Why a 0.9 Carat Diamond Costs Much Less Than a 1 Carat

Diamond price per carat rises in steps, not a straight line. Why the jump at one carat exists, how little size you give up at 0.9 and how to shop below it.

Diamonds are priced per carat, and the diamond price per carat is not a smooth curve. It climbs in steps, and the steepest steps sit at the weights people ask for by name: half a carat, one carat, one and a half, two. A stone weighing 0.90 carat and a stone weighing 1.00 carat, otherwise identical, can differ in price by far more than the ten percent of weight that separates them.

How the trade prices weight

Wholesale diamond prices are organised in weight brackets. Stones from 0.90 to 0.99 carat sit in one bracket; stones from 1.00 to 1.49 carat sit in the next. Each bracket has its own per-carat rate, and the rate jumps at the boundary.

This is partly supply. Cutters work hard to keep a rough stone above a magic weight, because the finished stone will sell for more. That means fewer stones land at 0.95 than the natural distribution would suggest, and more land at exactly 1.00 or 1.01. It is also partly demand. One carat is a milestone. People want to be able to say it.

The combined effect is a price cliff. The buyer pays for the number, and the number is on the report.

What you actually give up

A well-cut one carat round measures about 6.4 to 6.5 mm across. A well-cut 0.90 carat round measures about 6.2 to 6.3 mm. The difference is around 0.2 mm, which is thinner than a fingernail. On a hand, at normal viewing distance, it is not detectable.

The same applies at other thresholds. A 0.45 carat against a 0.50, a 1.40 against a 1.50, a 1.90 against a 2.00. In each case the visible difference is a fraction of a millimetre and the price difference is a bracket.

The cutting trap on the other side

There is a second reason to be wary of the round number itself. Because the price reward for reaching 1.00 carat is so large, some cutters will accept worse proportions to get there. A stone that could have been a beautifully cut 0.95 becomes a slightly deep, slightly thick-girdled 1.00. It weighs more and looks smaller, because the extra weight is hidden in the pavilion where nobody sees it.

So a 1.00 carat stone deserves a closer look at its depth percentage and girdle thickness than a 0.90 does. The 0.90 was probably cut for beauty. The 1.00 may have been cut for weight.

How to shop the gap

Ask for stones between 0.85 and 0.98 carat rather than "about one carat". A jeweller who sources loose stones can search that band directly.

Compare the millimetre measurements, not the carat figures. Two stones with the same diameter look the same size regardless of what they weigh.

Check the cut grade and proportions. The saving is only real if the smaller stone is at least as well cut.

Put the saving somewhere visible. The difference between brackets can fund a step up in colour, a better cut grade, or a heavier setting that will last longer.

Accept that the report will say 0.9x. If the number matters to you or to the person receiving the ring, that is a legitimate preference and worth paying for. Just make the decision knowingly.

The wider lesson

The pattern repeats at every level. Prices step up at colour boundaries, at clarity boundaries and at weight boundaries, because the trade organises itself around those lines. The stones just below each line are consistently the best value in the market, and the stones just above are consistently the worst. Buying well is largely a matter of knowing where the lines are.

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C'Garden is an independent bespoke jeweller in Kuala Lumpur. We are not affiliated with, endorsed by, sponsored by or certified by any organisation, laboratory or brand named in this article. Third-party names are used only to refer factually to those organisations and their published standards. All text and imagery in this article is original work created by C'Garden.

Reference

Gemological Institute of America. (n.d.). Diamond carat weight. GIA. https://www.gia.edu/diamond-carat-weight