Diamond Quality Chart: How to Read Cut, Colour & Clarity Grades (2026)
Last Updated: September 12, 2026
Quick Answer
A diamond is graded on four scales. Colour runs D (colourless) to Z (light yellow); the best value is G to I, which looks white in a setting. Clarity runs Flawless (FL) to Included (I3); VS1 to VS2 is eye-clean for far less than flawless. Cut is graded Excellent to Poor and matters most, since it drives sparkle. Carat is weight, not size: one carat is 0.2 grams, and a well-cut one-carat round measures about 6.5mm across. The best-value diamond for most buyers is an Excellent-cut, G-H colour, VS1-VS2 clarity stone.
Table of Contents
This is the quick-reference version: the grade scales as charts, what each grade means at a glance, and honest guidance on where a diamond is worth paying for and where it is not. For the full narrative on how the 4Cs work together, read our 4Cs of diamonds guide; this page is the chart you check while you shop.
What is a carat?
A carat is a unit of weight, not size. One carat equals 0.2 grams, and it is divided into 100 points, so a "50-point" diamond is half a carat. That is the single most misunderstood term in diamond buying, because two stones of the same carat weight can look quite different in size depending on how they are cut.
Do not confuse carat (diamond weight) with karat (gold purity, as in 14K). They sound identical and mean completely different things. How large a given carat weight looks on the finger depends on the shape and the cut, which is what the size chart further down shows.
The colour scale: D to Z
Diamond colour is graded on how little colour a stone has, from D (completely colourless) down to Z (noticeably tinted yellow or brown). Counterintuitively, less colour means a higher grade and a higher price.
| Grade | Category | What you see |
|---|---|---|
| D, E, F | Colourless | No colour at all; the rarest and priciest |
| G, H, I, J | Near-colourless | Looks white face-up, especially once set; the value sweet spot |
| K, L, M | Faint | A warm tint becomes visible, flatters yellow gold |
| N to Z | Very light to light | Clearly tinted; rarely used in fine jewellery |
For most buyers, G to I is the smart choice: it looks white to the eye at a fraction of the price of D-E-F. A warmer stone can look whiter set in yellow or rose gold, so metal colour lets you drop a grade.
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The clarity scale: FL to I3
Clarity grades how free a diamond is of inclusions (internal marks) and blemishes (surface marks), viewed under 10x magnification. The scale runs from Flawless down to Included.
| Grade | Meaning | What you see |
|---|---|---|
| FL / IF | Flawless / Internally Flawless | No inclusions under 10x; rare and expensive |
| VVS1 / VVS2 | Very Very Slightly Included | Inclusions extremely hard to see even under magnification |
| VS1 / VS2 | Very Slightly Included | Eye-clean; inclusions need magnification to spot; the value sweet spot |
| SI1 / SI2 | Slightly Included | May be eye-clean at SI1; inclusions easier to find |
| I1 / I2 / I3 | Included | Inclusions visible to the naked eye; avoid for a centre stone |
VS1 to VS2 is where most of the value sits: it is eye-clean, so the stone looks flawless without a loupe, at a large saving over an actual flawless grade. Paying for FL or IF is paying for something only a jeweller's microscope can appreciate. Our guide to reading a grading report shows how inclusions are plotted.
The cut grade scale
Cut is the most important of the four, because it decides how much light the diamond returns as sparkle, and it is the only C that is entirely down to human skill rather than nature. It is graded on proportions, symmetry and polish.
| Grade | What it means |
|---|---|
| Excellent / Ideal | Maximum light return; the stone looks alive. Worth prioritising. |
| Very Good | Nearly as bright as Excellent for slightly less; a sensible floor. |
| Good | Noticeably less brilliant; light leaks from the bottom. |
| Fair / Poor | Dull and lifeless; avoid regardless of the other grades. |
The rule that saves the most money and disappointment: never drop below Very Good on cut, and prefer Excellent. A well-cut stone one grade lower on colour or clarity will outshine a poorly cut stone that scores higher on paper. Spend on cut first.
Carat to size in millimetres
Because carat is weight, the more useful number when picturing a stone is its diameter. This is the approximate face-up size of a well-cut round diamond at each weight.
| Carat | Round diameter |
|---|---|
| 0.25 ct | ~4.1 mm |
| 0.50 ct | ~5.1 mm |
| 0.75 ct | ~5.8 mm |
| 1.00 ct | ~6.5 mm |
| 1.50 ct | ~7.4 mm |
| 2.00 ct | ~8.1 mm |
| 3.00 ct | ~9.3 mm |
Elongated shapes such as oval and marquise look larger than a round of the same weight because they spread across more of the finger. Our carat size guide shows each shape at each weight.
What a diamond is worth
"How much is a one-carat diamond worth" has no single answer, because the price depends on all four Cs at once, not carat alone. A poorly cut, tinted, included one-carat stone and a top-grade one-carat stone can differ several times over in price. And there are two entirely separate markets: mined and lab-grown.
Here is the honest, useful version, our live lab-grown starting prices by centre-stone weight, all IGI-certified and set in solid gold:
| Centre stone | Lab-grown ring from |
|---|---|
| 1 carat | Around $600-$900 depending on shape |
| 2 carat | From $1,288 |
| 3 carat | Higher again, still a fraction of mined |
A comparable mined diamond typically costs several times more for the same grades, which is the whole reason lab-grown has taken over the market. One thing to be clear-eyed about: diamonds of any origin resell poorly against retail, so a diamond is a purchase to wear and keep, not an investment. Anyone quoting you a resale "value" is selling you something. For the full picture see lab-grown vs natural diamonds.
As for the famous stones people ask about, the Hope and the Cullinan, they are historic, one-of-a-kind museum pieces whose value runs to the hundreds of millions and is essentially theoretical; they are not a useful guide to what a diamond you can actually buy is worth.
The best-value grades
Pulling the charts together, here is the combination that gives the most diamond for the money, the grades to aim for rather than the maximums:
- Cut: Excellent, or Very Good at the lowest. This is the one to prioritise.
- Colour: G to H for white metals; H to I is fine in yellow or rose gold.
- Clarity: VS1 to VS2, eye-clean without paying for flawless.
- Carat: buy just under a round number (1.9ct instead of 2.0ct) to save, since prices jump at the round figures.
Every Riona diamond is lab-grown and IGI-certified, so you can check these grades on the report for any stone. The saving over mined is what lets most of our customers move up a size or a grade rather than pay for a name.
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Frequently asked questions
What is a carat?
What is the best diamond colour and clarity for value?
How much is a 1 carat diamond worth?
What is the diamond quality chart order?
Do lab-grown diamonds use the same quality chart?
Are lab-grown diamonds worth it?
Does carat mean size?
Every Grade, on the Certificate
Every Riona diamond is lab-grown and IGI-certified, with its full colour, clarity, cut and carat grades on the report. Engagement rings from $1,288. Free express shipping, 30-day free returns.