Ideal cut is a concept that is of utmost importance when deciding what kind of diamond to buy. But what exactly are the standards for ideal diamond cut, and what measurements should a stone have in order to be close to the ideal?
The Meaning of Ideal Cut
When referring to round-cut diamonds, a cut is considered ideal if its proportions allow the stone to retain and reflect as much light as possible back to the eye of the observer, maximizing the brilliance and sparkle of the diamond.
On the other hand, the further a diamond’s proportions are from the measurements that are considered ideal, the more of the light that enters the stone leaks out of it.
Since the facets of poorly cut diamonds are not well aligned to retain maximum light, such stones appear dull and lifeless.
Different Ideal Cut Standards
Although it may seem that the definition of ideal cut is uniform, there is actually no universal agreement as to what the exact ideal proportions should be.
In reality, there are at least half a dozen standards for the measurements of the ideal cut.
The most widely used benchmarks today are the American Standard, the Practical Fine Cut, and the Scandinavian Standard.
The first one is used in North America, and the other two are mainly used in Europe.
Ideal Cut Proportions
Although there are different standards for ideal cut, the proportions they use as guidelines do not differ significantly in value.
The first thing you should know about the ideal measurements is that they are expressed as percentages of the diameter of the diamond’s girdle, which is simply the stone’s edge and is also its widest part.
Let’s look at the most important measurements of an ideal-cut diamond. The numbers are given as ranges that include the standards of the most widely used benchmarks:
Table diameter: 53%-57.5% (This is the diameter of the diamond’s flat top, i.e. the table.)
Crown height: 14.4%-16.2% (This is the vertical distance from the girdle to the top of the stone; the crown is the upper part of the diamond, from the girdle to the table.)
Pavilion depth: 43.1%-43.2% (This is the vertical distance from the girdle to the bottom of the diamond; the pavilion is the lower part of the diamond, from the girdle to the lowest point.)
So, using the above numbers to derive a rule-of-thumb benchmark, we can conclude that an ideal-cut diamond should have a top that has a width of 53% to 57% of the girdle, a pavilion that is around 43% deep, and a crown that is around 14.5%-16% high.
The total height of an ideal diamond, measured from its flat top to the stone’s pointed bottom, will be around 60%, give or take 2-3 percentage points.
If you are shopping for a diamond, you most likely won’t need to measure all these values yourself: They will be included in the diamond’s grading report, and you should look them up. It is not recommended to buy diamonds that do not come with such a certificate that verifies their quality.
The Diamond Cut Grading Scale: A Shortcut to Evaluation
You don’t necessarily need to examine the abovementioned measurements in detail for each stone you are looking at.
Luckily, the G.I.A. (Gemological Institute of America) does the job for you, and by taking into account a variety of standards for lengths and angles, it assigns a cut grade to each diamond it certifies.
If the diamond you are considering comes with a G.I.A. grading report, take a look at it.
The G.I.A. grades cut using the following categories: Excellent, Very Good, Good, Fair and Poor.
In general, anything that is graded Good and higher is a fine option. Avoid diamonds graded Poor; those with a Fair cut are of so-so quality, so it’s up to you to decide whether such a stone is worth it.