A 4 carat round diamond is about 10.22 mm across. The same weight is 12.4 × 9.2 mm as an oval, 8.8 mm as a princess, 11.0 × 7.9 mm as an emerald cut and 16.6 × 8.3 mm as a marquise. Each cut is drawn at true 1:1 size on a finger below.
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| Actions | |||||||
|---|---|---|---|---|---|---|---|
| 10.22 | 1 : 1 | 6.28 | 82.0 | 62% | 54% | ||
| 12.38 × 9.17 | 1.35 : 1 | 5.68 | 89.1 | 56% | 48% | ||
| 11.03 × 7.88 | 1.4 : 1 | 5.12 | 83.6 | 48% | 42% | ||
| 14.06 × 8.79 | 1.6 : 1 | 5.45 | 87.0 | 53% | 46% | ||
| 9.70 × 8.82 | 1.1 : 1 | 5.73 | 80.4 | 53% | 47% | ||
| 8.83 | 1 : 1 | 6.18 | 78.0 | 53% | 47% | ||
| 16.63 × 8.31 | 2 : 1 | 4.99 | 96.6 | 50% | 44% | ||
| 10.49 × 8.39 | 1.25 : 1 | 5.54 | 86.0 | 51% | 44% |
| Actions | ||||
|---|---|---|---|---|
| 3.52 | 10.22 mm | 4.00 ct | ||
| 3.21 | 10.53 mm | 3.65 ct | ||
| 4.00 | 9.79 mm | 4.55 ct | ||
| 2.72 | 11.13 mm | 3.09 ct |
05 / Field guide
What 4 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.
4 carat is 800 mg. As a round brilliant at a 61.5% depth it is 10.22 mm across and about 6.28 mm deep. marquise (16.6 × 8.3 mm), oval (12.4 × 9.2 mm), pear (14.1 × 8.8 mm) spread the same weight over the largest outlines; the princess (8.8 mm) faces up smallest because more of its weight sits below the girdle.
Face-up, the marquise covers 96.6 mm² against 78.0 mm² for the princess, 24% more for the same 4 carats.
A 10.22 mm round covers about 65% of the width of a US 5 finger (15.7 mm), 59% of a US 7 and 52% 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 3 ct (9.28 mm), the stone is 10% wider. A 5 carat round is 11.00 mm, only 8% wider, because weight grows with the cube of the size.
Density changes the size of a stone of the same weight. 4 ct of moissanite (SG 3.21) is about 10.53 mm round, sapphire or ruby (SG 4.00) 9.79 mm and emerald (SG 2.72) 11.13 mm, against 10.22 mm for diamond. Moissanite is usually sold by diamond equivalent weight, so a “4 ct DEW” moissanite is cut to the 10.22 mm diamond size and weighs about 3.65 ct.
Questions
About 10.22 mm across as a round brilliant. As an oval it is about 12.4 × 9.2 mm, a princess 8.8 mm, an emerald cut 11.0 × 7.9 mm and a cushion 9.7 × 8.8 mm.
The marquise, at 16.6 × 8.3 mm with 96.6 mm² face-up. The princess looks smallest at 8.8 mm.
Sold by diamond equivalent weight, it is the diamond size, 10.22 mm round, and weighs about 3.65 ct. A moissanite weighing a true 4 ct is about 10.53 mm.
A 10.22 mm round covers about 62% of the 16.5 mm width of a US 6 finger.
As rounds, 11.00 mm against 10.22 mm: about 8% wider for 25% more weight.