The Gemological Institute of America (GIA) is widely regarded as the gold standard in diamond grading. Founded in 1931 by Robert M. Shipley, GIA is the organization that created the 4Cs grading system (Cut, Color, Clarity, and Carat Weight) that the entire diamond industry uses today. When you see a diamond described as "G color, VS2 clarity," you are using GIA's language and scale.
Why GIA Is the Most Trusted Lab
GIA operates as a nonprofit organization dedicated to research and education, not profit. This independence is central to its credibility. GIA has no financial interest in the outcome of any grading report, which gives buyers and sellers confidence that the assessment is unbiased.
GIA's grading process is designed to eliminate subjectivity. Each diamond is graded by multiple independent gemologists who do not know each other's assessments. The final grade represents a consensus. This blind grading process is one reason GIA reports are so consistent — a diamond graded by GIA in New York will receive the same grade at GIA in Mumbai.
GIA Grading Scales
Cut: Excellent, Very Good, Good, Fair, Poor. GIA's Excellent cut grade considers proportions, symmetry, and polish together to evaluate how effectively a diamond returns light. Only round brilliant diamonds receive a cut grade from GIA; fancy shapes do not.
Color: D (colorless) through Z (light yellow or brown). GIA created this D-Z scale to provide a universal standard. Grades are determined by comparing the diamond face-down against master stones under controlled lighting. For more detail, see our diamond color guide.
Clarity: Flawless (FL), Internally Flawless (IF), VVS1, VVS2, VS1, VS2, SI1, SI2, I1, I2, I3. GIA gemologists examine the diamond under 10x magnification to identify inclusions and blemishes. The clarity guide explains each grade in detail.
Carat Weight: Measured to the hundredth of a carat using an electronic micro-balance.
GIA Report Types
GIA Diamond Grading Report: The full report, typically issued for diamonds 0.15 carats and larger. Includes a plotted clarity diagram showing the location and type of inclusions, as well as a proportions diagram. This is the most comprehensive report available.
GIA Diamond Dossier: A more compact report for diamonds typically between 0.15 and 1.99 carats. Includes all the same grades but without the plotted clarity diagram. The report number is laser-inscribed on the diamond's girdle for identification.
GIA Laboratory-Grown Diamond Report: Since 2020, GIA has issued full grading reports for lab-grown diamonds using the same grading scales. These reports clearly identify the diamond as laboratory-grown and note the growth method (HPHT or CVD) when determinable.
Verifying a GIA Report
Every GIA report can be verified online at GIA's Report Check service (gia.edu). Simply enter the report number and you can view the full grading details, confirm the report is authentic, and check that the diamond matches the listed specifications. If a seller provides a GIA report number, always verify it before purchasing.
GIA Laser Inscription
GIA can laser-inscribe its report number on the girdle (outer edge) of a diamond. This microscopic inscription is invisible to the naked eye but can be seen under magnification. It provides a permanent link between the physical diamond and its grading report, preventing any possibility of switching.