Diamond 4Cs calculator
See how carat, colour, clarity and cut trade off against each other. The index shows how price typically moves as each C changes, and the rarity panel counts how many stones in our own stock meet the specification. It teaches the shape of the market; it is not a quote.
Origin
Ticks mark weights where prices step up.
D is colourless; each step down shows a little more warmth.
FL has no inclusions under 10× magnification; I2 has obvious ones.
How well the facets return light. It does the most for sparkle.
Relative price index
100the reference stone
- Carat
- ×1.00
- Colour
- ×1.00
- Clarity
- ×1.00
- Cut
- ×1.00
Educational, not a quote. The index models how natural diamond prices typically move with each C, relative to a 1.00 ct, G, VS2, Excellent round (100). Lab-grown prices follow a similar pattern but at a far lower level and a much flatter curve between grades. Fluorescence, proportions and the market all move real prices.
Where the money goes
- Right on the 1.00 ct milestone. A 0.95 ct stone comes out 16% lower on the index and is only about 1% narrower face-up, which few people can see.
Rarity in our stock
245 of our 256 lab-grown round stones (D–J) are this size band, colour and clarity or better — about 96%. Stock is a snapshot, not the whole market, but the pattern is the same: every step up thins the field.
See these 245 stonesFace-up size, to scale
Approximate, at typical proportions.
4Cs and price
Which of the 4Cs affects diamond price the most?
Carat weight, because price per carat itself rises with size: a 2 carat stone typically costs far more than two 1 carat stones of the same grades. Colour and clarity come next, and cut matters most for how the stone actually looks.
Why do diamond prices jump at 1 carat?
Prices are set in weight bands, and demand clusters at round numbers such as 0.50, 1.00 and 2.00 carats. A stone just under a milestone, such as 0.95 carat, usually costs noticeably less and looks almost the same size.
Is this calculator a price quote?
No. It shows how prices typically move relative to a 1.00 carat, G, VS2, Excellent round, so you can see the trade-offs between the 4Cs. Real prices also depend on fluorescence, proportions, the grading laboratory and the market, and are quoted on enquiry.
Do the same rules apply to lab-grown diamonds?
The direction is the same (bigger, whiter and cleaner costs more), but lab-grown prices are much lower and the gaps between grades are much smaller, so a higher grade is usually a smaller step up.