Round Brilliant Diamond Ideal Proportions

By Thomas J Stevens GIA DG CSG - Last modified December 27, 2019
Reading time: 10 minutes

Holding hands. Woman wears a diamond ring.

Why Diamond Certificates

Getting What You Paid For

If someone wants to sell you a tiny sparkly stone and tells you it is a 1.00ct D color, VS2 diamond, how do you know he got that description right? That little stone may or may not be what he says. He may or may not be trying to mislead you. But what if the diamond is actually a lab grown 0.98ct F SI2 diamond? It would probably be worth a lot less than his asking price. Let’s give him the benefit of the doubt. What if he is not deliberately trying to mislead you but is simply mistaken? You’d likely still be paying him more than you would elsewhere. Well, all this kind of confusion and uncertainty is easily solved with a paper issued by a gemological laboratory. This paper is called a diamond grading report. This report gives you the down low on the diamond. Grading reports are often referred to as Certs or Certificates, though labs don’t usually label them as such. They are grading reports. See the list of various names for grading reports below. Once provided with a grading report you don’t need to rely on the dealer’s memory nor merely on his word. If you want to know that you are getting what you have been promised always, always buy a diamond that has been issued a grading report. Now, just be aware that there are a number of different labs, so make sure the grading report was issued by a reputable lab. GIA, AGS, HRD and IGI, and EGL are the most well known labs. Other labs do exist but can sometimes lack the standards shared by the big five. I recommend GIA, AGS, IGI grading reports. HRD is more widely used in Europe. EGL-USA is also a good lab, though a few years ago there was a bit of a scandal involving some EGL labs overgrading diamonds and it’s taken some time to recover their reputation.

Certificates Are Very Useful

Occasionally someone gets tempted to buy an uncertified diamond. But this invariably ends badly. You absolutely must insist on a diamond grading report to accompany your diamond purchase.. And make sure it is from one of the reputable grading labs.

The number one reason a certificate is necessary:
If a diamond is “uncertified” you can bet your bottom dollar it is overgraded by a grade or two. The same is the case for color grades, as incredible as this sounds. Since in the US the FTC actually allows for some error when selling ungraded diamonds it stands to reason that this will be taken advantage of. An in-house or in-store graded diamond is rarely the grade it is purported to be.

Simply insist on getting a diamond with a grading report issued by either GIA, AGS, IGI or EGL-USA. The grading must be performed by a party that has no financial interest in your diamond. There are way too many diamonds quoted as, say a H color / VS-1 clarity that simply aren’t. Were they to be graded by a lab they would be downgraded.

If you stick to buying only diamonds that have a diamond grading report issued by a trustworthy lab you will never have that uneasy feeling that maybe your diamond is not worth what you thought it was.

It’s just too tempting for stores to have their stones overgraded by their buddies at the local lab or in some cases the tech may have a financial interest in the diamond jewelry concern. These are some of the reasons we end up with people overgrading stones. Another reason stones get overgraded is that the grading standards used at a small lab are often not consistent with the standards used by the major labs. The GIA Gem Trade Laboratory where the diamonds are graded as well as AGS labs both have the same definition when it comes to color and clarity. Of course carat is something that you would think is globally agreed upon. But there is a proper way to round off numbers used in the gem trade which is in the consumer’s favor. A certificate from one of these labs is the best way to get the diamond you want and avoid paying an E color price for a diamond which is in fact a G color.

A common fear that people experience when getting jewelry serviced or cleaned is whether a jewelry store will switch their diamond for an inferior one. If you are wondering how you be sure you will get the same diamond back when it gets cleaned or the ring repaired at a jewelry store then you will be happy to know that the grading report is what will be your security. Also I should clarify that is is highly unlikely that any jeweler would switch stones intentionally, accidents do happen, and it’s possible this could occur in a busy store. Having a certificate shows your diamond’s unique inclusions. These are like a fingerprint. It’s something you can check when picking up your jewelry. Laser inscription is also commonly done these days. This is usually the certificate number (on the girdle of the stone), and maybe a logo or diamond brand. Laser inscriptions can be seed with a jewelers’ loupe. Better safe than sorry. Just take a second to examine the diamond against your grading certificate and you are on your way.

Just as it’s the only way to prove the 4C’s of a diamond when buying a diamond, a grading report will be the only way to prove the same if ever the diamond needs to be sold. If you don’t have a grading report you may find it near impossible to move and you will end up having to fork out extra cash to have the stone graded just to be able to list it for sale.

A grading report can have important information which can help you assess whether you want the diamond or not. Some shapes such as round brilliant and Princess cut diamonds usually receive a cut grade. This saves you a lot of time as the cut grade includes important factors like whether the diamond’s girdle is an acceptable size, whether the diamond’s depth is a good ratio that does not make the stone too flat or too tall. The cut grade also gives you an indication as to whether the diamond returns light efficiently or not. It takes time to learn enough to properly assess all the factors relating to diamond quality and pricing. Most people are not going to take a six month course on gemology just to buy a diamond. A detailed certificate saves you time and energy. It is an expert evaluation that helps you understand the diamond better.

Only some diamonds qualify as investment diamonds, like the very rare colors and sizes. Investments are no good if they can’t eventually be sold. A certificate makes it so much easier to sell a diamond when the time comes to either trade up or sell it. Without a grading report you can’t get far in the sales process. You will find that there is no way around it. You will have to send your diamond to a reputable lab and get it graded if you want to sell it.

    • Overstated Grades
    • An Indication of Quality You Can Trust
    • Grading Must be Unbiased
    • Repairs: When You Definitely Need A Cert
    • Better Retention and Appreciation in Value
    • Valuable Information
    • Added Value for Investment Diamonds

Diamond Grading Reports

Here are the links to the diamond grading reports issued by

Gemological Institute of America Gem Trade Laboratory:

  • GIA Diamond Grading Report

    The GIA Diamond Grading Report is the staple of the diamond industry. It includes an assessment of the 4Cs – Color, Clarity, Cut, and Carat Weight – along with a plotted diagram of its clarity characteristics. It has a graphic representation of the diamond’s proportions. It includes a cut grade for standard round brilliant cut diamonds.

  • GIA Diamond Dossier

The GIA Diamond Dossier® is used for diamonds under 2ct but no smaller than 0.15ct. It includes an assessment of the 4Cs – Color, Clarity, Cut, and Carat Weight. The service includes inscribing the diamond with a microscopic laser inscription of the GIA report number. This makes it simple to match up a diamond to its dossier.

  • GIA Diamond Origin Report

    The GIA Diamond Origin Report also includes a complete assessment of the 4Cs: Color, Clarity, Cut, and Carat Weight. It also includes a plotted diagram of the diamond’s clarity characteristics, a confirmation of geographic origin, and laser inscription of GIA report number. This service is only for eligible earth made diamonds, weighing no less than 0.15ct, that have gone through rough analysis with GIA before polishing.

  • GIA Diamond Report Check

GIA’s online Report Check is available for all GIA reports, providing you with an additional level of assurance. With Report Check, it’s very easy to confirm that the information on your report matches the GIA database.

For reports dated on or after:

January 1, 2000

July 1, 2010

January 1, 2014

February 1, 2015

Report data





PDF (facsimile) of report





Image of item, plotted diagram, and/or
proportion diagram (where applicable)





Treatment Description Tab (where applicable)






American Gemological Society Laboratories has a number of different types of grading diamonds.

  • AGS Platinum Grading Report

    AGS Laboratories uses a scientifically vetted cut-grading system based on optical physics. The diamond’s performance is determined with proprietary ray-tracing software. This three-dimensional analysis is seen as the ultimate test for evaluating the performance of light in a diamond. This is the cornerstone of the Diamond Quality® Document (DQD) and the Platinum Diamond Quality® Document. See my article on How To Read an ASET Diamond Image for more information on the system employed for gauging the quality and light performance of a diamond.The performance-based cut grade is used by AGS for the most commonly found diamond cuts: Round Brilliant, Princess, Oval, Emerald and Cushion-shaped diamonds. All the detail of the Diamond Quality® Document as well as the patented computer-generated Light Performance map unique to each diamond are included in the Platinum Diamond Quality® Document. It’s really the ultimate grading report and one of the best ways for you to quickly assess the quality of a diamond. If a diamond jeweler doesn’t want to. When you are shopping, you appreciate the value of brands you know and trust. This concept is embraced by the diamond industry as well, from the retailer to the designers who create the jewelry. For diamond companies who have developed unique and patented cut designs, the AGS Laboratories offers the opportunity to provide a specialized proprietary version of the Platinum Diamond Quality® Document. This features the company's logo directly on the document. Brian Gavin Diamonds, for example has AGSL’s Platinum Diamond Quality® Document issued for their signature cuts.

  • AGS Diamond Quality Document

The AGS Diamond Quality® Document (DQD) provides clients and consumers with what could be considered the most detailed information available on a diamond. The Diamond Quality® Document is one of the most popular grading reports offered, showing cut (if available), color, clarity and carat weight, as well as a diamond profile showing measurements, a custom plot with the actual facet arrangement, and inscription details. To say that it is a completely comprehensive diamond grading report would be an understatement! The Diamond Quality® Document is the industry’s only grading report that offers a three-dimensional performance-based cut grade for the Round Brilliant, Square Princess, Emerald, Oval and Cushion-shaped diamonds. The Diamond Quality® Document is also offered in a “Platinum” option which is the partnered version as mentioned above. The AGS Diamond Quality® Document is the perfect way to assess Ideal Cut diamonds.

The Diamond Quality® Certificate is a super-powered grading report prepared by the AGS Laboratories exclusively for American Gem Society retail jewelers. It is a Diamond Quality® Document and a guaranty (guarantee) from the participating American Gem Society member store.
This report was created on the understanding that a diamond grading report is an opinion of the laboratory issuing the report. So while a diamond grading report is an expert opinion it is not a guaranty from a legal perspective. The Diamond Quality® Certificate changes that. It is a legal statement from the issuing AGS retailer, guaranteeing authenticity and quality, as well as certifying the diamond cut grade, color grade, clarity grade, and carat weight of the diamond. The Diamond Quality® Certificate is authenticated and validated by an American Gem Society diamond professional — either a Registered Jeweler, Certified Gemologist, or Certified Gemologist Appraiser.

The AGS Diamond Quality® Report gives you a complete grading analysis of a diamond. This included the diamond’s profile and its measurements on a custom plot. The Diamond Quality® Report is used for diamonds that not Ideal cut diamonds. So the cut, polish or symmetry, will show a maximum grade of AGS 1 (Excellent). Though the AGS Performance-based Cut Grade covers a variety of shapes, the Diamond Quality® Report is perfect for those that are not yet covered under the system. This grading report is also good for proprietary cut diamonds where the science of light performance has not yet recorded the ideal ratios for that cut shape.


Many in the diamond trade use proportion-based grading for evaluating the Round Brilliant diamond cut. AGS Laboratories developed a way to accommodate this preference for those who are not up to scratch with the AGS’s cut grading system. This is the AGS Laboratories Gold Diamond Quality® Report. By adapting the cut-grade technology from a three-dimensional system to a two-dimensional system, AGS is able to present their light performance evaluation in a proportion-based report for diamond cut. You get the science of the three-dimensional diamond cut grade with the familiarity and simplicity of the two-dimensional system for the Round Brilliant cut diamond.
The Gold Diamond Quality® Report is presented in a plastic sleeve with a front pocket, which contains a card with the diamond’s basic information. This makes it easy for jewelers to find the right diamond. This simplicity is the beauty of the Gold Report.

The AGS Diamond Quality® Analysis is yet another convenient pocket-sized document. This diamond report is for diamonds under 2 carats, so anything 1.99ct or under. The Diamond Quality® Analysis includes a complete grading evaluation of the 4Cs. The process of grading a diamond with the Diamond Quality Analysis includes inscribing the AGS number on the diamond by laser for identification. This report is used when a jeweler wants a cut grade document in a convenient smaller size.

  • AGS Scintillation Report

    The Scintillation Report is a unique and detailed report created by the American Gem Society Laboratories (AGSL). The AGSL has worked for years to refine the science behind a diamond’s sparkle. To arrive at the Scintillation Report, the AGSL had to perform hundreds of thousands of tests with different diamond cuts in varying lighting conditions.

    Ritani has partnered with AGSL in the creation of Scintillation Reports. This increases buyers’ confidence when choosing Ritani diamonds. Ritani uses the report to help them select round cut diamonds for their top diamonds called the Ritani Reserve diamond.


International Gemological Institute

  • IGI Diamond Report

    IGI Diamond Reports give an assessment of a diamond's cut, color, clarity and carat weight according to strict international standards. IGI Diamond Reports come in different formats and presentations to serve the diverse range of consumer demand across worldwide markets. Every report is issued according to the strict international standards and security features. IGI screens every diamond using state of the art technologies to determine naturally mined, laboratory grown or simulant origin. Experienced graduate gemologists conduct further assessment in controlled conditions, detailing relevant gemological characteristics according to the strictest international system. Any diamond with permanent treatments will have such treatments noted prominently in the comment section of the report. IGI does not issue reports for clarity enhanced diamonds.

  • IGI Hearts & Arrows Viewer

    Top H&A diamonds are valued for their uniqueness and quality as the ultimate in cutting precision. A percentage of well-cut diamonds, particularly near the center of the Excellent-Ideal range, show some level of cut precision, simply as a by-product of good tooling; what some cutters would call a ‘happy accident.’ Diamonds held to the uppermost level of craftsmanship will show extremely precise patterns. These exquisite diamonds are valued for the care, precision and consistency demonstrated in their cutting as much as any visible effects that result from this precision. There is also the attractiveness of rarity. Just as D color and Flawless clarity are rare, so is the H&A level of cut quality. The Hearts & Arrows viewer is a tool that helps gauge optical symmetry. Looking through it at the crown of a diamond you will see a pattern of arrows radiating outward in the crown of a H&A diamond. The hears pattern is visible once you turn the diamond over and view it through the pavilion. A circle of hearts can be seen in the pavilion. The arrows pattern may also be seen in certain lighting or under magnification when mounted but since diamonds are mounted with the pavilion down the H&A Viewer is the only way to see the hearts pattern. A diamond cutter must align all the facets perfectly for this to appear correctly. If any part of the diamond is even slightly off the patterns will be uneven or distorted and should not be considered a H&A diamond.

  • IGI Laboratory Grown Diamond Report

    Laboratory Grown diamonds, also known as lab grown, man-made, created or synthetic diamonds, are diamonds manufactured in a laboratory. This means they were not mined nor collected from an alluvial find. Natural diamonds are ones formed by naturally occurring processes within the Earth. The strong demand for industrial-quality diamonds, used in a variety of mechanical applications has been met in part by the development of laboratory grown diamonds. These have been manufactured for over half a century. In recent years technological advancements have made it possible to produce gem-quality laboratory grown diamonds of commercially significant size and weight. The IGI Laboratory Grown Diamond Report provides the same information as the IGI Diamond Report. Laboratory Grown Diamond Rep[orts issued by IGI can be easily spotted by their bright yellow color. The lab grown diamond's girdle is laser inscribed with the report number and the words "lab grown."