Diamond Carat with Loupe and Gia Certificate | Lisa Robin

Diamond Guides

Diamond Carat

When purchasing diamonds, the carat weight is a crucial factor to consider. Although it may appear to be a straightforward measurement, there is more to it than meets the eye. Here is what you should be aware of.

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What is Diamond Carat?

Diamonds are sold by weight using a measure of metric units known as carats. It is common for carat to be used as a reference to the size of a diamond. The size of a diamond is measured in millimeters.

To better understand, one carat equals 200 milligrams, 0.20 grams, or 1/5 of a gram. To give you a reference, 142 carats are equivalent to one ounce. Carat is the standard unit of weight for diamonds and most other gemstones. Carat is abbreviated "ct," or "ctw" or “twc” for total carat weight when referring to the carat weight of multiple diamonds. Generally, weights are expressed with two decimal points, such as 1.00 ct, 0.76 ct, or 1.57 ct. A carat comprises 100 points, abbreviated as "pt." Thus, 1.34 ct represents one carat and 34 points.

how does diamond shape affect the appearance of size?

Not all equally-weighted diamonds will look the same. Diamond shape is a factor in how big a diamond appears, as well as diamond cut.

Diamond Size vs Carat Weight | Lisa Robin

DIAMOND shape and appearance of size

Large diamonds are rarer than smaller ones, and as the carat weight increases, the value of the diamond increases as well. However, the increase in value is not proportionate to the size increase. In other words, a diamond that is double the size of another will likely be more than two times the cost.

During the certification process, in addition to weight, the dimensions of a diamond are also assessed. An optical measuring tool measures the diamond's length and width in millimeters, as well as its proportions and facet angles. These measurements assist in determining its cut grade.


Often the first criteria discussed when selecting a diamond is carat weight you would like to buy and in that context is referring to a relative size. It is helpful to consider cut and color which have the most visual impact, followed by clarity. You may find compromising slightly on carat weight within the cut and color range you prefer will adjust purchase price.

However, it is essential to note that diamonds of the same weight may not appear to be the same size. Poorly cut diamonds may seem smaller than their weight or lack brightness. All other things being equal, a diamond's price rises as its carat weight increases. Carat weight also allows you to compare prices between diamonds with varying weights but similar color, clarity, and cut grades, enabling you to compare the per-carat cost of each stone to find the most excellent value.

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That’s why we are here to guide you through every step - from understanding what carat, color, cut and clarity mean, to designing the perfect ring.

About Diamond Cost

Remember that a gemstone's carat weight varies from its physical dimensions when shopping. While a larger stone will weigh more, it is not always true that it will appear larger or offer better value. For example, diamond cut with more depth may have weight hidden below the girdle, making them heavier without increasing attractiveness.


The only diamond shape to receive a ‘cut grade’ are round brilliant cut diamonds. However, you should ensure any other diamond shape has Excellent symmetry and polish grade, or at least Very Good. ‘Brilliant cut’ diamonds are designed to exude the most sparkle. Step cuts feature larger, parallel facets that celebrate the clarity of the stone with more subtle flashes of light

Brilliant Cut Diamonds

By far the most popular diamond shape, round diamonds are more than 50 percent of all diamonds sold. The reason for their popularity is due to their brilliantcut.

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Step Cut Diamonds

Step cuts have a distinct geometric appearance. They are different from other diamond cuts in that their facets are arranged in a series of steps

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Diamond Guides
What Is Diamond Cut