Why Two Diamonds of the Same Carat Cost Different

It is a common moment of confusion. You are shown two diamonds, both of 0.50 carat, with prices that differ by a large amount. Neither seller is necessarily wrong. Carat is only the weight, and weight is only one of many things that decide price.

The 4Cs together

A diamond's price is built from its qualities:

• Cut: a stone with excellent proportions returns more light and is valued above one with an average cut.
• Colour: a stone nearer the colourless end of the scale is priced higher. See diamond colour grades D to Z.
• Clarity: fewer and smaller inclusions are priced higher. See diamond clarity: VS, SI and VVS.
• Carat: the weight, with price rising faster than weight as stones get larger.

Two stones with the same carat but different grades in the other three will be priced differently.

Shape

Round brilliants usually carry a higher price per carat than other shapes. A pear or an oval of the same weight and quality is often priced lower. See diamond shapes guide.

Certification

A stone graded by a well-regarded laboratory is typically priced with confidence in its grades. A stone with no report, or one graded by a lab with looser standards, may be priced lower, but you have less certainty about what you are paying for. See what diamond grading labs actually do.

Fluorescence and finish

Strong fluorescence can reduce a stone's price in some grades. Polish and symmetry also count. See diamond fluorescence explained and polish and symmetry.

Whether it looks its weight

A shallow or "spread" cut may look larger face-up than its weight suggests, while a deep one looks smaller. Buyers sometimes pay a premium for a stone that looks large. Compare the millimetre measurements on the certificate.

Whole-number effects

Prices jump at weights such as 0.50 and 1.00 carat. A stone at 0.49 is nearly the same size and often cheaper.

The seller's costs and margin

Retail prices include the seller's costs, such as showroom, staff, stock and service, and margin. These differ between sellers, which is why the same stone may be priced differently in two shops.

Market conditions

The wholesale price of diamonds changes with supply and demand. Prices for a given quality can move over time, so a price you were quoted last year may not hold today.

How to compare fairly

Make a table with these columns for each stone: shape, carat, colour, clarity, cut, polish, symmetry, fluorescence, laboratory and measurements. If the columns match and the prices differ, you have found a real difference in the seller's price. If the columns differ, the prices make sense.

Ask for the report

Always compare the certificates, not only the descriptions. See how to read a diamond certificate step by step.

Seeing the difference

Photos cannot show you why two stones are priced differently. Book an appointment to see two stones of equal weight side by side, or browse our diamond rings to see how each is described.