Diamond Girdle Thickness And Why It Is Important

A diamond’s outermost edge is also known as the girdle. This thickness is measured as a percentage of the diameter (e.g. thin = 1.0%, medium = 3.0%, thick = 4.0% etc…) or described using words (such as Medium, Thick or Thin).

In a grading report, the finish of the girdle will also be stated and listed as one of the following: polished, faceted or bruted. This information can be found in the proportions diagram that looks like the example below.

profile proportions

Want a fast track to the ideal diamond proportions to look out for when shopping for an engagement ring? Click here to view a chart showing the best proportions for buying well cut round diamonds.

Why is the Diamond’s Girdle Thickness Important?

First of all, the ideal girdle thickness should not be too thin such that it causes a heightened risk of chipping. On the other hand, the girdle thickness shouldn’t be too thick as it will result in “dead weight” which makes the diamond appear smaller.

You should also beware of diamonds with extreme girdle thickness variations (e.g. very thin – extremely thick) as they usually indicate symmetry issues and poor cut. Besides lower optical performance, extreme variations can also cause problems during the setting process.


If the girdle thickness is extremely thin, the facets junctions of the crown and pavilion facets meet together to form a knife edge. From a mechanical perspective, the diamond’s crystalline structure is weakest at knife edges and makes them very susceptible to damage.

knife edged girdle that is chipped

In the photograph above, the knife-edge girdle has nicks and chipping damage.

The finishing of the girdle may also create undesirable appearances for the diamond. For example, if a bruted girdle is sufficiently thick enough, it can cause an unsightly gray reflection to appear under the table facet.

As a general guideline, I only recommend buying diamonds with polished or faceted girdle finishing.

Diamond Girdle Size Chart Reference

diamond girdle thickness chart

I only recommend buying diamonds with grading certificates from GIA or AGS. Besides a reliable grading report, White Flash and James Allen also provides additional information like ASET/Idealscope images and magnified videos to help you make better decisions.

Here is a List of Acronyms Commonly Used

Girdle thickness is classified into categories ranging from extremely thin to extremely thick. Diamonds with girdles that lie in the outer regions of extremely thick and extremely thin have cut related issues in them. This is one of the reasons why such stones are usually less valuable and sell for a lot less.

  • Extremely Thin – ETN, ETH, XTN, EXN
  • Very Thin – VTN, VT, VETN
  • Thin – T, TN, TH
  • Medium – M, ME, MD, MED
  • Slightly Thick – STK, ST, SLTK, SLTH
  • Thick – T, TK, TH
  • Very Thick – VTK, VTH
  • Extremely Thick – ET, EXTK, XT, XTK
  • Faceted – F, FA, FAC
  • Smooth – S, SM

How is Girdle Thickness Described on a Grading Report?

The gemological labs assign a description based on the thickest and thinnest portions of the girdle. Also, it’s common to see variations in girdle thickness across a diamond instead of a nice uniform thickness throughout the diameter.

slightly thick to very thick

Slightly Thick – Very Thick

very thin to thick

Very Thin – Thick

The above examples present 2 round brilliant cuts with different problems. The diamond on the left has weight retained at the girdle area and results in a smaller looking diamond from the face up view. The one on the right poses a serious durability problem due to the very thin section of the girdle.

Also, just by looking at these profile views, you can actually deduce that these diamonds have problems with their overall symmetry.

Comparison of 1 Carat Diamonds With Uniform Girdle Thickness

extremely thick girdle retains weight

Ex. Thick – Measurement: 6.00 * 6.06 * 4.14 mm

uniformly medium girdle size in round diamond

Medium – Measurement: 6.49 * 6.47 * 3.94 mm

An extremely thick girdle causes excessive weight retention which is hidden from sight after mounting. This is also one of the reasons why 2 stones with similar carat weight can face up completely different and have stark physical dimensions from each other.

Did you know that GIA’s grading system will penalize and downgrade the diamond’s cut rating because of the girdle thickness it has? Using the 2 examples above as references, the cut grade of the diamond on the left was graded as Fair while the one on the right received an excellent rating.

the gia cut grade relationship

Note: This table is only applicable for round diamonds. Source: Culet And Girdle Assessment, GIA

Situations Where a Thick Girdle May Be Preferred

It is perfectly OK for diamond shapes such as the heart, pear or marquise to have thicker girdle thicknesses at the locations of the pointed edges. In this case, the extra thickness provides additional strength and acts as a form of protection against chipping.

acceptable variances in fancy shapes

marquise with 2 pointed corners

The girdle thickness increases near the tips of this marquise shaped diamond.

Summary: What I Would Personally Buy And Recommend

I know many people get hung up on finding a diamond with a “perfect” girdle when there’s actually no need to overthink stuff. So, here’s the bottomline when it comes to girdle thickness?

For round brilliant cut diamonds, you should only buy diamonds within the range of thin – medium – slightly thick girdles. That is to say, if you see a round diamond with a thin – slightly thick girdle, that’s perfectly fine. Likewise, if you see a thin – medium or medium – slightly thick girdle, that’s OK too!

For fancy shape diamonds, a girdle range of thin – medium – slightly thick – very thick would be recommended. I need to emphasize that it is alright to buy a fancy shape diamond with a very thick girdle as long as it is well cut.

At the end of the day, the girdle thickness is just a small aspect of choosing a well cut diamond. The more important things you should look out for when choosing a diamond is tangible data that determines cut quality and light performance.

If you are shopping for an engagement ring, James Allen and White Flash are the best places I recommend. Not only do they offer videos and images to help you make analytical decisions, they also have a great selection of beautiful ring settings to choose from.

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  1. Avatar
    July 14, 2013 at 8:16 am

    I had been browsing diamonds online for quite some time now and intend to buy one in the next few weeks. During my research, I had noticed many diamonds exhibit girdle thickness that seem to vary quite wildly from each other.

    For example, thin – medium girdle thicknesses are typically seen in round diamonds. We see a larger fluctuation in fancy cuts such as thin – extremely thick, medium – slightly thick, thick – extremely thick, thin to very thick and the list goes on for girdle thicknesses.

    I had read in your article on diamond girdle sizes and you mentioned that medium is the one we should go for. Based on my fiancé’s preferences, I had been looking at some fancy cuts lately and had seen some pretty nice ones at James Allen. However, the concern I have is that some of these shortlisted diamonds have girdle thickness from thin – very thick or medium – extremely thick.

    Should I discount these diamonds and only select those with a medium girdle?

  2. Avatar
    Paul Gian-
    July 15, 2013 at 11:44 pm

    Hi Dreamer,

    You had raised quite a number of points here and I will attempt to answer them one by one. Typically, I would avoid diamonds with an extremely thick girdle as there is a possibility the girdle can act as an extra facet of sorts. In poorly cut diamond, this can alter the diamond’s appearance in a way which is unpleasant and distracting to look at.

    Next, if a diamond has a uniform girdle of ‘extremely thick’, I would advise you to avoid them. Such diamonds are overweight and you are basically paying for the “dead weight” that you can’t see once it is mounted.

    For fancy cuts, if a diamond exhibits a girdle of medium – extremely thick, I wouldn’t avoid it ‘per se’ without knowing the rest of the diamond’s properties. This should be determined on a case to case basis.


    girdle thickness issues

    Basically, the girdle is measured around the entire circumference of the diamond. The thinnest and thickest areas will be listed in the grading report. In the example above, the girdle of the diamond is ‘medium’ at its thinnest point, and ‘extremely thick’ at its thickest point.

    Now, I wouldn’t totally write off a diamond in this case as it might not be detrimental to the stone’s outlook. You will need further data like ASET images and videos to determine whether it is a keeper.

    I would however, always avoid diamonds that fall under these scenarios:

    1) Any mention of Extremely Thin.
    2) A uniform girdle thickness of Extremely Thick.
    3) Huge deviations like Very Thin – Extremely Thick.

    Hope this helps clarify things,

    ps. when searching for fancy shaped diamonds, the odds are against you to buying a well-cut diamond. You need every tool at your disposal to make the best possible choices and I highly recommend JamesAllen.com because you can see exactly how the diamond looks like with their video technology. On top of that, they are able to perform gemological evaluations like light performance and capture ASET imagery on your behalf.

  3. Avatar
    August 31, 2016 at 2:22 am

    I’m so sorry I can’t seem to locate my last comment/question. I also wanted to see your thoughts on this diamond? Based on the dimensions will it appear larger than actual size. Is this a fair price, $17,500? Is the slightly thick faceted diamond any problem at all?


  4. Avatar
    Paul Gian-
    August 31, 2016 at 2:29 am

    There’s no way I can offer constructive feedback on a fancy cut oval diamond based on the grading report alone.

    Read these in full:

  5. Avatar
    September 29, 2016 at 1:29 am

    What do you think about lab created diamonds at brilliantearth.com. Are they really optically, physically and chemically identical to earth mined diamonds? I was looking at https://beyond4cs.com/go/be-2718170/ and https://beyond4cs.com/go/be-2719148/

    This second ones girdle is faceted. Would the second one be better? I spoke with my girlfriend and after reading about lab created diamonds she said that she would be okay with it.

  6. Avatar
    Paul Gian-
    September 29, 2016 at 4:20 am

    Read this: https://beyond4cs.com/grading/girdle-thickness/does-finishing-matter/

    By proportions alone, this would be the better diamond on paper.

  7. Avatar
    Mohamed Salama-
    November 2, 2016 at 4:24 pm

    Hi Paul,

    When a diamond has a girdle thickness in the GIA report as medium to slightly thick (faceted) 4.0%

    What does the % here mean?

    Does the 4% here indicate the % at the slightly thick part of the girdle?

    Why is there a single % number? Shouldn’t there be one for the medium and one for the slightly thick?

    I read this http://diamondcut.gia.edu/pdfs/booklet_finish_culet_girdle.pdf

    It talks about the % in general and how it is calculated. I don’t know what it means to have one number only.

    Can you please help?

    Thanks alot!

  8. Avatar
    Paul Gian-
    November 3, 2016 at 4:37 am

    Girdle thickness percentage = total depth % – (crown height % + pavilion depth %)

  9. Avatar
    September 7, 2017 at 5:33 pm

    Hi Paul – Appreciate all the content on what girdle is best for diamond. It’s been a huge help. I’m having a hard time finding out why the two listed below have a price difference. They are pretty much the same thing in terms of varying categories, details are below.

    Would really like your take on these two…


    1.56 Carats
    Polish – Very Good
    Symmetry – Very Good
    Flour – None
    Price – $14.7K
    Depth – 64 (excellent 64 is perfect)
    Table – 70 (very good)
    Length to width – 1.12 (very good for a rectangle cut)
    Girdle – Very Thick to Extremely Thick (fair)
    Cutlet – None


    1.52 Carats
    Polish – Excellent
    Symmetry – Very Good
    Flour – None
    Price – $12.7K
    Depth – 68.8 (very good)
    Table – 63 (excellent)
    Length to width – 1.25 (very good for a rectangle)
    Girdle – Thick to Very Thick (good)
    Cutlet – None

  10. Avatar
    Paul Gian-
    September 8, 2017 at 6:15 am

    Doug, the price differences could be a result of various factors. With yellow colored diamonds, you cannot buy or make decisions without videos/photograhs. This is because factors like color distribution, eyecleanliness, shape appeal and etc… cannot be deciphered.

    This would shed more light: https://beyond4cs.com/fancy-colored/cushion-cut-fancy-intense-yellow-diamond-engagement-ring/

  11. Avatar
    November 17, 2017 at 12:10 am

    Hi there Paul, I’m looking at cushion cut diamonds under 1 carat and am tossing up between two on Blue Nile:
    LD09315409 $3254
    LD09355704 $2655

    The cheaper stone has a thicker girdle and only a Good rating for symmetry, which I’m unsure about.
    I’m not worried about a G colour as I will be setting in yellow gold and I heard that meant a whiter colour isn’t as important as if you were setting in white gold/platinum?

    Hope you can give some advice!


  12. Avatar
    Paul Gian-
    November 19, 2017 at 4:24 am

    Between the 2, this is the better cut diamond for light performance:


    You are right about the color issue with yellow gold setting. An F or G would still look yellowish in that setting. Anyway, color is not my primary concern here. Cut quality is. Go for the diamond above.

  13. Avatar
    Len Murtha-
    December 8, 2017 at 2:53 pm

    Paul: Can you advise me on whether to choose 14k or 18k yellow gold? Also, given I am going with yellow gold, can you guide me on how to choose. My primary concern is brilliance and the “look” to the naked eye. Size: 1.5 carat. Round. Set high with channel diamonds on each side. Also, does it matter that I match diamond color with channel diamonds color? Thanks!! I will buy on bluenile.

  14. Avatar
    Paul Gian-
    December 9, 2017 at 3:30 am
  15. Avatar
    December 28, 2017 at 1:15 pm

    Question: do all solitaire diamonds have a girdle reflection. If not, what do I need to consider to avoid this? What is the ideal girdle thickness for an oval? Would it matter if it is a 0.5ct or a 3ct diamond? Or what it be the same recommended thickness regardless? I’m looking for a three carat oval ring.

  16. Avatar
    Paul Gian-
    December 29, 2017 at 1:51 am

    All diamonds will have a girdle reflection when seen from the profile view. The ideal girdle thickness for oval shapes and other fancy cuts should be between thin to very thick. It doesn’t matter what carat size you are buying as girdle thickness is measured as a relative to the diamond’s depth. Lastly, this article on shopping for a 3 carat oval diamond ring should help as well.

  17. Avatar
    March 4, 2018 at 6:18 pm

    Hi Paul. Thank you for the info. What do you think of this JA oval?


    It seems that there was an updated GIA report here where the SYMM was updated from good to very good: https://www.gia.edu/report-check?reportno=1275956429

    I am waiting on an ASET image. I am not sure about the 6 facet pattern and the thin to medium girdle. What do you think? Seems there is no bowtie but wondering about fire and brilliance – and the girdle thickness. Thank you.

  18. Avatar
    Paul Gian-
    March 5, 2018 at 6:59 am

    The grading reports are pretty inconsistent but I would assume that the one listed at GIA’s official website is accurate compared to the one uploaded by James Allen. Anyway, the diamond is pretty well cut for light performance and is a good choice. The bowtie is minimal and the girdle thickness is perfectly fine. Let me know again when you receive the ASET imagery from them.

  19. Avatar
    September 10, 2019 at 6:24 pm

    I have a 40 year old diamond, now that I am older 65 and more aware of diamond 4 c’s-Thanks interent, I see an area of slight chips in one area on the girdle and on up to one facet on the crown and another area of a line on the girdle maybe a feather – looks like fissure so to speak very minuscule, question can the bearded area be polished out, the girdle here is thin or just put a bezel ring setting on it and forget about it. It was listed as SI1,H ,1.5 carats years ago. Was the bearding caused by wear and tear, I really never wore it that much or was it a bad cutting process to begin with? Maybe I should just throw it in the garbage, lol.

  20. Avatar
    Paul Gian-
    September 11, 2019 at 9:01 am

    If you the diamond has a bearded girdle, it is unlikely to be caused by wear and tear. Most of the time, damage caused to the diamond result in nicks or chips. Polishing out a bearded girdle is relatively simple and results in small carat weight loss only. If the damage is a nick or chip, it is hard to say without looking at the diamond on the type of repairs that can be done. Your best way forward is to bring the ring for assessment with a jeweler.

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