What Are the Ideal GIA Diamond Proportions? | Rare Carat

Saying there is an ideal GIA diamond proportion is like suggesting that there is a magic pair of jeans that fits you, and your mom and your uncle Charlie all at the same time.

Just like this ridiculous-sounding pair of jeans, in reality there is no ‘one size fits all’ ideal diamond proportion. This is because an ideal diamond is based on a delicate balance of all the different characteristics working together to provide the perfect environment for light to bounce around inside the stone. It is like a balance scales of sort, with the aim being to find the perfect (or ‘ideal’) balance between proportions.

Recipe for an Ideal Diamond

To put this another way, think of it like a recipe. Let’s say you are making a lemon pie, and the recipe calls for ½ cup of lemon juice but you drank too many eggnogs and mistakenly added ¾ cup. This pie is going to be much too sour. Not so fast! A little added sugar will cancel out that extra lemon in no time.

The same can be said for diamond proportions; a diamond with a shallow pavilion can be compensated for by a slightly steeper crown angle, or indeed vice versa. So rather than worry about a stationary ‘ideal’ number for each proportion, think of it like this instead.

There needs to be the right balance between all of the different proportions for a diamond’s cut to be ideal
All of the proportions (table size, crown height, etc.) have ideal ‘ranges’ rather than any one specific number, which leaves room for a balance to occur

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Rare Carat round diamond cut chart showing Rare Carat Ideal, Excellent, Very Good, Good, Fair, and Poor diamond cuts

We've made it easy. Go over the numbers, but when you go to search, just click on the Rare Carat Ideal filter, and it'll help you have all those ideal proportions set to search!

Table Size

Excellent to Poor - 52% to 62%
Very Good to Poor - 50% to 66%
Good to Poor - 47% to 69%
Fair to Poor - 44% to 72%
Poor - <44% to > 72%

Crown Angle

Excellent to Poor - 31.5° to 36.5°
Very Good to Poor - 26.5° to 38.5°
Good to Poor - 22.0° to 40.0°
Fair to Poor - 20.0° to 41.5°
Poor - <20.0° to > 41.5°

Pavilion Angle

Excellent to Poor - 40.6° to 41.8°
Very Good to Poor - 39.8° to 42.4°
Good to Poor - 38.8° to 43.0°
Fair to Poor - 37.4° to 44.0°
Poor - <37.4° to > 44.0°

Culet Size

Excellent to Poor - none to small
Very Good to Poor - none to medium
Good to Poor - none to large
Fair to Poor - none to very large
Poor - none to extremely large

Excellent to Poor - 45% to 65%
Very Good to Poor - 40% to 70%
Good to Poor - any value
Fair to Poor - any value
Poor - any value

Excellent to Poor - 70% to 85%
Very Good to Poor - 65% to 90%
Good to Poor - any value
Fair to Poor - any value
Poor - any value

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Diamond Proportion FAQs

What are some proportion ranges to look for if you want a diamond that sparkles well?

For a round brilliant cut, good ranges to aim for include a table size around 52‑62%, a crown angle between about 31.5° and 36.5%, and a pavilion angle roughly 40.6° to 41.8°. Also, a negligible or very small culet is preferable.

Can a well‑cut diamond with ideal proportions make up for other trade‑offs like a lower color or clarity grade?

Yes—a properly proportioned, well‑cut diamond often delivers more “live” sparkle and presence than a higher‑grade diamond that’s cut poorly. In many cases, the cut and proportions can matter more for the visible appearance than grading alone.

Does a cut graded “Excellent” always mean the diamond will sparkle its best?

Not always. Even such diamonds with poor proportions can cause light to leak out instead of reflecting back, resulting in little to no sparkle.

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Dr. Rian Mulcahy

Rian is officially a Diamond PhD - just ping us if you’d like to read her fascinating 200-page thesis, titled Facets of Value: An Investigation into the Formation of Worth in the Diamond Market. She has consulted various firms all along the pipeline, from the rough diamond market to the recycled diamond industry. She holds an MA in Globalisation and Development from University College Cork and a PhD in the Sociology of Diamond Valuation from the London School of Economics.