1.) Carat Weight

"Carat Weight" is simply the weight of the diamond (Size).

By definition, 1 carat is exactly 200 milligram. Since most diamonds sold in the jewelry industry weigh less than 1 carat, the carat is usually subdivided into "points." There are 100 points in 1 carat, so that a diamond weighing 3/4 carat would be a "75 point diamond." In summary:

1 carat= 200milligram= 100 points

diamond sizes

2.) Clarity

FL: Completely flawless (No internal or external characteristics)

IF: Internally flawless; only external characteristics are present, which can be removed by further polishing the stone

VVS1 - VVS2: Only an expert can detect the internal characteristics with a 10X microscope. By definition, if an expert can see internal characteristics from the top of the diamond, it is a VVS2. Otherwise, if an expert can only detect flaws when viewing the bottom of the stone, then it is a VVS1

VS1 - VS2: You can see the internal characteristics with a 10X microscope, but it takes a long time (more than about 10 seconds)

SI1 - SI2: You can see the internal characteristics with a 10X microscope

I1 - I3: You can see the internal characteristics with the naked eye. Consider avoiding I2-I3 diamonds.

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vvs-diamonds si-diamonds

3.) Color

The "color" of a diamond refers to its degree of "yellowness." The ideal diamond is completely colorless, and therefore it will be the most expensive. The Gemological Institute of America (G.I.A.) grades color alphabetically from D (totally colorless) to Z (yellow)

diamond color chart

diamond colors

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4.) Cut

Proportions

In an ideally-proportioned diamond, all of the light entering the diamond from the top will bounce within the diamond and be reflected back through the top, giving the stone maximum brilliance and fire. If the stone is too shallow or too deep, some light will escape through the bottom part of the diamond, giving the appearance of shadows when viewed from the opposite side.

diamond cut chart

It's easy to see that the deep-cut diamond shown above will have a higher carat weight, but is clearly the less desirable stone! Many jewelers will not discuss cut proportions unless the customer specifically asks; a stone rich in carat weight but poorly proportioned can be deeply "discounted," giving the buyer a false impression of a great deal.

ideal cut diamond light refection

Common Proportion Metrics
In order to assess how well a given diamond is cut to ideal proportions, you will have to measure the diamond. If the stone has a G.I.A. certificate, the measurements will be on the certificate. Otherwise, ask the jeweler to perform the measurements in front of you.

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Don't be a perfectionist. It is acceptable to purchase a diamond that rates "good" or even "fair/poor" on any category, as long as you are AWARE of what you're purchasing and understand the cost and quality tradeoffs.

diamond cut expl