How to Read a GIA Diamond Grading Report

Report Number & Date

Every GIA report has a unique report number, which is laser-inscribed on the diamond’s girdle (the thin edge between the crown and pavilion). The date shows when the GIA graded the stone. Use the report number to verify the certificate at report.gia.edu — you should always verify the certificate independently.

Shape & Measurements

This section lists the diamond’s shape (e.g., Round Brilliant, Oval Modified Brilliant, Emerald) and its precise dimensions in millimetres. For round stones, it shows minimum diameter × maximum diameter × depth. For fancy shapes, it shows length × width × depth.

Carat Weight

The precise weight to the nearest 0.01ct (and for smaller stones, 0.001ct). Note that carat is weight, not size — a 1.0ct round brilliant is approximately 6.5mm in diameter, but this varies depending on cut proportions.

Colour Grade

GIA grades colour on a scale from D (colourless) to Z (light yellow/brown). D, E, F are colourless; G, H, I, J are near-colourless. The colour is graded face-down under controlled lighting against master comparison stones. For lab-grown diamonds, GIA uses the same scale and the same grading process.

Clarity Grade

The GIA clarity scale: Flawless (FL), Internally Flawless (IF), VVS1, VVS2 (very very slightly included), VS1, VS2 (very slightly included), SI1, SI2 (slightly included), I1, I2, I3 (included). VS1–VS2 are eye-clean for virtually all shapes. The report includes a “plot diagram” showing the location of any inclusions.

Cut Grade (Round Brilliants Only)

GIA grades cut for round brilliants on a scale of Excellent, Very Good, Good, Fair, Poor. This grade accounts for brightness, fire, scintillation, weight ratio, durability, and finish. GIA does not grade cut for fancy shapes (ovals, pears, cushions, etc.) — for these, consult the Polish and Symmetry grades.

Polish & Symmetry

Polish describes the smoothness of each facet surface; Symmetry describes the alignment and proportion of facets relative to each other. Both are graded Excellent, Very Good, Good, Fair, or Poor. Excellent/Excellent is ideal; Very Good/Very Good is excellent value.

Fluorescence

Fluorescence describes how the diamond glows under UV light. GIA grades it None, Faint, Medium, Strong, or Very Strong (usually blue). Most experts recommend None to Faint. Strong fluorescence can, in some cases, cause a “haziness” in D–F diamonds under bright sunlight — though in lower colour grades (I–J), it can actually improve the apparent whiteness.

The Plot Diagram

The plot is a diagram of the diamond showing the location and type of every inclusion (marked in red for internal characteristics) and blemish (marked in green for external characteristics). Common inclusions include crystals (small mineral particles), feathers (small fractures), needles (thin crystal formations), and clouds (clusters of tiny crystals).

How to Verify on the GIA Website

Go to report.gia.edu, enter the report number from your certificate, and the GIA will display the full record including the grades, the plot diagram, and a photograph of the diamond. All our GIA-certified diamonds can be verified this way.

IGI Report Differences

The IGI (International Gemological Institute) uses the same 4C grading system as the GIA but applies it slightly differently. Some gemologists note that IGI clarity grades can run one grade more generous than equivalent GIA grades. Verify IGI reports at igiworldwide.com/verify. Both certificates are fully accepted and respected worldwide.