Demystifying Diamonds One Carat At A Time: Part 1

January 18th, 2017 | Stephanie Dore


There is so much information (and a lot of misinformation) around buying a diamond that it can be hard to know what’s true. We’re here to demystify some of the most commonly asked questions, with advice straight from our experts.


How big is a carat?

One of the most common diamond buying myths is that “carat” refers to a diamond’s size. In fact, “carat” is a measure of weight—like an ounce or pound—equal to 0.2 grams. A diamond’s visual size is determined more by its cut and proportions than by its weight.

There are several aspects to consider when determining how large a diamond will appear. The first is shape. We carry 10 of them: round, princess, oval, emerald, Asscher, marquise, pear, radiant, cushion, and heart. These shapes can vary greatly in how their weight is distributed.

Second, consider a diamond’s physical measurements—the diameter, or distance across the top—listed in millimeters. This is how the stone will be viewed when set face up into a ring.

Lastly, consider a diamond’s cut grade, which takes into account the proportions and weight distribution of the diamond. Two diamonds of the same carat weight can appear quite different in size based on how well they’re cut. A higher cut grade means optimal light performance, which can actually make a diamond appear larger.

Is a 1-carat diamond double the size of a 1/2-carat diamond?

While generally the size of a diamond is proportional to its carat weight, just because a diamond is twice as heavy doesn’t mean it is twice as large. The average 1/2-carat round diamond is approximately 5.1mm in diameter, while the average 1-carat is 6.4mm. Carat weight will give you a general idea of diamond’s size, however physical measurements and cut grade should also be taken into consideration.

A good thing to note is that diamond prices throughout the industry jump significantly at the half-carat and full-carat marks. To get the best value, look at diamonds just below these sizes. For example, a 0.90-carat diamond instead of a one-carat. You’ll see a big difference in value, but you’ll never notice the difference in size.

Do I need to buy a D color?

Buying a diamond is all about deciding what is most important to you. For purists, that might mean an absolutely colorless (D grade) diamond, but the best values can be found in Near-Colorless grades from G to J.

Of the 4Cs, (cut, color, clarity, and carat weight) color is the second most important (next to cut, which determines brilliance) because it is the second most detectable quality to the naked eye. Color often shows up as pale yellow or warm tones and is typically undetectable in Colorless (grades D-F) and Near-Colorless (grades G-H) diamonds. If color is a characteristic that matters to you, you have leeway between the extremely rare (and higher priced) D-graded diamonds to the more common, (and budget friendly) H-graded diamonds to find the right stone for you.

Another thing to keep in mind is that the metal color of the setting you chose can balance out the color inherent in a diamond with a lower color grade. For example, a white metal, such as platinum or white gold can offset any yellow tones. A Blue Nile Diamond and Jewelry Consultant can help you make that choice.

Will I see color in an I- or J-graded diamond?

While Near-Colorless, I- or J-graded diamonds might have a detectable warmth or slight yellow tone to them, it is difficult to see unless compared side-by-side against diamonds of higher grades. Keep in mind that as diamond size increases, color may become more noticeable, and the brilliance of a well-cut diamond will also mask some color.

Can I find an eye-clean SI1 or SI2?

While most diamond inclusions are so small they cannot be seen by the unaided eye, in SI1 and SI2 diamonds, it is more likely that those inclusions will be visible. As diamond size increases, so does the ability to see those inclusions. Inclusions are also more visible in Asscher and emerald-cut diamond, as they are designed with longer, clearer facets that emphasize their transparency. For these shapes, it is best to stick to VS1 or higher clarity grade to ensure inclusions will not be visible.

With our industry leading 360° diamond view technology, you can now get a magnified view of your diamond before you buy. Used in conjunction with the GIA Diamond Grading Certificate included with every diamond we sell, you’ll have all the details you need to make an informed purchase.


Read Part 2 for answers to more commonly asked questions.

January 18th, 2017
Stephanie Dore
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