Ideal Proportions For Radiant Cut Diamonds

Q Hi, I’m looking at buying a radiant cut diamond (natural). What should I be looking out for? Do you have any tips for screening radiant cuts? Any help is appreciated.
-Jessie R.

A Hi, thanks for sending in your question. Radiant diamonds are a great choice if you love the shape of emerald cut diamonds but want something with a little more sparkle. In Fred Cueller’s excellent book How to Buy a Diamond: Insider Secrets for Getting Your Money’s Worth he states that the rule of thumb for choosing a great radiant cut diamond is called the 65/65 rule. That is a 65% table and a 65% depth. He goes on to say however that this is only a rough guide and there are other combinations that are equally appealing.

From the statistics I’ve seen, diamond cutters try to aim for certain attractive combinations which will sell well. In this post I am using those proportions as the middle of the road parameters when trying to identify the ideal proportions for radiant cut diamonds.

Just keep in mind that there are many variations among radiant cut diamonds that make a stone look fantastic.

The proportions of some beautiful looking radiant cut diamonds do fall outside of the range I state here. There are many variables which can be used when cutting a radiant diamond. So a cutter may produce a gorgeous jewel even though the crown height may be larger than stipulated here. I’ve seen great stones with a crown height of up to 20%. So just keep that in mind. However there are some basic guidelines which can help you find the best radiant cut which I will go over in this post.

So if you want some idea of where to begin your search here are some numbers you can start with:

Ideal Proportions for Radiant Cut Diamonds

Crown

Ideally the crown should be 10% or greater. 12% is a good average to aim for, but anywhere between 10% and 14% crown height is fine. You will rarely see the crown height listed on a diamond’s grading report so you will either have to request that information from the dealer or get a rough calculation from an image if you can get a nice clean and non-distorted profile shot. Below is an example of what a radiant cut diamond with a 12% crown height looks like.

Table

The ideal table size for a radiant cut diamond may lie anywhere between 64% and 68%. Many diamond experts agree that a 65% table size is ideal for radiant cut diamonds. This is one parameter that is included on diamond grading reports and is also something that can usually be entered in when conducting a search.

Here is a lineup of radiant cut diamonds with a 65% table.

Depth

The rule of thumb for radiants was once said to be 65/65: 65% table and 65% depth. There was even a special term for these stones: flagship. However this rule of thumb should only be taken as a rough guide. I recommend including depths up to 70% in your search. So anywhere between 65% and 70% depth can yield a beautiful result.

Here is a lineup of “flagship” radiant cut diamonds: a 65% table and a depth of 65%.

Sometime however you will come across a radiant cut diamond that looks great in spite of having a depth percentage greater than the range I have stated above. The main disadvantage to be aware of is that a deeper cut, that is a greater depth percentage will result in a loss of spread.

Here are a few radiant cut diamonds with a depth percentage of 75%

Let’s take a closer look at the top left diamond which is a 1.02 Carat F VS1. This stone stood out to me, and I think you will agree with me that it is a beautiful stone.

It’s a great example as to how there can be exceptions to the rules, and why it’s important to not get hung up on parameters which are too narrow. The table on this stone is 57.5%. This is considerably smaller than the industry standard for radiant cut diamonds. But it works.

Here is the stone in profile:

It has a crown height of 29%. That’s a far cry from the 10% to 14% often cited as the ideal. Yet the combination works very well.

Length to Width Ratio

Many people prefer a radiant cut diamond to have a 1.25:1 length to width ratio. Radiant cut diamonds though come in all sorts of ratios and it comes down to personal preference. Some want a slightly longer diamond and therefore look for a radiant cut diamond with a 1.40:1 length to width ratio, or even greater.

Following are the two commonly sought after length to width ratios:

Some people look for a square radiant, something closer to a 1:1 length to width ratio as they may like the fact that this is half way between a princess and cushion cut. This way they get the benefit of the square look of the princess cut without the sharp and vulnerable corners.

Send in your question

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As an affiliate of the some of the world’s finest jewelers I am motivated to find the right purchase that is perfect just for you. Every person has specific needs and every jeweler has specific areas in which they excel.

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Thomas J Stevens GIA DG CSG

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