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Diamond Education

The 4Cs Of Diamonds

Searching for a sparkling diamond? Selecting a diamond starts by understanding the unique characteristics of each stone. Diamonds are graded based off the 4Cs - cut, color, clarity and carat weight. The 4Cs of diamonds impact the stone’s beauty and value. Learn more about each of the diamond 4Cs below. 

Diamond Cut


Cut measures how well-proportioned a diamond’s dimensions are including the balance and brilliance of its facets. 
Diamond cut is considered the most important of the four Cs.

Diamond Color


Diamond color refers to how colorless a diamond is. Color is the second most important of the 4Cs of diamonds. 
The less color, the higher the grade. 

Diamond Clarity


Clarity assesses small imperfections within a diamond. Inclusions can occur naturally during the diamond forming process. 
Clarity is used to quantify and specify any inclusions. 

Diamond Carat

Carat Weight

Carat measures a diamond’s weight. An objective measurement, carat weight is the most popular indicator for showing how large a diamond is. 

Diamond Shape


Though not one of the 4Cs, shape is still an important factor to consider when buying a diamond. Each shape has different attributes 
that can affect price and quality grades. 

Diamond Certification


Diamond reports and certifications can provide the full information on a diamond’s cut, color, clarity and carat weight. Unbiased diamond grading reports are offered with every Blue Nile diamond. 

Putting It All Together With Diamond Quality

As the largest online diamond retailer, we offer a vast collection of the world’s finest cut diamonds. Our diamonds are pre-selected for exceptional quality with well-graded elements of the 4Cs: cut, color, and clarity. 

Each of the individual 4Cs of diamonds may interact with one another to impact a stone’s overall appearance. For example, an ideal cut diamond may appear less brilliant if its color rating is L or M. A well-cut stone may appear larger than a diamond of the same carat weight thanks to increased light reflection. 

The 4Cs of our loose diamonds are evaluated based on a standardized grading scale. Each loose diamond is accompanied by a grading report from either GIA, AGSL or GemEx, independent diamond grading labs with stringent grading and certification guidelines to analyze diamond quality.

Chart displaying the Cut, Color, and Clarity grades carried by Blue Nile compared to low quality grades not carried by Blue Nile.

Fancy Shapes And The Four Cs Of Diamonds

While round brilliant is the most popular diamond shape, there are many other shapes available. We offer nine different fancy-shaped diamonds that bring a personality all their own. Also known as fancy-cut stones, these diamonds are still graded by their cut, color, clarity and carat weight. 

The 4Cs of diamonds can behave a little differently for fancy cuts. Cs such as clarity and carat can be more forgiving in fancy-shape diamonds. Larger tables can make these diamonds appear larger, maximizing a lower carat weight. Inclusions that are a consideration for round diamonds may be disguised or removed altogether in more specialized cuts. Fancy-shaped diamond 4Cs are also unique in terms of clarity, with different shaped stones adding their own faceting to the mix. 

Colorful Diamonds

While diamond color is one of the four Cs in respect to how colorless a stone is, there are some diamonds where colorful hues are intentional and even prized. Colored diamonds are available in hues of yellow, pink, green, blue and even brown. For fancy color diamonds, color isn't about how colorless the diamond is, instead it’s about the stone’s hue, intensity, overtones and saturation. When shopping for colored diamonds, the Cs of cut, clarity and carat weight are also still important. 

How To Buy A Diamond

With so many diamonds for sale, there are a lot of options to choose from. Buying a diamond doesn't have to feel like a guessing game. Learning a little about the 4Cs, diamond quality and how these influence diamond price can make the buying journey a simple one. Every purchase is unique, but there are some core steps for buying a diamond that you can expect to navigate as you find the perfect fit.

Diamond Buying Guide FAQs

What grade of diamond is best?

Our Astor diamonds represent the highest-graded stones available. These diamonds feature unparalleled brilliance.

Which of the 4Cs of diamonds is most important?

Cut is the most important characteristic of the 4Cs. Cut is responsible for the diamond’s brilliance. A symmetrical, proportionate diamond cut will bring the most sparkle.

Which of the diamond 4Cs is least important?

Clarity is believed to be the least important of the four Cs. This is because many imperfections are difficult to see with the naked eye.

How do the 4Cs impact a diamond’s price?

The higher quality a diamond is, the more expensive it will be. Each stone is unique and many less-than-perfect grades in some of the 4 Cs are difficult to see with the naked eye. For example, stones with a lower clarity score may still look eye-clean. Because of the uniqueness of diamonds, it’s possible to choose a stone with lower scoring elements of the 4Cs and still enjoy a breathtakingly beautiful diamond.