Diamond Education

Diamond Certificates

A grading report is what turns a seller's description into a verifiable fact. Which laboratory issued it matters as much as what it says.

By 25karats · Updated 2026 · 7 minute read

A diamond grading report, commonly called a certificate, is an independent laboratory’s assessment of a specific stone: its 4Cs, its exact measurements, its proportions, and a map of its inclusions.

It is not an appraisal and it does not state a value. What it does is let you compare two diamonds on the same terms, and hold a seller to a specific claim. Never buy a center stone without one.

The two laboratories that matter

Grading is a judgment call, and different laboratories make it with different degrees of rigor. Two are worth trusting for a diamond you are buying.

GIA

Gemological Institute of America

Non-profit, and the body that created the 4Cs system
The strictest and most consistent grading in the industry
The benchmark for natural diamonds
Since October 2025, no longer issues full 4Cs grades for lab-grown stones

IGI

International Gemological Institute

Independent, and long established internationally
Grades natural and lab-grown diamonds on the full 4Cs scale
The de facto standard for lab-grown diamonds
Every lab-grown diamond we sell carries an IGI report

For lab-grown diamonds, look for IGI. As of October 1, 2025, GIA describes lab-grown diamonds only as “Premium” or “Standard” rather than issuing color and clarity grades, on the reasoning that most lab-grown stones cluster in a narrow high-quality band. That is a defensible position, but it makes GIA reports useless for comparing one lab-grown stone against another. IGI still grades the full scale, which is why it has become the standard.

Reports to treat with caution. Grading standards vary widely, and some laboratories are known in the trade for running considerably more generous than GIA or IGI, sometimes by two or more grades on color and clarity. A stone that looks like a bargain on paper is often just leniently graded. Be equally wary of an “in-house” or “store” certificate: a report written by the seller about their own merchandise is not independent, whatever it is called.

What a report contains

The 4Cs

Cut grade (round diamonds only)
Color grade, D to Z
Clarity grade, FL to I3
Carat weight to two decimals

Measurements

Diameter or length × width
Depth percentage
Table percentage
Girdle thickness and culet size

Finish and extras

Polish grade
Symmetry grade
Fluorescence
Any treatments, disclosed

Identification

Report number
Issue date and laboratory
Laser inscription on the girdle
A plot showing inclusion positions

How to actually read one

Most people look at the four grades and stop. These are the parts that repay a second look.

The plot, where the inclusions sit

A diagram marking every inclusion the grader found. Inclusions under the table are in your line of sight; the same ones near the girdle will be hidden by a prong. Two stones with identical clarity grades can look very different, and the plot is how you tell in advance. See our guide to inclusions.

The measurements, how big it really is

Carat is weight; the millimeter measurements tell you the size you will see. A one-carat round should be around 6.5 mm. Noticeably less means weight is hidden in the depth, where it does nothing for you.

Polish and symmetry

Separate from the cut grade, and easy to miss. Aim for Very Good or Excellent on both. They matter especially for fancy shapes, which receive no overall cut grade.

Fluorescence

Usually lowers the price. On a near-colorless stone that can be a genuine bargain; on a D–F stone strong fluorescence occasionally causes haze. Covered in our color guide.

Comments and treatments

Read this section. Laser drilling, fracture filling, and clarity or color enhancement all appear here, and all substantially reduce what a stone is worth relative to an untreated equivalent.

Verify the report matches the stone

A report describes one specific diamond. Two checks confirm you are holding that diamond:

Check the laser inscription. Most graded diamonds carry their report number inscribed on the girdle, readable under magnification. Ask to see it.
Look the report up online. Both GIA and IGI let you verify a report number against their own database, which confirms the document is genuine and has not been altered.

One question is worth asking every time: “Which laboratory graded this, and can I see the report before I commit?” A seller who is vague about the answer, or who offers only their own paperwork, is telling you something useful.

Reports for lab-grown diamonds

Lab-grown diamonds are graded by the same laboratories, on the same scales, with two differences worth knowing.

Origin is always stated. The report identifies the stone as laboratory-grown, and the girdle inscription records it too. This is how origin is established, not by appearance, which is identical.
IGI is the practical choice. Since GIA stopped issuing full grades for lab-grown in October 2025, IGI reports are what allow you to compare stones like for like.

Every lab-grown diamond we sell is IGI certified. See our lab-grown diamond guide, or browse the certified inventory.

See it on real stones

Browse IGI-certified lab-grown diamonds by shape, carat, color, clarity and cut, at roughly 40–60% less than comparable natural stones.

Shop lab-grown diamonds Shop engagement rings

More on diamonds: The 4Cs, Cut, Color, Clarity, Carat weight, Shapes, Inclusions, and Conflict-free.