What is a diamond certificate?
A diamond certificate (also called a grading report) is an independent assessment of a diamond's characteristics by a gemological laboratory. The lab evaluates the 4Cs along with measurements, proportions, fluorescence, and additional details — and issues a written report.
A certificate is your guarantee. It is the only objective record of what the diamond actually is. Never buy a fine diamond without one.
The major laboratories
GIA (Gemological Institute of America) — Founded in 1931, GIA is the gold standard for natural diamond grading. Universally accepted, consistent, and conservative in its grading. Most natural diamonds above 0.5ct should have a GIA certificate.
IGI (International Gemological Institute) — Founded in 1975, IGI is the leading authority for lab-grown diamonds. IGI's lab-grown grading is highly trusted; their natural grading tends to be slightly more lenient than GIA.
AGS (American Gem Society) — Founded in 1934, AGS is known for its proprietary 0–10 cut grading scale, considered by some to be even more rigorous than GIA's. As of 2023, AGS reports are issued through GIA.
GCAL (Gem Certification & Assurance Lab) — A New York laboratory widely used for lab-grown diamonds. GCAL is known for its 8X cut grade, a standard above Ideal that also assesses the diamond's optical symmetry.
HRD Antwerp — Belgium's diamond grading laboratory, widely used across the European market.
Certificates we accept
We exclusively list diamonds graded by GIA, IGI, GCAL, AGS or HRD. Every listing shows its grading laboratory, and you can filter by lab under Certification. We don't list uncertified diamonds, or reports from laboratories such as EGL whose grading standards have historically been inconsistent.
GCAL 8X proportions
GCAL publishes the proportion ranges an 8X diamond must fall within for each shape — round, oval, pear, princess, marquise, radiant and cushion. When a GCAL-certified diamond's report shows table, depth, crown and pavilion angles, length-to-width ratio and culet inside those ranges, with Excellent polish and symmetry, we mark it Meets GCAL 8X proportions.
This is not an 8X grade. GCAL awards 8X only after its own optical assessment of brilliance, fire, scintillation, optical symmetry and shape — measurements that aren't on a standard report. A diamond with 8X proportions is a strong candidate for 8X certification, and we can arrange it on request: use the GCAL 8X link on any diamond's page to ask us.
What's on a certificate
A typical GIA report includes:
- Unique report number (laser-inscribed on the diamond's girdle for verification)
- Shape and cutting style
- Carat weight
- Cut grade (round only)
- Colour grade
- Clarity grade
- Polish and symmetry grades
- Fluorescence
- Measurements (length, width, depth in mm)
- Proportions (table %, depth %, crown angle, pavilion angle, girdle thickness, culet)
- Plotted diagram showing inclusion positions
Verifying a certificate
Every GIA, IGI, GCAL, AGS, and HRD certificate has a unique number that you can verify on the issuing laboratory's website. If a seller cannot provide the certificate or the number doesn't match the lab's records — walk away.