What your GIA report doesn’t tell you
A GIA report is the most trusted document in the diamond trade, and by policy it never mentions money. Enter the grades exactly as they appear on yours: you get a retail range, the honest resale figure, and the specific grades that are quietly costing you — or quietly working in your favor.
Copy the grades from your report
What a GIA report will not do
It will not give you a value. That is a deliberate policy, not an oversight — GIA grades stones and stays out of the business of pricing them, which is exactly why the trade trusts the grades. The consequence is that the most authoritative document about your diamond is silent on the only question most owners actually have.
It also will not tell you which of your grades were worth paying for. A report lists eleven or twelve facts with equal visual weight. In price terms they are nothing like equal, and two of them commonly move money in directions people do not expect.
| Line on your report | Effect on value | What it actually means |
|---|---|---|
| Carat weight | Very large | Price per carat steps up at 0.50, 0.70, 0.90, 1.00, 1.50 and 2.00 ct. A 0.96 ct and a 1.00 ct differ by a tenth of a millimeter face-up and thousands of dollars. |
| Color grade | Large | D to K spans roughly a 2.5× price range on an otherwise identical stone. Most of the difference is invisible once the diamond is set in a warm metal. |
| Clarity grade | Large | FL to I1 spans more than 3×. Everything from VS2 upwards is eye-clean, so above VS1 you are paying for a grade only a loupe can see. |
| Cut grade | Large — if it is there | Only round brilliants get one. It is the grade that most affects how the diamond actually looks, and fancy shapes do not have it. |
| Fluorescence | Medium, and it flips sign | The only grade whose effect on price reverses depending on your color grade. Explained in full below. |
| Polish and symmetry | Small above Good | Finish grades, not cut quality. Below Good they start to show and the stone gets harder to resell. |
| Measurements and proportions | Medium | Table and depth percentages reveal a badly proportioned stone that still carries good grades — and on fancy shapes they are most of what you have to go on. |
| Laser inscription | None directly | Lets you match the physical stone to the report. Worth confirming before you buy second-hand. |
Fluorescence: the one grade that changes the price without changing the diamond
Roughly a third of diamonds fluoresce, almost always blue, under ultraviolet light. It is the single most misunderstood line on a GIA report, because its effect on price reverses depending on your color grade.
In a colorless D, E or F, the trade treats blue fluorescence as a defect and discounts it — commonly 5% to 40%, with about 12% typical for Strong. But blue is the complement of yellow. In an I, J or K, the same fluorescence masks the faint tint and the stone can face up close to a grade whiter, so those stones trade flat to a slight premium.
| Your color grade | Effect on price | Faint | Medium | Strong | Very Strong |
|---|---|---|---|---|---|
| D E F Colorless | Discount | −1% | −5% | −12% | −18% |
| G H Near-colorless | Roughly neutral | 0% | −1% | −3% | −6% |
| I J K Faint tint | Flat to a small premium | 0% | +1% | +2% | +1% |
Effects above are typical retail adjustments on an otherwise identical stone, and the calculator applies them. Individual stones vary: a small minority of very strongly fluorescent diamonds look hazy or oily in daylight, which is discounted much harder than the table suggests. That is visible to the eye, so look at the stone.
A D color with strong blue fluorescence can price like a non-fluorescent stone several grades lower. We put numbers against every color grade in a separate piece: where fluorescence stops being a fault. If you are buying, that is the cheapest way to own a top color grade. If you are selling, it is the most common reason an offer comes in under what you expected.
Why your fancy shape has no cut grade
GIA grades cut for round brilliants and nothing else. An oval, pear, cushion, emerald or princess report carries Polish and Symmetry but no overall cut grade, because facet patterns and light behavior vary too widely between fancy shapes for one standard to cover them.
This causes a specific and expensive misreading. Shoppers see Excellent Polish, Excellent Symmetry and read it as a verdict on cut quality. It is not. Those are finish grades — how cleanly the facets were polished and how well they line up. Cut quality is about how the stone handles light, and on a fancy shape GIA has not graded it at all. Two ovals with identical reports can look completely different in the hand.
So on a fancy shape, judge with your eyes and the proportions, not the grades. GIA has said it will begin grading cut on marquise, oval and pear shapes in 2027, which will close part of this gap.
GIA, IGI and the rest — why the lab on the report matters to the price
Grading is a judgement, and different labs judge differently. GIA is the strictest of the major labs and the trade prices accordingly: the same physical stone graded by a softer lab will often carry a better-looking report and a lower price. That is not a conspiracy, it is just calibration, and it is why a report is only as meaningful as the name on it.
In practice a stone graded by a lab known to run softer needs to be discounted against the GIA equivalent before you compare prices — our valuation applies roughly 7% for that, and more for an ungraded stone. The gap is widest on lab-grown diamonds, where a large share of stones are graded outside GIA and color and clarity grades commonly read one to two grades better than a GIA equivalent would.
The practical rule: compare like with like. A G VS1 from one lab is not automatically a G VS1 from another, and if you are paying a premium for a grade, the lab that assigned it is part of what you are paying for. If you are buying second-hand, check the laser inscription against the report before anything else.
Verifying a report, and what to do if you have lost yours
Verify it at the source. GIA runs Report Check free for anyone — you do not need to be the client who submitted the stone. Enter the report number and you get the grades as GIA issued them. Always do this before buying a second-hand stone: it confirms the report is real and that the numbers on the paper in front of you have not been altered.
Match the stone to the paper. Most GIA-graded diamonds carry the report number laser-inscribed on the girdle. A jeweler can read it under magnification in seconds. A report that verifies correctly proves the report is genuine; the inscription is what ties it to the stone in your hand.
If you have lost the report, the stone has not lost its grades. If it is inscribed, the number is on the diamond and Report Check will return the full grading — a lost certificate is a paperwork problem, not a value problem. If there is no inscription and no number, the stone has to be re-submitted to be graded again. Either way, you can get a working value from the tool above using what a jeweler can tell you in a few minutes with a loupe and a scale.
Open GIA Report Check →Report Check is GIA's own free service and opens on gia.edu. CaratBase is independent of GIA and is not affiliated with, endorsed by or authorized by it. The grades are theirs; the valuation is ours.