Reflections Craft
Sign In

· 9 min read

How to Read a Diamond Grading Report, Line by Line

A jeweller's walkthrough of how to read a diamond grading report: what each field means, which grades change the price, and which ones you can ignore.

A grading report is a description of one specific stone, not a quality ranking and not an appraisal. Read it in four passes: confirm the report number and lab, check the measurements and weight, then the four grades, then the diagram and comments at the bottom where the awkward details live. Most of the price you pay is set by four lines on the page, and at least two of the other lines will not change what you see across a dinner table.

Start with the report number, not the grades

Every report carries a number, a date and the issuing laboratory's name. Before anything else, put that number into the lab's own online verification tool and compare what comes back against the paper or PDF in front of you. If the digital record and the document disagree on a single field, stop there.

The report number also matters because it is often laser-inscribed on the stone's girdle. GIA's laboratory-grown diamond service page states that "the laboratory-grown diamond's girdle is laser inscribed with 'Laboratory-Grown' and the GIA quality assessment number" (GIA, Laboratory-Grown Diamond Services, accessed September 2026). For natural stones, an inscription is standard on some report types and optional on others: GIA lists the Diamond Dossier® as including a "GIA report number laser inscription," while the Diamond Grading Report for stones 0.15 carats and up covers the "full 4Cs assessment with a plotted clarity diagram" (GIA, Natural Diamond Grading Reports & Services, accessed September 2026). An inscription lets a jeweller match paper to stone under a loupe. Ask for that check before setting.

Note the date, too. A report describes the stone on the day it was graded. A diamond that has been worn, chipped and repolished since then no longer matches its paperwork.

The top block: shape, measurements and carat weight

The upper section is descriptive rather than evaluative. Shape and cutting style ("round brilliant", "emerald cut"), then measurements. GIA lists a round diamond's dimensions as minimum diameter, maximum diameter, then depth; fancy shapes are listed as length by width by depth.

Measurements are the honest size check. Carat is weight, not spread. GIA defines it plainly: "A metric carat is defined as 200 milligrams," subdivided into 100 points, and weight "can be measured to the thousandth decimal place for rounding purposes" (GIA, Diamond Carat Weight, accessed September 2026). Two stones of identical weight can differ by half a millimetre face-up depending on how deep they are cut, and the millimetre figure is what a finger actually shows.

Weight also drives price in steps rather than a smooth line. GIA notes that "although it is difficult to visually distinguish a 0.99 carat diamond from a 1.00 carat, the price difference can be significant," and names 1.00, 1.50 and 2.00 carats as "magic sizes for their desirability." That is the single easiest saving on the page. Filtering our loose diamond search to 0.90–0.98 ct instead of 1.00 ct usually buys a better colour or cut grade for the same CAD budget, and nobody will measure it.

The four grades, and what each one actually means

Colour

The scale runs D to Z. GIA describes it as running "from D for colourless to Z for light" yellow, brown or grey, and states that proper evaluation needs "precise conditions, under controlled lighting, where stones are compared to masterstones with established colour grades" (GIA, Diamond Colour, accessed September 2026). Two points worth being blunt about: the grading is done face-down against masters, not face-up in a ring, and a single grade step is very hard to see once the stone is set in metal. Warm metals mask warmth in the stone, so a G or H in yellow gold looks like money well kept rather than money saved.

Clarity

Clarity is graded "under 10x magnification," and GIA distinguishes inclusions ("internal and surface reaching characteristics") from blemishes ("external features"). The published definitions are short and worth reading as written (GIA, Diamond Clarity, accessed September 2026):

  • FL — "No inclusions and no blemishes visible."
  • IF — "No inclusions visible but does have blemishes."
  • VVS1, VVS2 — "Inclusions so slight they are difficult for a skilled grader."
  • VS1, VS2 — "Inclusions are observed with effort but can be characterized as minor."
  • SI1, SI2 — "Inclusions are noticeable."
  • I1, I2, I3 — "Inclusions are obvious which may affect transparency, brilliance and durability."

Everything down to SI1 is describing what a trained grader sees at 10x, not what you see. That is why the clarity plot matters more than the letter grade, and why paying up from VS1 to VVS2 buys you paperwork.

Cut, polish and symmetry

GIA grades cut as "Excellent, Very Good, Good, Fair, or Poor," and for the top grade "a diamond must exhibit an even pattern of bright and dark areas." Polish is "the overall quality and condition of the facet surfaces"; symmetry "evaluates the exactness of the diamond's outline, and the shape, placement, and alignment of its facets." Both run Excellent to Poor (GIA, Understanding Diamond Cut Grades, accessed September 2026).

The limitation people miss: GIA issues an overall cut grade only for "standard round brilliant cut diamonds in the D-to-Z color range." An oval, pear or emerald cut gets polish and symmetry assessments and a proportions diagram, but no cut grade at all. For fancy shapes you are reading numbers and looking at the stone, not reading a verdict.

The diagram and the small print

The plotted diagram maps clarity characteristics by type and position. Read it for two things: whether an inclusion sits under the table where it is most visible, and whether anything reaches the surface at a point a setting will not protect. A feather at the girdle of a stone destined for a bezel is a different conversation from the same feather in a four-claw solitaire.

Below that sits the proportions diagram and then the comments. Comments are where a lab records anything that did not fit a box: additional clarity characteristics, surface graining, or a note on treatment. Read them before you read the grades again.

Fluorescence is its own line. GIA defines it as "the effect that ultraviolet (UV) light has on a diamond" and reports that roughly "25% to 35% exhibit some degree of fluorescence. However, only 10% of those show strengths of fluorescence that may affect appearance." Their observer research concluded that "the average person could not make a distinction between a diamond with fluorescence and a diamond without" (GIA, Understanding Diamond Fluorescence, accessed September 2026). Faint or medium blue fluorescence usually trades at a discount for no visible reason. That is a genuine saving, not a compromise.

Lab-grown reports read differently

Lab-grown stones are graded on the same colour and clarity scales, but the report must say what the stone is. GIA states that its "assessments for laboratory-grown diamonds have a distinct format to fully differentiate them from reports for natural diamonds."

The disclosure rules behind that are regulatory, not stylistic. The US FTC's Jewelry Guides require that terms such as "laboratory-grown" or "laboratory-created" appear immediately before the stone name "with equal conspicuousness," and the FTC has warned sellers against burying that disclosure behind links or FAQ pages (FTC, "Warning letters re 'mined' diamond sellers to describe products accurately," 2 April 2019). If a report or a listing is coy about origin, that is the finding, not a detail.

Growth method (CVD or HPHT) and any post-growth treatment belong in the comments. A colour-treated lab stone is a legitimate product, but it should be stated on the page.

What the report settles, and what it does not

Report fieldWhat it settlesWorth paying up for?
Carat weightExact weight to 0.001 ctOnly across a magic size; 0.95 ct looks like 1.00 ct
Measurements (mm)Face-up spread and depthYes, free information; compare against weight
Cut grade (rounds only)Even light and dark patternYes. The one grade that changes how it looks
Colour (D–Z)Position against masterstonesTo a point. One grade rarely shows once set
Clarity (FL–I3)What a grader sees at 10xNot above VS1 for most eyes
Polish / symmetryFacet surface and alignmentVery Good is fine; Excellent is not visibly better
FluorescenceReaction under UVNo. Often a discount with no visible cost
Comments / plotTreatments, position of inclusionsRead every time

Be clear about the limits. A report does not price the stone, does not say a stone is beautiful, and does not compare across labs. Different laboratories apply the same letters with different strictness, and there is no published conversion table between them, so comparing an SI1 from one lab against an SI1 from another is not a like-for-like comparison. Colour and clarity grading involve human judgement within defined tolerances, which is why a stone can sit one step either side of a boundary.

The report also covers only the stone. The metal is governed separately: in Canada, the Competition Bureau's guide to the Precious Metals Marking Act states that "it is not mandatory to mark or advertise a precious metal article for quality," but where a quality mark is applied "it must also bear a trade-mark that has either been applied for or registered with the Registrar of Trade-marks in Canada," with gold marking permitted from a minimum of 9K (Competition Bureau Canada, Guide to the Precious Metals Marking Act and Regulations, date modified 17 March 2025). So the mark inside your band and the report for your diamond answer two different questions.

Read it in this order

  1. Verify the report number on the lab's own site and confirm the grading date.
  2. Check measurements against carat weight to see how the stone will actually sit.
  3. Read cut, polish and symmetry first if it is a round; read proportions and look at the stone if it is not.
  4. Read the comments and the clarity plot before the colour and clarity letters.
  5. Only then compare price, and only against stones with reports from the same lab.

What to do next

Pick the look first, then the paperwork. Browse engagement ring settings to fix the shape and claw style you need, then filter the loose diamond search to that shape and pull up two or three reports side by side. Run the numbers above on each, preview them in 3D, then finish the ring with metal, size and engraving. If you want the grade-by-grade detail behind any single line on the report, the rest of our guides go deeper on colour, clarity and cut individually.

Sources