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Ten Methods:Determine which organization provided the diamond grading certificate.Look for the cut.Check the date.Check the carat weight.Evaluate measurements for a round diamond.Evaluate measurements for fancy cut diamonds.Note the clarity rating.Review the color.Examine the proportions section.Note the finish.

Before you purchase a diamond, make sure you know how to read its grading certificate so you don't waste money on a flawed stone.


Method 1 of 10: Determine which organization provided the diamond grading certificate.

  1. 1
    Hoge Raad voor Diamant (HRD), or "Diamond High Council," is Europe's counterpart to the GIA.
    • HRD's grading certificates are legal documents in the eyes of the European Union.
  2. 2
    The Precision Gem Grading Laboratory (PGGL) in Philadelphia, PA, uses ImaGem's Direct Measurement technology for objective diamond grading.
    • ImaGem's technology grades diamonds based on measurement of color, clarity, fluorescence and light behavior. They have the capability to support all grades with numerical measurements.
  3. 3
    The International Gemological Institute (IGI) mostly conducts appraisals for diamond engagement rings.
  4. 4
    The American Gem Society (AGS) certifies diamonds based on their cut grade from 0 (most desirable) to 4 (least desirable).
  5. 5
    The Gemological Institute of America (GIA) is a non-profit institute that created the "four Cs" (Cut, Clarity, Color and Carat Weight) methodology of grading diamonds, as well as the International Diamond Grading System.
    • Reports from this institute omit certain aspects of diamond cuts that other reports cover (e.g. crown height percentage, pavilion depth percentage, crown angle, pavilion angle).
    • Keep in mind that the GIA issues a report not a certificate.
  6. 6
    The European Gemological Laboratory (EGL) is an independent network of diamond grading laboratories.
    • Grading standards vary from one EGL laboratory to another. Therefore, diamond certificates from the EGL are generally less reliable than those from the GIA[1].

Method 2 of 10: Look for the cut.

  1. 1
    This is the most vital information to determine, as it summarizes the beauty of the stone.
  2. 2
    To know how well a diamond has been cut, make sure the certificate grades the gem's cut or light behavior based on direct measurement.
    • Beware of labs that list cut grades based on a model and not the actual diamond.
  3. 3
    Make sure the grading certificate includes light behavior grades and numerical measures for brilliance, sparkle and intensity.
    • If it does not, you have the right to ask your jeweler for an independent light behavior grading certificate.

Method 3 of 10: Check the date.

  1. 1
    A diamond grading certificate only details the gem's properties at the time of inspection, so it means virtually nothing if the diamond was altered afterwards.
  2. 2
    The older the certificate, the greater the chance that the diamond has been altered (e.g. set or worn).
  3. 3
    If the certificate is over a year old or has no date, make arrangements for re-certification.
    • If this is not possible, at least ask about the diamond's history and inspect the stone under a scope for abrasion around its girdle (the narrow band around the outer circumference of a diamond, where it is held by the jewelry setting).[2]

Method 4 of 10: Check the carat weight.

  1. 1
    One carat is equal to 1/142 of an ounce.
    • Generally, the higher the carat weight, the higher the price; however, prices leap at certain weights, and some weights are more popular (and thus more expensive) than others.[3]
  2. 2
    Your diamond's carat weight will likely be slightly above the one indicated on the certificate.
    • It is important to note that the carat weight is not the visual size of the diamond. It is possible for a .97 carat diamond to be wider than a 1.03 carat diamond.

Method 5 of 10: Evaluate measurements for a round diamond.

  1. 1
    Grading certificates list a maximum and minimum diameter for round diamonds, since no diamond is perfect. The difference between these two diameters is scrutinized in relation to carat.
    • For example, a round diamond with a measurement of 6.50 x 6.56 x 4.72 mm may have a diameter that varies by 0.06 mm. This number is the difference between the first two measurements listed.
  2. 2
    Standard diameter variances for round diamonds:[4]
    • 0.5 carat - 0.05 mm
    • 0.6 carat - 0.06 mm
    • 0.7 carat - 0.07 mm
    • 0.8 carat - 0.08 mm
    • 0.9 carat - 0.09 mm
    • 1.0 carat - 0.10 mm
    • 2.0 carat - 0.12 mm
    • 3.0 carat - 0.14 mm
    • 4.0 carat - 0.16 mm
    • 5.0 carat - 0.17 mm

Method 6 of 10: Evaluate measurements for fancy cut diamonds.

  1. 1
    For fancy shapes, divide the diamond's length by its width to determine the ratio.
    • If your answer is 1.8, for example, then the ratio is 1.8:1.
  2. 2
    Standard ratios for fancy shapes:[5]
    • Pear - 1.50:1 to 1.75:1
    • Marquise - 1.80:1 to 2.20:1
    • Emerald - 1.30:1 to 1.50:1
    • Princess - 1.15:1 to 1.00:1
    • Radiant - 1.50:1 to 1.75:1
    • Heart - 1.25:1 to 1.50:1
    • Oval - 1.30:1 to 1.50:1

Method 7 of 10: Note the clarity rating.

  1. 1
    Clarity grading systems vary. Consult the organization that produced the certificate for information on what each clarity measurement means.
  2. 2
    The clarity ratings for the GIA are listed here as an example:
    • FL = Flawless. No internal inclusions or external irregularities visible under 10x magnification to a trained eye.
    • IF = Internally Flawless. No internal inclusions but possibly tiny external irregularities in the finish visible to trained eye under 10x magnification.
    • VVS-1 = Very Very Slightly Included 1. Usually one very tiny inclusion visible only to a trained eye under 10x magnification.
    • VVS-2 = Very Very Slightly Included 2. Tiny inclusions visible only to a trained eye under 10x magnification.
    • VS-1 = Very Slightly Included 1. Some very small inclusions visible to anyone with 10x magnification.
    • VS-2 = Very Slightly Included 2. Several very small inclusions visible to anyone with 10x magnification.
    • SI-1 = Slightly Included 1. Small inclusions visible to anyone with 10x magnification.
    • SI-2 = Slightly Included 2. Several small inclusions visible to anyone with 10x magnification.
    • SI-3 = Slightly Included 3. Inclusions are visible to the naked eye of a trained observer.
    • I-1 = Included 1. Flaws that are visible to the naked, untrained eye.
    • I-2 = Included 2. Many flaws clearly visible to the naked, untrained eye that decrease the diamond's brilliance.
    • I-3 = Included 3. Many flaws clearly visible to the naked, untrained eye that decrease brilliance and compromise structure, making the diamond vulnerable to cracking or chipping.

Method 8 of 10: Review the color.

  1. 1
    Each lab has its own color grading system to differentiate diamond hues. As a rule, however, colorless diamonds are more expensive and desirable than yellow or brown diamonds.
  2. 2
    Blue, green, pink, red and some yellow diamonds may also increase or decrease in value depending on market demand.
  3. 3
    Avoid diamonds with brown or grey overtones, since they will negatively affect market value.[6]

Method 9 of 10: Examine the proportions section.

  1. 1
    Depth refers to the total depth of a diamond from table to culet, as a percentage of its total diameter. The desired depth percentage depends on the shape of the diamond[7]
  2. 2
    Culet refers to the bottom of a diamond that ends in a point. It may be faceted to protect the fragile tip from chipping.
  3. 3
    Table refers to the average width of a diamond. Smaller table percentages have become more popular in the US over the last five years[8]
  4. 4
    Girdle refers to the thickness of the diamond's girdle and and whether it is faceted.

Method 10 of 10: Note the finish.

  1. 1
    Before buying a diamond, be sure its certificate lists each of the following finish qualities as "good" or better:
    • Polish
    • Symmetry
    • Fluorescence
      • Opinions vary on the desirability of fluorescence in a diamond. Strong fluorescence in slightly yellow diamonds may make them appear whiter. But strong fluorescence in white or fancy colored diamonds is generally less desirable.
  2. 2
    On some diamond grading reports, the finish section details other characteristics of the stone not covered by the general report, like minor inclusions or inscriptions [9]


  • Practice reading several diamond grading certificates before you visit a store to make a purchase.
  • A diamond grading certificate or report should not assign monetary value to the stone, and is only provided for loose diamonds.


  • If your diamond grading certificate contains any statement about monetary value, it is only an appraisal. Appraisals can be done by anyone, including the salesperson selling the diamond, and are necessarily subjective (unlike grading certificates).
  • An appraisal by a GIA gemologist is not the same as a grading certificate or report. A GIA Graduate Gemologist (G.G.) is simply someone who has passed GIA courses in diamond evaluation. Only GIA GTL (Gem Trade Lab) Graders have the proper education and training to issue a grading certificate.[10]

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