A 3 carat round diamond is about 9.28 mm across. The same weight is 11.2 × 8.3 mm as an oval, 8.0 mm as a princess, 10.0 × 7.2 mm as an emerald cut and 15.1 × 7.6 mm as a marquise. Each cut is drawn at true 1:1 size on a finger below.
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| Actions | |||||||
|---|---|---|---|---|---|---|---|
| 9.28 | 1 : 1 | 5.71 | 67.7 | 56% | 49% | ||
| 11.25 × 8.33 | 1.35 : 1 | 5.16 | 73.6 | 50% | 44% | ||
| 10.02 × 7.16 | 1.4 : 1 | 4.65 | 69.1 | 43% | 38% | ||
| 12.78 × 7.98 | 1.6 : 1 | 4.95 | 71.8 | 48% | 42% | ||
| 8.82 × 8.01 | 1.1 : 1 | 5.21 | 66.3 | 49% | 42% | ||
| 8.02 | 1 : 1 | 5.62 | 64.4 | 49% | 42% | ||
| 15.11 × 7.55 | 2 : 1 | 4.53 | 79.8 | 46% | 40% | ||
| 9.53 × 7.63 | 1.25 : 1 | 5.03 | 71.0 | 46% | 40% |
| Actions | ||||
|---|---|---|---|---|
| 3.52 | 9.28 mm | 3.00 ct | ||
| 3.21 | 9.57 mm | 2.74 ct | ||
| 4.00 | 8.89 mm | 3.41 ct | ||
| 2.72 | 10.11 mm | 2.32 ct |
05 / Field guide
What 3 carat looks like in millimetres: every cut at standard proportions, on fingers of different sizes, against the weights either side and in other stones. Sizes are estimates from the trade formulas; a real stone varies with its cut.
3 carat is 600 mg. As a round brilliant at a 61.5% depth it is 9.28 mm across and about 5.71 mm deep. marquise (15.1 × 7.6 mm), oval (11.2 × 8.3 mm), pear (12.8 × 8.0 mm) spread the same weight over the largest outlines; the princess (8.0 mm) faces up smallest because more of its weight sits below the girdle.
Face-up, the marquise covers 79.8 mm² against 64.4 mm² for the princess, 24% more for the same 3 carats.
A 9.28 mm round covers about 59% of the width of a US 5 finger (15.7 mm), 54% of a US 7 and 47% of a US 10. It fills a good part of the finger without overhanging it. Set the finger chips to your own size to see it drawn at 1:1.
Up from 2.5 ct (8.73 mm), the stone is 6% wider. A 4 carat round is 10.22 mm, only 10% wider, because weight grows with the cube of the size.
Density changes the size of a stone of the same weight. 3 ct of moissanite (SG 3.21) is about 9.57 mm round, sapphire or ruby (SG 4.00) 8.89 mm and emerald (SG 2.72) 10.11 mm, against 9.28 mm for diamond. Moissanite is usually sold by diamond equivalent weight, so a “3 ct DEW” moissanite is cut to the 9.28 mm diamond size and weighs about 2.74 ct.
Questions
About 9.28 mm across as a round brilliant. As an oval it is about 11.2 × 8.3 mm, a princess 8.0 mm, an emerald cut 10.0 × 7.2 mm and a cushion 8.8 × 8.0 mm.
The marquise, at 15.1 × 7.6 mm with 79.8 mm² face-up. The princess looks smallest at 8.0 mm.
Sold by diamond equivalent weight, it is the diamond size, 9.28 mm round, and weighs about 2.74 ct. A moissanite weighing a true 3 ct is about 9.57 mm.
A 9.28 mm round covers about 56% of the 16.5 mm width of a US 6 finger.
As rounds, 10.22 mm against 9.28 mm: about 10% wider for 33% more weight.