Introduction
A diamond grading report is a dense document. It compresses weeks of laboratory work — measurement, observation, comparison against master stones, light-performance assessment — into a single page. For buyers encountering one for the first time, the volume of data can feel overwhelming: numbers, grades, diagrams, and abbreviations crowded into a small space.
This article walks through each section of a standard diamond grading report, explains what information it contains, and clarifies why that information matters. The GIA Diamond Grading Report serves as our reference layout, since it is the most widely recognised format in international markets and the Czech Republic alike. HRD Antwerp and IGI follow similar structures with minor differences in labelling, which are noted where relevant.
If you are unsure whether the document you are looking at is technically a report or a certificate, see Report vs Certificate for the distinction.
Report Header and Identification
The top of every grading report establishes three things: which laboratory issued it, when the examination took place, and which specific stone the report describes.
Report number
Every report carries a unique number that links the document to a specific diamond in the laboratory's database. On GIA reports, this number is also laser-inscribed on the diamond's girdle, allowing you to match stone to document. See Report Number & Inscription for details on verification.
Date
The date records when the diamond was examined. Grading reflects the stone's condition at that moment. If a diamond is re-cut, re-polished, or damaged after the report date, the grades may no longer apply.
Shape and cutting style
The report identifies the diamond's shape — round brilliant, oval, cushion, emerald, and so on — and its cutting style (brilliant, step, mixed). This classification determines which grading criteria apply. GIA assigns a formal cut grade only to standard round brilliants; fancy shapes receive proportions and finish assessments but no overall cut grade.
Carat Weight
Carat weight is recorded to the hundredth of a carat (e.g., 1.52 ct). Laboratories use calibrated electronic scales with a precision of 0.001 ct, rounding to the second decimal place using specific protocols. A diamond that weighs 1.498 ct is recorded as 1.49 ct; only when the third decimal reaches 9 — as in 1.499 ct — does it round up to 1.50 ct.
This section is straightforward but consequential. Price per carat increases at certain thresholds — 0.50, 1.00, 1.50, 2.00 ct — so even a 0.01 ct difference can affect market value.
Measurements
Dimensions are recorded in millimetres. For round brilliants, reports list the minimum and maximum diameter plus the total depth (e.g., 7.38–7.42 × 4.56 mm). For fancy shapes, the report records length, width, and depth.
These figures let you calculate the diamond's visual spread — how large it appears when viewed from above — relative to its carat weight. Two diamonds of identical weight can differ meaningfully in face-up size depending on their proportions. See Measurements and Spread & Face-Up Size for more on this relationship.
The 4Cs Grades
The central section of any grading report presents the four grades that most buyers focus on.
Colour grade
For diamonds in the normal colour range (colourless to light yellow or brown), GIA uses a D-to-Z alphabetical scale. D is colourless; Z shows noticeable colour. The grade is determined by comparing the diamond face-down against a set of master comparison stones under controlled lighting. See How Colour Is Graded for the methodology.
Clarity grade
Clarity is assessed on an 11-point scale from Flawless (FL) to Included (I3), based on the visibility of inclusions and blemishes under 10× magnification. The grade reflects the size, number, position, nature, and relief of clarity characteristics. See GIA Clarity Scale for definitions of each grade.
Cut grade (round brilliants only)
GIA assigns cut grades from Excellent to Poor based on a combination of proportions, light performance (brightness, fire, scintillation), design factors, and craftsmanship. This grade appears only on standard round brilliant reports. For fancy shapes, evaluate proportions and finish grades together. See Cut Grade Scale for what each grade means in practice.
Carat weight
Listed again in the grades section for reference, matching the measurement recorded above.
Finish Grades
Finish describes the quality of the diamond's surface and the precision of its facet alignment. It is assessed in two components.
Polish
Polish grades range from Excellent to Poor. They reflect the condition of the diamond's facet surfaces — whether they are smooth and well-finished or show wheel marks, scratches, or other polishing artefacts. See Polish for details.
Symmetry
Symmetry grades (Excellent to Poor) assess how precisely the facets align and intersect. Misaligned facets, off-centre tables, and wavy girdles all lower the symmetry grade. See Symmetry for the specific variations gemologists evaluate.
GIA groups polish and symmetry under "finish" but HRD and IGI present them in the same section with identical grade ranges.
Fluorescence
The report records the diamond's reaction to long-wave ultraviolet (UV) light, graded from None to Very Strong. If fluorescence is present, the report also notes the fluorescence colour — most commonly blue, though yellow, green, and other colours occur.
Fluorescence is neither inherently good nor bad. In some diamonds, strong blue fluorescence can cause a milky appearance; in others, it can make a slightly tinted stone appear whiter in daylight. See Fluorescence and Fluorescence: Helps vs Hurts for guidance on when it matters.
Clarity Plot
The clarity plot is a schematic diagram of the diamond showing the location, size, and type of each inclusion and blemish observed during grading. Red symbols represent internal characteristics (inclusions); green symbols represent external characteristics (blemishes).
This is one of the most informative sections of the report, yet many buyers skip it. The plot tells you not just the clarity grade but where the inclusions are — whether they sit under the table where they are most visible, near the girdle where they are easily hidden by a setting, or in a position that might affect durability. See Plot and Comments for how to read the diagram.
GIA, HRD, and IGI all include clarity plots, though the symbol conventions differ slightly between laboratories.
Proportions Diagram
The proportions diagram displays the diamond's key angles and percentages in a cross-section view:
- Table percentage — the width of the top facet relative to the girdle diameter
- Crown angle — the angle between the crown facets and the girdle plane
- Pavilion angle — the angle between the pavilion facets and the girdle plane
- Total depth percentage — the height of the diamond relative to its width
- Girdle thickness — described as a range (e.g., "Thin to Medium")
- Culet size — typically "None" (pointed) or "Very Small" to "Large"
These measurements are not decoration. Crown angle and pavilion angle together determine how efficiently the diamond returns light. Small deviations can meaningfully affect brightness and fire. See Proportions Primer for how to interpret these numbers.
Comments
The comments section contains additional observations that do not fit neatly into the grading fields. Common entries include:
- "Minor details of polish are not shown" — standard on most reports
- "Additional clouds are not shown" — indicates cloud inclusions beyond those plotted, which may affect transparency
- "This diamond has been treated by…" — discloses any known treatments (laser drilling, fracture filling, HPHT processing)
- Inscription details — confirms what is laser-inscribed on the girdle
Read the comments section carefully. The note "additional clouds are not shown" in particular can signal a transparency concern that the clarity grade alone does not communicate. See Cloud Inclusions & Transparency for context.
Security Features
Modern grading reports include multiple anti-fraud features: holograms, microprint lines, QR codes linked to the laboratory's database, and unique paper or card stock. GIA reports can be verified online using the report number at GIA's Report Check service. HRD and IGI offer similar online verification tools. See Online Report Verification for instructions.
Summary
A diamond grading report is a structured record of everything the laboratory observed and measured. Its core sections — identification, carat weight, measurements, the 4Cs grades, finish, fluorescence, clarity plot, proportions diagram, and comments — give you a complete technical profile of the stone. The clarity plot and proportions diagram deserve more attention than most buyers give them: the plot shows where inclusions sit, and the proportions reveal how the diamond handles light. GIA, HRD, and IGI organise their reports similarly, so understanding one layout prepares you for all three. Use the report as a map of the diamond's characteristics, then verify with your own eyes. For a broader introduction to how laboratories work and what their reports mean, continue to Reports 101.