GIA vs. AGS Diamond Certification and Cut Grades


GIA is one of the best diamond grading laboratories in the world due to their reliable and stringent grading standards. Founded in 1931, GIA maintains its non-profit roots and continues to grow in technological innovation to maintain the highest standards in education, research, lab services, and instrument development. Some of their most notable achievements have been found in the development of the now industry standard D-Z color scale and Flawless-I3 clarity scale, detecting fracture filled diamonds, and identifying the affect of fluorescence on a diamond’s appearance.



In 2006, GIA issued a 5-grade, proportion-based quality system for round brilliant colorless diamonds for the first time. This new scheme relies upon a 2-dimensional system to determine a diamond’s cut grade. As a result, GIA certs not only include the usual crown and pavilion angles but also lower girdle and star facet information.

However, this new addition to GIA’s grading certification has also become an industry wide downfall. Many have criticised GIA for being too lenient on deeper and steeper cut stones which can be a direct disadvantage to many retailers and consumer’s relying upon GIA’s “Excellent” cut specifications. In other words, GIA’s “excellent” cut grade includes a very wide range of cut parameters with around 50% of the diamonds submitted to the lab getting this cut grade.


example of a GIA grading report

example of a GIA grading report


Since GIA has come out with their new cut grade parameters (in 2006), many diamond cutters are using this to their advantage. For example, diamond cutters are knowingly cutting stones to the maximum possible weight that is acceptable within the “excellent” weight grade while still maintaining the price premium for an excellent graded stone. And remember, a GIA excellent cut stone has nothing to do with hearts and arrows symmetry; which is an entirely different subject pertaining to specific cut and facet proportions.



Although GIA “Excellent” cut grade is still considered an elite grading, it is important to know that the American Gem Society (AGS) cut grading system uses a more advanced 3-dimensional system to determine a diamond’s cut. Additionally, AGS utilizes human analysis, an angular spectrum evaluation tool  (ASET),  and optical physics ray-tracing software to determine the quantity and quality of light that is returned to the observer (in motion as well as in a face-up static position).



All of these tools help to give AGS an overall summary of the interaction of light within any given diamond and therefore is used to determine if a diamond’s cut is AGS “Ideal Light Performance” grade. Because the AGS cut evaluation process is very stringent and exact, (given to less than 1% of all diamonds in shapes where cut is graded), the AGS 0 ‘Ideal’ grade is the world’s strictest laboratory standard for cut.


example of an AGS diamond grading report

This is an example of an AGS diamond grading report. Note the red ASET (Angular Spectrum Evaluation Tool) image. This vital piece of information shows the expected “light performance” on a given stone. Red is the most desirable color in any ASET image as it indicates high light reflection. Blue represents contrast and Green is lower intensity light reflection. This particular diamond is a “Super-Ideal” Hearts and Arrows diamond cut by Brian Gavin.



What Does All This Mean To The Diamond Consumer?



– GIA’s cut grade system is based on proportions and is not advanced enough to assess individual diamonds on an individual basis (like AGS does).



– GIA also issues deductions for finish factors of polish and symmetry that has resulted in the penalization of some super-ideal diamonds that have no known performance issues.



– The top GIA cut grade, “Excellent,” overlaps several AGS cut grades.



– GIA allows for the cut grade to range too wide allowing for diamonds with proportions that are farther away from Tolkowsky’s Ideal cut. This includes a number of steep/deep diamond combinations that can make a diamond look smaller than its carat weight implies. This can also result in significant light leakage.


So Which Lab Is Better?



Undeniably GIA has the largest global reputation for consistent high quality reports, and is known for their strictness in color, clarity and finish grading (while allowing more freedom in their cut grades). Since GIA caters to a more global taste in certified diamonds, it makes sense that their wide cut grade is appealing and available for different markets.


AGS on the other hand provides a service to consumers that is more boutique with a more narrow margin in cut grade parameters. Diamonds that receive the AGS ideal grade were more likely sent there because the manufacturer was confident enough to know it would receive this high pedigree. More than 97% of all diamonds fail to meet AGS 0 “Ideal” cut requirements and that is perhaps why many commercial diamonds are sent to labs with more lenient cut grading or perhaps no cut grade at all. If you are buying a diamond online then AGS is preferred as it is the world’s strictest laboratory standard for cut.

Online Diamond Buying Advice Recommends!


Whiteflash- “Most visually balanced diamonds in the world.” Whiteflash has the largest inventory of super-ideal hearts and arrows round and princess cut AGSL diamonds in the world and offers some of the top leading luxury bridal and jewelry designs by: Veraggio, Ritani, Vatche, Leon Mege and Benchmark. Be sure to check out our Whiteflash review and read recent diamond Q&A for tips how how to buy your perfect diamond!


Brian Gavin Diamonds- Brian “The Cutter” is a 5th generation diamond cutter originally from South Africa. Brian offers super-ideal round brilliant, princess and cushion cut diamonds; all cut to his meticulous high cutting standards. Brian Gavin is the only retailer that specializes in super-ideal blue fluorescent diamonds, an industry specialty that offers the same hearts and arrows perfection at a fraction of the price. Read our Brian Gavin review for a our actual diamond buying experience with them and learn more about how to buy a diamond with our recent diamond Q&A from our readers!


Zoara- Specializes in certified GIA and AGS loose diamonds sold at the ultimate lowest prices on the internet. All diamond color, clarity, carat weight and cut parameters are available to suit any customers taste and budget. Zoara has actual REAL diamond pictures available for many of their diamonds which helps with clarity assessment. Be sure to read our Zoara review for our diamond buying experience and read up on our recent ODBA readers diamond Q&A for diamond buying tips and advice.


Ritani- High-end Jewelry brand specializing in micro-pave engagement rings that are all handcrafted in New York. All GIA and AGS graded diamonds are owned by Ritani allowing for FREE In-Store preview of a customer’s made-to-order engagement ring. No other online or retail store does this!


Blue Nile- “Forbes Favorite” online jeweler and still the favorite of many online shoppers. Read our very popular Blue Nile Review on how to buy a round brilliant diamond ‘step-by-step’. Readers ask questions all the time about buying from Blue Nile, so be sure to check out our recent diamond Q&A!

Don’t be shy! Please feel free to CONTACT ME with any of your diamond questions! Check out what others had to say about ODBA at

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