldwide.


Clayton Delville

Clayton Delville Hood

Clayton is a GIA graduate gemologist, Diamond and Coloured stone grader and dealer with over 20 years experience in the Diamond, Gemstone and Jewellery business. More...

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