Diamond Buying Guide

A good understanding of diamonds is essential if you want to get the best quality and price.

gia certificate

GIA Certificate

To select the best diamond, you will need to start with the diamond’s certificate (also known as a grading report). The certificate will give you detailed information about the “4 C’s” that you’ll need in order to make the correct buying decision. All quality center diamonds will come with a certificate. The two most respected are GIA (Gemological Institute of America), and AGS (American Gemological Society). They both are well recognized for their accurate grading standards. At the high end, AGS is often preferred because of their more comprehensive cut and light performance specifications.

Where to Start When Buying Your Diamond

Choosing a diamond centers on selecting the shape, size, color, clarity, cut and quality. Let’s start with the shape…

Diamond Shape

Diamonds are offered in several different shapes. The three most popular shapes that we will cover in this guide, are the Round cut, Princess Cut and Cushion cut. Selecting the diamond’s shape is all about personal style and preference.

diamond shapes

There are those that say that “personality traits” may help predict which diamond shape your bride-to-be will prefer…

  • Round: traditional romantic
  • Princess: trendsetter and outgoing
  • Cushion: style and romance

The round is the most popular, followed by the Princess, with the cushion recently coming into fashion.

You can visit our Diamond Shape Guide and Does Your Diamond Reflect Your Personality pages for more ideas.

The Four C’s

Once you’ve chosen the shape of the diamond, it comes down to selecting the diamond’s size and quality, which brings us to the “Four C’s” – cut, color, clarity, and carat weight.


Everyone knows about carats. It’s how big the diamond is, and the bigger the better! However, technically speaking, a carat is a measurement of the diamond’s weight, not its size. (One carat is 200mg). Depending on how a diamond is cut, two diamonds of the same carat weight can appear visually slightly larger or smaller from one another. But in general, the more carats, the bigger the diamond appears.

Large diamonds are expensive. Due to the scarcity of larger diamonds, the price of a diamond grows exponentially as its size increases. According to a recent survey by The Knot, the average size of an engagement ring’s center diamond is 1.1 carats. What size you can afford will depend on your budget and the quality (cut, color, clarity) of the diamond…


Cut can be confusing, because the diamond industry uses it in two different ways. One, is in describing the diamond’s shape, such as Round cut, Princess cut, etc.

diamond cut

The other use, which is the one listed in a GIA or AGS grading report, is in describing how well proportioned the diamond is. The better a diamond is proportioned, the better its light performance: sparkle, brilliance, scintillation and fire.

In general, try to stick to diamonds graded Excellent or at least Very Good. At the high end are diamonds considered “Super Ideal” or “Hearts and Arrows” quality.

Like carats, the better a diamond is proportioned, the more expensive it will be. But unlike carats, the price doesn’t grow exponentially. An Excellent cut diamond is only about 15% more expensive than a Very Good cut. So unless you’re on a tight budget, select an excellent cut; you’ll get a bit more added sparkle if you do.


The term color is a measurement of the degree of yellowish tint that is visible in a “white” diamond. Graded on an industry-standard scale from D (colorless) to Z (light yellow), the less yellowish tint visible in the diamond the more expensive it will be.

diamond color

Most people find the best value in the G,H,I and maybe J (near colorless) range. These diamonds can be thousands of dollars less expensive than the D,E,F (colorless) diamonds, yet color-wise, almost indistinguishable from their more expensive counterparts.


A diamond’s clarity is a measurement of how many imperfections it has. Diamonds are graded on a scale from F (flawless), IF (internally flawless), VVS1-VVS2 (very very slightly included), VS1-VS2 (very slightly included), SI1-SI2 (slightly included) through I1-I2-I3 (included).

diamond clarity

In general, imperfections in diamonds rated F/IF through VS1-VS2 will not be visible to the unaided eye.

The best value will be in diamonds rated VS1 or VS2.

You can find great value in SI1/SI2 diamonds, but you need to examine them visually to make sure they are “eye clean”. For example, James Allen’s “360° Diamond Display Technology” lets you view a magnified video of each diamond in their inventory. So with a little extra work, you can save yourself quite a bit of money.

For more information on the Four C’s, take a look at our Diamond Pricing and the Four C’s guide.

In addition to the 4 C’s, there are a few other factors to consider when selecting your diamond, specifically: Polish, Symmetry and Fluorescence. Visit our Diamond Anatomy and Pricing page for more details.

…Continued in Part Two of our Diamond Buying Guide.