The 4Cs of diamonds
How every diamond is graded, and how to balance them for your budget.
From the CTJ Jewellery team, led by founder Greg Ward
Cut, colour, clarity and carat are the grading language used by laboratories such as GIA and IGI. Most people don’t ask for a particular grade.
They want the best-looking diamond for their budget. We start with visual performance, then balance the four Cs to get the most value.
Cut
Cut is the proportions, symmetry and polish of a diamond, which together decide its brightness, fire and sparkle. It is not the same as shape.
- Excellent
- Maximum brightness, fire and sparkle. Light enters, reflects and returns through the top.
- Very good
- Close to excellent. The difference shows side by side, rarely on the hand.
- Good
- Noticeably less sparkle. Some light escapes through the sides or base.
- Fair
- Dull in all but bright light.
- Poor
- Most light is lost.
Cut quality comes first. It does more for how a diamond looks than any other grade.
Colour
White diamonds are graded D to Z by the absence of colour. D is completely colourless. Neighbouring grades are very hard to tell apart by eye.
- D, E, F · Colourless
- No detectable colour, even to a grader. The rarest range.
- G, H · Near colourless
- Colour visible only face-down against a master stone. A popular balance in platinum and white gold.
- I, J · Near colourless
- A faint warmth in larger stones. Excellent value in yellow and rose gold.
- K, L, M · Faint
- A visible warm tint, sometimes chosen for vintage and yellow-gold pieces.
- N to Z · Light
- Clearly yellow or brown.
Match colour to the metal. White metals show colour most clearly, while yellow and rose gold warm the diamond anyway.
Clarity
Almost every diamond has tiny internal features called inclusions. Clarity grades how many there are, how large, and whether you can see them.
- FL · Flawless
- No inclusions or blemishes under 10× magnification. Exceptionally rare.
- IF · Internally flawless
- No inclusions under 10×, only minor surface blemishes.
- VVS1, VVS2
- Inclusions so small a skilled grader struggles to find them at 10×.
- VS1, VS2
- Minor inclusions visible only at 10× magnification.
- SI1, SI2
- Noticeable at 10×. Many SI1 diamonds are still eye-clean, so each needs checking.
- I1, I2, I3 · Included
- Inclusions visible to the eye that can affect brilliance and durability.
An eye-clean diamond. Beyond that point you pay for clarity you can’t see, so we check each diamond in person.
Carat
Carat is weight, not size. One carat is 0.2 grams.
How large a diamond looks also depends on its shape and cut. For jewellery with more than one diamond, weight is given as TDW, the total diamond weight.
- 0.25ct
- About 4.1 mm across
- 0.50ct
- About 5.1 mm
- 0.75ct
- About 5.8 mm
- 1.00ct
- About 6.5 mm
- 1.50ct
- About 7.4 mm
- 2.00ct
- About 8.2 mm
- 3.00ct
- About 9.3 mm
The size that suits the hand and the budget. A diamond just under a round weight, such as 0.95ct, looks the same as 1.00ct.