GIA vs IGI: which diamond certificate should you trust?

If you're buying a diamond at any meaningful size in 2026, it should come with an independent certificate. The two names that dominate the certificate is from are GIA (Gemological Institute of America) and IGI (International Gemological Institute). They are not the same. Here's what actually matters.

The short version

• Natural diamond? Insist on GIA. It's the global benchmark and protects resale value.
• Lab-grown diamond? IGI is the industry standard. GIA is also fine.
• Anything else (EGL, HRD, in-house "certificates")? Treat with caution. Especially EGL.

What a diamond certificate actually does

Every diamond above 0.3ct should come with an independent grading report. The certificate is not the diamond's "value" — it's a technical specification: cut, colour, clarity, carat, polish, symmetry, fluorescence, measurements, and any treatments. The price you pay should be based on what's on the certificate, not what the seller says verbally.

No certificate = no objective reference point. Don't buy unsmall natural diamonds without one.

GIA — the global benchmark

The Gemological Institute of America is the world's most respected diamond grading lab. Founded 1931, headquartered in California, with labs in New York, Antwerp, Mumbai, Hong Kong and elsewhere. GIA grading is the strictest in the industry and the most globally trusted.

Why GIA matters for resale: when you (or your children) sell a diamond decades from now, a GIA certificate is universally accepted. Lesser labs may not be.

IGI — the lab-grown specialist

The International Gemological Institute is the world's largest grading lab by volume and the dominant lab for lab-grown diamonds — it grades the majority of CVD and HPHT diamonds produced worldwide. IGI is respected and used by major retailers globally.

For lab-grown, IGI is the standard and entirely sufficient. For naturals, IGI grading runs slightly more generously than GIA — the same physical stone may grade F at IGI and G at GIA. Knowing this matters when comparing prices.

How to read either certificate

The 4Cs

• Cut — Excellent / Very Good / Good. Pay for Excellent on round brilliants. It drives sparkle more than any other factor.
• Colour — D (colourless) through Z (yellow). D–F are colourless; G–J are near-colourless and look identical to the eye in most settings. Below J starts to show colour.
• Clarity — FL, IF, VVS1, VVS2, VS1, VS2, SI1, SI2, I1, I2, I3. VS1 and VS2 are eye-clean at any size — paying for VVS is generally wasted money unless collecting.
• Carat — weight, not size. A well-cut 0.9ct can look bigger than a poorly-cut 1.1ct.

Other things to check

• Polish & symmetry — Excellent / Very Good is what you want.
• Fluorescence — None or Faint is preferred. Strong/Very Strong blue can give the stone a milky appearance in daylight.
• Measurements — width, depth, table %. These reveal the cut quality.
• Laser inscription — the certificate number is etched on the diamond's girdle. Verifiable under magnification.

Labs to be wary of

• EGL (European Gemological Lab) — historically inflates grades by 1–3 grades. A stone marketed as "EGL F/VS1" may be GIA J/SI1. Avoid.
• In-house "certificates" — meaningless. The seller grading their own diamond is not independent.
• HRD (Belgium) — legitimate and respected in Europe but less universally accepted than GIA.
• AGS (American Gemological Society) — absorbed into GIA in 2022. Legacy AGS certificates remain valid.

What we recommend at 57 Jewellers

• Every natural diamond we set above 0.5ct comes with full GIA certification.
• Every lab-grown diamond we set comes with full IGI certification.
• We send the certificate PDF before purchase. You verify everything on the lab's website (gia.edu / igi.org) before paying.

If you've been shown a stone with an unfamiliar certificate (or no certificate at all), send the details on WhatsApp. We'll tell you what it's actually worth — and what to look for instead.