How to read a diamond grading report (GIA and IGI)

A diamond grading report is an independent lab's description of a single stone, written after the lab has weighed, measured and examined it. In practice it answers four questions: what is this diamond, how heavy is it, how did the lab grade the 4Cs, and which marks and features make this stone different from every other one.

GIA, the lab this guide uses as its model, issues its Diamond Grading Report only for loose natural diamonds of 0.15 carats or more. Smaller stones, such as the accent diamonds around a centre stone, do not get that report, which is why jewellery with many small diamonds is usually described by total carat weight instead.

The notice printed on GIA's sample report says the results refer only to the diamond described, were obtained with the techniques and equipment available at the time of examination, and are not a guarantee or valuation. Read a report as a precise description, not a verdict on whether the stone is a good purchase.

GIA's own guide to its report numbers twenty-one items across the three panels of the folded sample document. The first panel holds the identification and grades, the second the proportions diagram and clarity plot, and the third the grading scales, security features and a QR code. GIA's sample is a few years old, so a current report may differ in layout and wording. The table lists the fields in the order you will meet them, with the one check worth making on each.

Carat weight is a measure of mass. One carat is 0.2 grams, and a carat divides into 100 points, so a 0.75 carat stone is a 75-point stone. GIA often measures weight to the hundred-thousandth of a carat and rounds it to the nearest hundredth for the report. Weight alone does not say how large the diamond looks.

That is the job of the measurements. For a round diamond the report gives a minimum and maximum diameter and the depth, written like 6.41 to 6.43 × 3.97 mm. For a fancy shape the report gives length, width and depth, and dividing length by width gives the outline's ratio, a quick way to compare two pears of the same weight. The diamond shapes guide explains how outline changes the look.

You can also use the numbers to check the report's own diagram. In GIA's sample report, a round diamond of 1.01 carats measures 6.41 to 6.43 × 3.97 mm. Dividing the depth by the average diameter (3.97 ÷ 6.42) gives about 61.8 per cent, which is the depth percentage printed on the sample's proportions diagram. The carat weight entry covers the unit in more depth.

Colour on a GIA report is the absence of colour in a white diamond, graded from D (colourless) to Z (light yellow or brown). GIA graders compare the stone to master stones of known colour, and they do so with the diamond table-down in a grading tray, which makes small differences easier to judge than they would be in a ring. GIA groups the letters as colourless (D to F), near-colourless (G to J), faint (K to M), very light (N to R) and light (S to Z). Neighbouring letters are hard to tell apart by eye. Diamonds with more colour than Z are graded as fancy coloured diamonds, with a different vocabulary.

Clarity is the relative absence of inclusions (internal marks) and blemishes (surface marks), judged at 10× magnification. GIA looks at five things about each mark: size, nature, position, colour or relief, and quantity. The scale has eleven grades, summarised below. Ten-times magnification is the reference, not how anyone looks at a ring, so ask whether you can see the marks without a loupe. GIA describes "eye-clean" as an informal industry term, not an official GIA one. Learn more about the marks themselves in the entry on inclusions, and about the full system in the 4Cs guide.

A cut grade appears only on some reports. GIA's cut scale, from Excellent to Poor, applies to standard round brilliants in the D-to-Z colour range. Other shapes receive no cut grade, though polish and symmetry are still graded. As of mid-2026, a trade report says GIA intends to add cut grades for marquise, oval and pear shapes in 2027, so check the date on any report you are shown. If you are looking at a round brilliant, the cut grade is the grade that most affects how lively the stone looks.

GIA builds the cut grade from seven components. Three describe appearance: brightness, fire and scintillation. Four describe design and craftsmanship: weight ratio, durability, polish and symmetry. Each grade covers a range of proportion combinations, so two Excellent stones can look slightly different. For fancy shapes, the best checks are the polish and symmetry grades, the measurements, and the stone itself in good light.

Polish is the smoothness of the surface. Symmetry is the exactness of the outline and the shape, placement and alignment of the facets. Both are graded from Excellent to Poor. On a round stone, Excellent on cut, polish and symmetry is trade shorthand for "triple Excellent".

Fluorescence is the glow some diamonds give off under long-wave ultraviolet light. On a GIA report its strength is recorded as None, Faint, Medium, Strong or Very Strong, alongside the colour of the glow. None covers a range from indiscernible to very faint, and only about 25 to 35 per cent of diamonds show any fluorescence, with more than 95 per cent of those glowing blue.

Does it change how the diamond looks? GIA's research found that blue fluorescence has little to no effect on transparency except in extremely rare cases, and that average consumers did not see systematic differences between fluorescent and non-fluorescent stones. Some trade professionals believe a blue glow can make higher colour grades look hazy or oily, a view GIA says persists despite its findings. What GIA does report is price: stones in the higher colour grades with very strong fluorescence often sell for less than stones without it, even though their colour and transparency are most likely unaffected. That can be a saving if you view the stone yourself and are happy with it. See diamond fluorescence for more.

The clarity characteristics plot is a drawing of the stone, seen from the crown (top) and the pavilion (bottom), with symbols marking each inclusion or blemish. The symbols show the type or nature, position and approximate size of each mark. On GIA's sample, red symbols mark internal characteristics (inclusions) and green or black symbols mark external ones (blemishes). The plot is explicitly an approximation: GIA's own footnote says all clarity characteristics may not be shown and details of finish are not shown.

The plot matters because the grade alone hides position. The closer an inclusion sits to the centre of the table, the greater its effect on the clarity grade, and feathers near the girdle or running about a third of the way or more into the stone can make a diamond more vulnerable to chipping. Two SI1 diamonds can therefore differ: one with a small mark near the edge, one with a cluster under the table. Ask to be shown each plotted mark on the stone.

The proportions diagram is a profile drawing of the diamond's actual proportions, from table size and depth to crown and pavilion angles, girdle thickness and culet. It shows the proportions a round stone's cut grade rests on. Use it to compare similar stones, not to judge one against a rule of thumb, because each cut grade accepts many combinations. The entry on diamond proportions explains each term.

The comments field lists additional identifying characteristics that appear nowhere else on the report. If a treatment is detected, such as laser drilling, it would be described here. A colour treatment is also flagged by an asterisk next to the colour grade. Because a treatment can affect what a diamond is worth and how it should be cared for, read any entry in the comments carefully, and ask what it means in plain words. The entry on diamond treatments covers the usual ones.

The inscription field lists any text, symbol, logo or unique report number inscribed on the girdle, the thin edge around the stone's widest point. A laser inscription of the report number is how a loose stone and its paper are tied together. Ask to see the inscription under magnification and compare it with the report number character by character. Once a stone is set, metal may cover part of the girdle, so do this before the diamond goes into a ring.

The third panel shows the scales, and the security features GIA lists (microprinting, security screens, watermarks, a two-dimensional barcode, a hologram and sheet numbering) are there to protect the report's integrity and help authenticate the document.

There are three checks, and each one covers a different risk.

1. Look up the report number online. GIA registers each report number in its database, and its sample report says to verify the report at gia.edu. GIA's Report Check lets you confirm that your report matches what the lab has archived; it covers reports issued on or after January 1, 2000. Do the same with any other lab: use the lab's own website, typed in yourself, not a link supplied by a seller.
2. Scan the QR code. The QR code on its report, when scanned, verifies the report's data against its database.
3. Match the stone to the paper. Compare the inscription on the girdle with the report number, then the carat weight and measurements with the figures on the report. If your jeweller can weigh the stone, a weight that differs from the report deserves an explanation.

If anything disagrees, such as a different weight, a number that will not match, or a stone with no inscription when the report lists one, pause the purchase. Ask the seller to explain. Do not accept the explanation that the stone is the same one regardless. A report you cannot tie to the stone tells you nothing about it. The same care applies to a copy or a photograph of a report: a copy is only as reliable as the online record behind it.

A GIA Diamond Grading Report is issued for natural diamonds, and GIA's lab-grown paperwork has changed more than once, so the date matters. In reports introduced on October 13, 2020, GIA graded lab-grown diamonds on the same colour and clarity scales as natural ones, while pointing out that those grades do not match the way rarity works in nature. Those reports showed the 4Cs, plotted clarity and proportions diagrams, the growth method (CVD or HPHT) and whether post-growth colour treatment had been applied.

From October 1, 2025, GIA's Laboratory-Grown Diamond Quality Assessment replaced those grades for colourless to near-colourless stones of 0.15 carats or more with two descriptive categories, Premium and Standard. GIA's stated reason is that more than 95 per cent of lab-grown diamonds entering the market fall into a very narrow range of colour and clarity. A report issued before that date will show the older format. A stone with the newer paperwork will not show a D-to-Z colour letter or an FL-to-I3 clarity grade. If you are comparing a lab-grown diamond with a natural diamond, compare like with like, and read lab-grown vs natural diamonds for the wider decision.

GIA laser inscribes the lab-grown stones it assesses with the words Laboratory-Grown and a reference number, and that inscription is how the paperwork is tied to the stone. GIA's separate report for coloured lab-grown diamonds includes a plotted clarity diagram and an assessment of growth type and post-growth treatment.

The International Gemological Institute (IGI) is a separate laboratory that issues reports for both natural and lab-grown diamonds, along with other gemstones and jewellery. The method here carries over to any lab: match the report number to the stone, verify it on the lab's own website, then read the grades against the scale printed on that report. The layout, field names and scale wording may differ, so do not assume they match GIA's.

The American Gem Society is a good example of why. AGS grades cut, colour and clarity on a 0-to-10 scale in which 0 is the best grade, so a colour grade of 3 has less colour than a colour grade of 5, and a perfect stone is written as 0/0/0. Reading an AGS 0 as a low score would be an easy mistake. When you compare diamonds with reports from different labs, read each against its own scale and judge the stones by eye as well. Ask the jeweller which lab's report each stone has and why.

A report is a measurement tool, and it leaves several questions open.

• Price or value. GIA's notice states that the report is not a guarantee or valuation. A value for insurance is a separate document, a jewellery appraisal, written for a different purpose.
• How the stone looks in daylight. The grades describe ranges. Two stones with identical grades can differ in brightness, in where the inclusions sit, and in how the colour reads once it is set in metal.
• The ring. The report covers the loose diamond only. Setting, metal and the surrounding stones all change the look of the finished piece.
• The cut of fancy shapes. Without a cut grade, you need your own eyes and the measurements.

Treat the report as the starting point, then look at the stone itself. It also lets you compare diamonds fairly, for example by choosing a lower grade you cannot see and putting the savings toward weight or a better cut. The engagement ring budget guide shows how to weigh those trade-offs.

Use this order when a report is in front of you.

1. Confirm the lab, the report number and the date, then look the number up on the lab's own website.
2. Match the girdle inscription, carat weight and measurements to the stone.
3. Read the shape and cutting style, then decide whether the cut grade applies to this shape.
4. Read colour, clarity and, where present, cut, polish and symmetry, always against the scale printed on that lab's report.
5. Look at the clarity plot and ask where each mark is on the stone.
6. Read the comments and any asterisk, and ask for a plain explanation of any treatment.
7. Look at the stone in more than one kind of light before you decide.

If you are designing a ring around a diamond, the showrooms are where you can look at stones in person. The custom engagement rings and custom jewellery design pages explain how a design appointment works, and the design studio is a place to start a design. For the overall decision, how to choose an engagement ring puts the report in context, and the engagement rings collection shows finished examples.