What’s the Best Diamond Cut for Engagement Rings?

The cut of the diamond is the most important of the 4 Cs because diamond cut is what determines the brilliance of a diamond. With diamonds, it begins with learning about the 4 Cs of diamonds – diamond cut, diamond clarity, diamond color, and diamond carat.

The brilliance also refers to the diamond’s sparkle, which is the most important aspect of a diamond to consider (not the size of it! That’s right, I am telling you size doesn’t matter). This article will provide you with everything you need to know about diamond cut, but if you are short on time, here are the most important things you need to know:

  • Most people believe that diamond cut is a reference to the diamond shape (round cut, princess cut). This is NOT TRUE. The diamond cut is a reference to how well-proportioned and symmetrical a diamond’s facets and angels are, which determine the diamond’s brilliance
  • Does your diamond have enough fire in it? Fire is the rainbow colored sparkle you can see when the diamond is in light. You can see more fire in a diamond in darker rooms that have fewer light sources
  • Does the diamond exhibit proper scintillation? Scintillation is the sparkle a diamond exhibits as it moves. You can see more scintillation in strongly-lit rooms,
  • The diamond should exhibit a proper amount of BRILLIANCE. If a diamond has proper proportions and symmetry, more light will reflect back from the diamond which will make the diamond look more brilliant or sparkly. Brilliance is strongest in diamonds that exhibit both fire and scintillation.
  • The diamond you buy should be “eye clean”. Eye-clean is an unofficial term used to describe a diamond whose inclusions cannot be seen with the naked eye (20/20 vision), 6-12 inches away from you viewed face up in daylight (or fluorescent lighting).

You don’t need to overwhelm yourself with becoming an expert on buying diamonds – it’s not worth investing the limited time you have for one purchase; so feel free to stop reading about diamond cut here. But, if you really want to learn more about diamond cut, check out the rest of the article below.


What is Diamond Cut?

As mentioned above, a diamond’s cut, which is the main factor that determines the diamond’s brilliance or sparkle, will tell you how well-proportioned a diamond is. So how sparkly should your diamond be? There really is no right answer to this, but you want to make sure that light going into the diamond reflects back out from the diamond. If you’re looking at a diamond and you see a sparkle and notice colors of the rainbow, you’ve likely got a well-cut diamond on your hands (<- That’s a good back of the envelope way of assessing diamond cut). However, for jewelers who have trained eyes, they consider many other qualities when assessing the quality of a diamond’s cut, some of which are below:

  • How well-proportioned is the diamond?
  • Are the facets symmetrical or are there places where it is out of balance?
  • How is the polish of the diamond?

Let’s go into more detail regarding all of these topics.


Diamond Proportions

As you evaluate a diamond cut for yourself, you will want to consider the following elements:

  • Diamond Table – The length of the top of the diamond
  • Diamond Width – The overall diameter of the diamond.
  • Diamond Depth – How tall it is from top to bottomDiamond Proportion Diagram

Diamond Table

The diamond table is the top part of the diamond which light enters through. Literally think of a table when trying to conceptualize (i.e. what part of the diamond would you be able to place your dinner on? The top of the table right?) Now look at your diamond – yes, that the table.

Why does the diamond table matter? Well if your table is too small, less light will be able to enter the diamond, decreasing its brilliance. But if it is too large, then light won’t be able to disperse as much which will affect its fire, and you won’t have the sparkle you’d ideally like. Keep in mind that you can’t just look at the size of the table alone, you need to look at it in relation to the width of the diamond, which will give you the table %.

Table % = Diamond Table / Diamond Width

Ideally, your diamond falls within an acceptable range in terms of the table %, which is highly dependent upon the overall shape of the diamond. Look at the benchmarks below:

You want to evaluate the length/width ratio to see how proportionate the diamond is, which also factors into determining its brilliance. The ideal length/width ratio varies depending on the shape of the diamond. For a well-proportioned diamond, you want the length/width ratio to be in the following ranges:You still need to consider the other elements that create the overall form of your diamond. Let’s look at the width next.

Diamond Width

The width of a diamond is determined by measuring the distance from one end of the girdle to the other. Girdle is the thin area of a diamond which breaks up the crown from the pavilion. When you’re looking at a diamond in its profile view, as in the diagram above, it’s the widest part of the diamond (above, the width = girdle). The length of the diamond is measured by looking at the diamond from the face, or the top view. It is the longer of the two top to bottom distances.

Length/Width Ratio = Diamond Length / Diamond Width

Ratio RangeDiamond Shape Ideal L/W
Round Cut 1.00 : 1.00
Princess Cut1.00 - 1.05 : 1.00
Cushion Cut 1.00 - 1.20 : 1.00
Marquise Cut 1.95 - 2.05 : 1.00
Oval Cut 1.45 - 1.55 : 1.00
Pear Shape 1.55 - 1.65 : 1.00
Heart Shape 1.00 - 1.05 : 1.00
Radiant Cut 1.00 - 1.20 : 1.00
Emerald Cut 1.35 - 1.55 : 1.00
Assher Cut 1.00 - 1.05 : 1.00

Diamond Depth

Depth is the term used to refer to the overall height of the diamond from the culet (the pointed end) at the bottom to the table at the top. On its own, depth has little relevance, but in relation to the width, it helps determine if there is enough opportunity for light entering through the table to get to the bottom and reflect around to the upper facets.

Diamond Depth / Diamond Width = Depth %

If the depth is too little, then it will have an impact on the interaction between the white light and the colored light. If the depth is too much, then it will cause the diamond to have less brightness showing out. The ideal depth % for a diamond varies with its shape. Below is a table of the ideal depth % below.

Diamond Shape Ideal Depth % (Range)

Round Cut 59.0% – 61.0%

Princess Cut 60.0% – 75.0%

Cushion Cut 59.0% – 65.0%

Marquise Cut 56.0% – 72.0%

Oval Cut 56.0% – 65.0%

Pear Shape 56.0% – 65.0%

Heart Shape 56.0% – 65.0%

Radiant Cut 60.0% – 63.0%

Emerald Cut 60.0% – 63.0%

Assher Cut 59.0% – 65.0%

Why do proportions matter?

If the diamond table, width, and depth are out of proportion, then you will not get the proper reflection of light off the diamond’s facets and it will impact the overall brilliance of the diamond. Usually, if the proportions are off, it indicates that the diamond cut is either too shallow or too deep.

What happens if your diamond cut is too shallow?

If you are looking at a diamond with a cut that is too shallow, you will see that when light comes through the table will end up exiting through the sides, instead of reflecting back up through the table; thus reducing the brilliance, fire, and scintillation.

What happens if your diamond cut is too deep?

When the cut is too deep, light that comes in through the table pass through the bottom of the diamond, instead of reflecting back up through the table, which will also reduce in a less brilliance.

So what is an ideal proportioned diamond?

When you have a well-proportioned diamond, in terms of table %, length/width ratio, and depth %, light coming in will reflect back up and out through the table. When this happens, the diamond will appear to show greater brilliance, fire, and scintillation.

Diamond Symmetry

The symmetry of a diamond refers to how symmetric the facets of a diamond are or how well aligned the angles are. Basically, the better the symmetry, the greater chance light has to reflect back up through the table, which improves brilliance. There is no way for a regular consumer to gauge symmetry of a diamond by looking at it, so it’s important to rely on the grading provided by a major grading agency. GIA and AGS are the two most widely used grading agencies (more below). We believe that a grading of good or better is an indication of a symmetric diamond.

Diamond Polish

Diamond Polish refers to how smooth the outside surface of a diamond is. Again, this is tough for a normal consumer to gauge, so you want to rely on the grading provided by one of the grading agencies. A diamond with an Excellent or Ideal Polish will have a very smooth surface which allows for the most light to come in and reflect back, resulting in greater brilliance, fire and scintillation. A diamond that has been polished poorly will let less light in through the table, which will negatively affect the diamond’s luster and brilliance.

Grading Agencies

The two grading agencies that are most widely used are GIA and AGS. Is one agency better than the other? No, the choice of one lab over the other will is based on the manufacturer and what deal they can get from which agency though GIA is more widely used than AGS.

• GIA: The Gemological Institute of America is an independent nonprofit that protects the gem and jewelry buying public through research, education and laboratory services. Btw, keep in mind that GIA only provides an overall cut grade on standard round brilliant diamonds. In my opinion, stay above a GIA cut grade of Good.

o Excellent- An Excellent cut diamond provides the best interaction between color and white light in a diamond (brilliance, fire, and scintillation). In this kind of diamond, almost all of the light is reflected out of the table.

o Very Good- a Very Good cut diamond will still have good brilliance, fire, and scintillation, but not quite as good as an Excellent cut diamond. But to the naked eye, there will be little difference between Excellent and Very Good. However, the price difference will be noticeable

o Good- With a diamond with a Good cut, you will still get great value, but you will notice the difference in brilliance versus a Very Good cut diamond just by looking at the diamond with your naked eye.

o Fair- A Fair cut diamond will have little brilliance because the light reflecting back from the pavilion will mostly exit from the bottom of the diamond leaving little reflected light to captivate the eyes.

o Poor- A Poor cut diamond will provide little or no light because the improper design allows almost all of the light to exit at the bottom of the diamond.

• AGS: The American Gem Society is the country’s preeminent jewelry trade organization dedicated to consumer protection. AGS provides an overall cut grade for almost all diamond shapes on a scale of 1-10, along with grading indications (e.g. ideal, excellent, etc). The table below shows how the GIA grading system correlates to the AGS number scale. Stay above an AGS cut grade of Very Good.

GIA Cut Grades AGS Cut Grades

Excellent Ideal (Grade 0)

Very Good Excellent (Grade 1)

Good Very Good (Grade 2)

Fair Good (Grade 3-4)

Poor Fair (Grade 5-7)

Poor (Grade 8-10)

How does the Cut Grade of your diamond help to determine its price?

You will find that the better the cut grade, the higher the price because of the quality and beauty of that particular diamond. You will benefit more from higher cut grade as it will have a greater amount of brilliance and fire making your diamond more appealing to those looking at it.

PHD Bottom Line

Remember, a diamond’s quality is based on how the light plays around inside the diamond. The best diamonds have a large amount of brilliance, fire, and scintillation allowing for the greatest reflection of light. You also want to focus on the proportions, symmetry, and polish of the diamond. Check out how the table, width, and depth interact with each other to create brilliance and fire. Is the shape symmetrical or is it out of balance? How well is the outer surface of the diamond polished? Hopefully, we provided you with all the information you need to know about diamond cut. Good luck with the shopping!