I was completely confused by this when I started shopping. Here is what I figured out after a lot of research.
GIA (Gemological Institute of America)
- Founded 1931, the original and most trusted grading lab
- Grading is strict and consistent — a GIA G-VS1 is reliably a G-VS1
- Preferred for natural diamonds
- Adds approximately 10–15% to the diamond's price premium
- Diamond dealers and resellers universally accept GIA at face value
IGI (International Gemological Institute)
- Widely used, especially for lab-grown diamonds
- Grading is slightly more lenient than GIA on natural stones (a GIA H might be an IGI G)
- For lab-grown diamonds: IGI has become the industry standard and grading is reliable
- Significantly cheaper certification, so diamonds cost less
My practical recommendation:
- Natural diamond: always GIA. The premium is worth it for accuracy.
- Lab-grown diamond: IGI is fine and widely accepted. You're not losing anything meaningful.
What to avoid:
EGL (European Gemological Laboratory) — their grading is notoriously inconsistent. I would not buy an EGL-certified stone. Neither would most serious dealers.
I bought a GIA-certified natural 1ct and am very happy. But if I'd gone lab, I would have been completely comfortable with IGI.
Anyone else have experience comparing the two in person?
Avoid EGL — this cannot be overstated. I almost bought an EGL stone thinking it was a deal. It was graded 2 grades more favorably than GIA would have graded it.