Reviewed by Raiha Buchanan, Graduate Gemologist at Carateu
To read a diamond certificate, first verify its report number on the issuing laboratory's website. Then confirm whether the diamond is natural or laboratory-grown and review its measurements, carat weight, colour, clarity, cut or finish, fluorescence, comments and inscriptions. A grading report describes the stone; it does not set its price or guarantee how attractive it will look in person.
People often call this document a certificate, but GIA and IGI issue diamond grading reports. The steps below explain what each part means and what to check before comparing diamonds.
How to read a diamond certificate in eight steps
1. Verify the report number
Every GIA or IGI report has a unique number. Look it up using the laboratory's official service:
Compare the online record with the document, including the report date, diamond origin, shape, measurements and grading results. Where a laser inscription is present, ask the retailer or gemologist to confirm that the number on the diamond's girdle matches the report. A matching online record confirms that the report data is held by the laboratory; matching the inscription and measurements helps confirm that the report belongs to that physical stone.
2. Confirm natural or laboratory-grown origin
Read the description or identification line before looking at the grades. It should state whether the stone is a natural diamond or a laboratory-grown diamond. A laboratory-grown report may also identify the growth method, such as CVD or HPHT, and whether post-growth treatment was detected, depending on the laboratory and report type.
3. Read the shape, cutting style and measurements
The shape is the outline, such as round, oval, emerald, radiant or cushion. The cutting style describes the facet arrangement, such as brilliant, step or mixed cut.
Measurements are recorded in millimetres. Round diamonds are usually shown as minimum diameter × maximum diameter × depth. Fancy shapes are generally shown as length × width × depth. These figures help you judge face-up size and proportions because two diamonds with the same carat weight can look different in size.
4. Check the carat weight
Carat is a measure of weight, not visible size. One carat equals 0.2 grams. Compare carat weight with the measurements and depth rather than judging the weight alone.
5. Understand the colour grade
For diamonds graded on the D-to-Z scale, D is colourless and increasing letters indicate more visible yellow or brown body colour. The appearance of a grade can vary with the diamond's shape, size, setting and lighting.
6. Understand the clarity grade and plot
Clarity records internal characteristics called inclusions and surface characteristics called blemishes, assessed under magnification. The grade is useful, but the type, size, position and visibility of the characteristics also matter.
If the report includes a clarity plot, use it as a map. Look for where characteristics sit, whether they are central or near the edge, and whether the comments section lists features that are not shown on the diagram. A clarity grade alone does not guarantee that a diamond will be eye-clean.
7. Read cut, polish, symmetry and proportions
Standard round brilliant diamonds often receive an overall cut grade. Fancy shapes may not have the same overall cut grade, so pay closer attention to measurements, proportions, polish, symmetry and a good-quality video or visual inspection.
- Cut grade assesses how well the proportions and craftsmanship support brightness, fire and scintillation for report types where a cut grade is provided.
- Polish describes the quality of the diamond's finished surface.
- Symmetry describes the alignment and balance of its facets and outline.
- Proportion diagram records measurements such as table, depth, crown and pavilion information where provided.
8. Check fluorescence, comments and inscriptions
Fluorescence describes the diamond's reaction to long-wave ultraviolet light. The comments section can disclose treatments, extra identifying characteristics or grading details not shown elsewhere. The inscription field records any text or report number noted on the girdle.
GIA vs IGI diamond reports
Both laboratories identify and grade diamonds, but report formats and services differ. Compare the fields on the individual report rather than relying on the laboratory name alone.
| What to compare | GIA | IGI |
|---|---|---|
| Natural diamonds | Report types can include the 4Cs, measurements, proportions, clarity characteristics, comments and security features, depending on the service. | Natural diamond report formats can include the 4Cs, measurements, proportions, clarity characteristics and comments. |
| Laboratory-grown diamonds | GIA currently uses a distinct quality assessment for colourless to near-colourless laboratory-grown diamonds, with Premium or Standard classifications. Older GIA reports may use a different format. | IGI offers dedicated laboratory-grown diamond reports that commonly record detailed grades, origin and additional growth or treatment information where applicable. |
| Online verification | Verify through GIA Report Check. | Verify through IGI's report lookup. |
Laboratory services and report formats can change. Always use the issuing laboratory's current verification page and interpret the fields shown on the specific report. For a deeper comparison, read IGI vs GIA diamond certification.
Diamond certificate authenticity checklist
- Use the official GIA or IGI lookup, not a copied report hosted only by a seller.
- Confirm the online data matches the document exactly.
- Match the report number to the girdle inscription where an inscription is present.
- Check that the shape and measurements agree with the diamond.
- Read the comments for treatments, origin notes and additional identifying information.
- Ask a qualified gemologist to inspect the stone if anything does not match.
Use the report to compare diamonds
A report is a structured description, not a beauty score or valuation. Compare the report with videos, face-up appearance and professional inspection. Start with our guide to the diamond 4Cs, then use Carateu's diamond certificate lookup to find a matching listing by GIA or IGI report number.
Ready to compare stones? Browse loose diamonds or explore loose laboratory-grown diamonds in Europe.
Frequently asked questions
Is a diamond certificate the same as a grading report?
In everyday language, yes. GIA and IGI generally use the term grading report because the document records identification and quality characteristics rather than guaranteeing value.
Does a diamond certificate prove that the stone is genuine?
The laboratory report records the result for the stone submitted for examination. Verify the report online and match its number, measurements and any girdle inscription to the physical diamond.
Does a GIA or IGI report show the diamond's price?
No. A grading report describes the diamond's characteristics. It is not an appraisal and does not assign a retail or resale value.
Can an older diamond report still be valid?
An older report can still describe the diamond accurately if the stone has not been damaged, re-cut or altered. Verify it online and consider a professional inspection when the report is old or the diamond's history is unclear.
