AGS Ideal Cut vs. GIA Excellent Cut Diamonds (Which Is More Important)

Diamonds — a durable gem that comes in every color in the rainbow — are a huge investment. Because of that, most people in the market for a diamond want to make sure they make the right choice, especially if you’re considering an American Gem Society (AGS) ideal cut versus a Gemological Institute of America excellent cut diamond. Even though these two certifications can seem confusing, they’re both equally interesting and important to learn about.

Although both the AGS ideal cut and the GIA excellent cut are solid choices when considering buying diamonds, the AGS ideal cut is usually the preferred diamond for customers and jewelry experts. Still, that doesn’t mean GIA excellent cut diamonds should be overlooked; the GIA is a well-known, respected agency.

Luckily, deciphering the differences and similarities between the two certifications doesn’t have to be overwhelming. In our guide, we’ll break down the main differences between the two grades — the AGS ideal cut and the GIA excellent cut — as well as the ways in which they’re similar.

We’ll also answer another burning question: Should the AGS ideal cut versus the GIA excellent cut impact your purchasing decisions?

AGS versus GIA

There are two primary organizations that deal with all things gemstone: the American Gem Society (AGS) and the Gemological Institute of America (GIA).

Although they’re very similar in mission, there are a few important differences between the two.

In the 1930s, the American Gem Society was founded by a group of motivated, respected jewelers, including a man named Robert Shipley. The original goal of the AGS was to ensure that people buying jewelry were protected from and informed of both false advertising and fraud.

Today, the AGS is comprised of thousands of suppliers, jewelry experts, and retailers who carry on that same mission: the protection of customers and the education of gemological knowledge and techniques.

Still, not everyone can become a member; in fact, only 1 in 20 jewelry professionals will meet the requirements. It’s a rigorous process that includes passing an annual recertification exam as well as a peer-reviewed application process.

The Gemological Institute of America is an organization also established in the 1930s by ​​Robert Shipley. About 10 years later, the GIA put together the guidelines for the international diamond grading system and the four C’s: cut, clarity, carat weight, and color. The world uses this technique even today in order to grade diamond quality.

Since its creation, the researchers at the GIA have put much effort into gemology and educating people about gemstones.

Both these organizations use certain characteristics — from brilliance to symmetry —  to grade gems.

Characteristics Graded by AGS Ideal Cut and GIA Excellent Cut

There are four primary characteristics that are graded by the AGS ideal cut and the GIA excellent cut: symmetry, brilliance, fire, and polish.


Diamond symmetry grades are a critical part of analyzing gems. In this context, symmetry is how precise the degree that the facets intersect with each other. The more precise, the better. When evaluating the gem’s symmetry, the process could include looking at aspects like off-center culets or tables; wavy girdles; or misshapen and even extra facets.

Although there’s something called “optical precision” or “optical symmetry,” this isn’t important in this case, as the AGS ideal and the GIA excellent cuts don’t include that degree of precision in their evaluations.


Brilliance is an incredibly important (and very noticeable) aspect of diamond grading for both the AGS ideal and the GIA excellent grade cuts. Brilliance in a diamond is defined by the amount of white light that’s reflected in a diamond. For example, the more reflected light a diamond has, the more brilliance it has. Brilliance is the aspect responsible for a sparkling, shining diamond.

Higher quality diamonds — including the AGS ideal and the GIA excellent cuts — are going to have a higher level of brilliance.


Fire is similar to brilliance in that it’s related to light. However, fire is more focused on how the diamond sparkles. You can think of fire and brilliance as cousins: they both refer to how light is reflected or emitted. So, for example, an AGS ideal or GIA excellent cut will have a higher fire grade. In general, round cut, brilliant diamonds will have a higher fire grade than other cuts.

The light should disperse into many colors, like a rainbow. Well-cut diamonds shouldn’t lack in color where light is reflected.


A diamond’s polish refers to how smooth the gem is. A gemologist or other expert will measure how smooth each facet of the gemstone is, as well as evaluate the diamond for any imperfections.

As you can expect, both the AGS ideal and GIA excellent grade cuts will have an impressive polish. However, it’s possible that the person evaluating the gem will find imperfections.

The cut and polishing process — as well as the person doing the cutting and polishing — could be to blame. Unfortunately, tiny, microscopic blemishes could affect a gem’s polish. These defects happen when the wheel that polishes the diamond dislodges small crystals and inadvertently drags them across the gem’s surface. If the damage is extensive, the improper polish could negatively affect the light reflection and thus, the brilliance and fire.

All of these factors are extremely important when determining the AGS ideal or GIA excellent grade cut diamonds. But how do the two cuts compare?

AGS Ideal Cut versus GIA Excellent Cut

The AGS ideal or GIA excellent grade cut diamonds are both impressive, certified cuts. As they were created by the same group of jewelers, the AGS and GIA cuts are each similar and different in their respective ways.

AGS Ideal Cut

In 1996, the AGS began proportion-based grading. This was based on the proportions of Belgian engineering student Marcel Tolkowsky, who was from a respected family of talented diamond cutters.

Tolkowsky gets the credit for creating the so-called “American Ideal Cut.” Before Tolkowsky, it wasn’t until the early 1900s that people began evaluating diamonds on other factors; before then, the early guidelines were solely based more on cosmetic features instead of scientific evaluation. In 1955, the most up-to-date version was deemed the “AGS Ideal Cut.”

The AGS evaluates and grades diamond cuts based on a 0 to 10 scale. The ideal cut would be 0, where 10 would be ranked “poor.” These scores are based on the AGS’ standards for diamond cuts and the scores also have verbal descriptors: poor, fair, good, very good, excellent, and of course, ideal.

However, today’s AGS grading system went into effect on June 1, 2005, meaning if you had a diamond with an AGS ideal cut ranked 0, it might not be ranked 0 or ideal based on the current system. 

In terms of AGS cut grading, any cut that’s ranked 8 to 10 is considered poor. Fair cuts are associated with grades from 5 to 7. Cuts that are considered good have a numerical value of 3 or 4, while a ranking of 2 is very good. Last but certainly not least, we have excellent cuts, which include both 1 and 0, the latter being ideal.

The AGS ideal cuts are extremely desired thanks to their brilliance, symmetry, fire, and polish. These cuts have more sparkle, more color, and a better clarity than lesser cuts and make for some very fine jewelry. In fact, when comparing diamonds, if you’re looking at a larger but poorly cut diamond next to an ideal, small diamond, the small diamond might actually look bigger, only due to its quality.

Because the AGS ideal cut represents only the most quality cut gems, be wary of jewelers that tell you a diamond is an ideal cut; it’s only a true ideal if it’s AGS-certified.

GIA Excellent Cut

The GIA is responsible for creating the four C’s system of diamond evaluation which was initiated in the early ’50s. Because of this, diamonds are appraised by cut, color, clarity, and carat weight. The current GIA grading system was put into motion in 2005. Researchers with the GIA conducted around 70,000 observation tests and used the results to create their cut grading system.

With the GIA cut grading system, there are five diamond cut grades: poor, fair, good, very good, and excellent. For example, a poor grade diamond cut isn’t a popular choice due to the fact that it’ll usually have noticeable dullness or even dark areas in the gem.

The system that the GIA uses also penalizes any diamond with deep pavilions, steep crowns, or extra weight from girdles that are too thick.

A diamond that has a good cut grade is a step or two up from poor. These gems will usually have some darkness or dullness but are not as noticeable as a poor or fair diamond. Good cut grade gems have less brightness since light reflections won’t be as crisp.

Finally, we have the excellent cut grade diamond. These gems have sharp, balanced reflections that boost their brilliance, making them a dazzling spectacle. GIA excellent cut diamonds also have a proper light-to-dark area contrast with an even pattern.

A GIA excellent cut diamond ensures an attractive, sparkling diamond you can depend on. The brilliance reflects its impressive grade through the internal and external white light reflections, making it a brighter gem compared to a poor grade cut diamond.

In a similar vein, excellent cut diamonds exude a noticeable fire, meaning all the colors of the rainbow shine brightly due to the light that travels through the diamond. A poorer diamond would have trouble reflecting light in such a way.

GIA excellent cut diamonds also have an impressive scintillation — that is, sparkle and pattern — that assists the light reflection. The pattern and its contrast give it a sharp, crisp aesthetic.

All of these factors combined make GIA excellent cut diamonds extra desirable.

Though we already know these two cuts are two sides of the same coin, many people interested in diamonds wonder which cut is better.

Which Is Better: AGS Ideal Cut or GIA Excellent Cut?

We know both the AGS ideal cut and the GIA excellent cut diamonds are the best of the best. But which is the better choice?

The AGS is a pioneer in the world of fine, high quality diamonds. With the AGS, its diamond grade cut system is extremely specific. The way in which they analyze diamonds is pretty extensive, and their diamond evaluation system is currently the sole diamond grading system that’s backed up by science.

Of the majority of laboratories, this organization has the more thorough evaluation. That being said, many customers and diamond professionals prefer the AGS ideal cut diamond when shopping for a gem.

However, the GIA has a more general, almost lenient cut grading system. Even so, it’s often considered the most trusted of laboratories. It’s a popular agency, especially since the GIA is responsible for creating the infamous four C’s — cut, color, clarity, and carat weight — diamond grading system. The GIA is a truly valued entity.

While the AGS ideal cut is generally more preferred by customers and diamond professionals everywhere, the GIA excellent cut is well-respected and a trusted source for high quality diamonds.

Still, you truly could not go wrong when deciding between the AGS ideal cut and the GIA excellent cut. Both the GIA and the AGS were established by the exact same jewelry experts, so each is worth considering.

That being said, it’s important not to forget to factor in diamond cost when comparing the two.

Pricing of AGS Ideal Cut versus GIA Excellent Cut

Diamonds are usually priced out by a number of factors, such as their color, clarity, their carat weight, and of course, their cut. When it comes to the AGS and the GIA, those certificates could potentially make the cost higher or lower, depending, but in general, they’re going to have pretty similar prices.

Although some people say that AGS ideal cut diamonds sell for up to 10% more than the GIA diamond equivalent, the general consensus is that these certifications don’t make a diamond more expensive.

In fact, the AGS doesn’t have an interest when it comes to diamond sales. Thus, diamonds that are certified by the GIA will cost very similarly to diamonds certified by AGS.

At any rate, your decision to choose the AGS over the GIA diamond cuts will most likely come from the other aforementioned factors. You


The AGS and the GIA certificates are well-respected, distinguished authentication for high quality cut diamonds.

Both the AGS and the GIA were founded by the same group of jewelry professionals, so they do have some foundational similarities. However, while the AGS certification is more specific and uses both numerical and verbal descriptors, the GIA usually tends to use verbal descriptors, and its grading scale is broader.

They’re both going to cost about the same price at the end of the day, although some experts argue that AGS could cost you more. You may want to check our TW diamond buyers’ guide.

Either way, ultimately, you can’t go wrong with the AGS ideal cut and the GIA excellent cut diamonds.