What Is the SI Diamond Rating?

Choosing a perfect diamond may be impossible and costly, but choosing the perfect diamond for you is made possible by understanding the characteristics that make up a diamond. When selecting a diamond one of the key elements to look for is clarity.


Clarity refers to how visible the appearance of any feathers, clouds or tiny crystals, all referred to as inclusions, are to the naked eye or under a 10x magnification. Clarity is broken up into six categories. The clarity of your diamond could fall under any of the six classifications: flawless (F), which has no inclusions; internally flawless (IF), which has no internal inclusions, but some external inclusions; very very slightly included (VVS1 & VVS2), which has minute inclusions that are very difficult to detect even under 10x magnification; very slightly included (VS1 & VS2), which has minute inclusions that are seen with some difficulty under 10x magnification; slightly included (SI1 & SI2), which has minute inclusions that are easily seen under 10x magnification, but not the naked eye; and included (I1, I2 & I3), which has inclusions visible both to the naked eye and easily under 10x magnification.

SI Diamond Rating

A diamond falling under an SI (slightly included) clarity rating means it has inclusions that are visible under 10x magnification and unlikely to be visible to the naked eye.

SI Scale

The SI ratings range from SI1 to SI2, and sometimes SI3 in an ascending scale of inclusions, thus SI1 contains the least inclusions among the SI class.

Clarity and Cost

Clarity affects the cost of your diamond. For example, if you have a 1.00 carat diamond with a G color and SI1 clarity, to move from SI1 to a VS1, you will pay approximately an additional $1,000 per carat. VS1 clarity has minute inclusions seen with difficulty under 10x magnification and so is one class up from an SI rating. SI rated diamonds are good for those with a budget but still want a diamond that is clear to the naked eye.

SI Diamond Rating Value

A diamond's clarity affects the value, not the unmagnified appearance.