“How big is 1 carat, really?” It is one of the questions jewellers hear most often. Carat is a weight, not a size. Yet customers want to know how big their stone will look on the hand.
In this overview you will find the usual dimensions in millimetres per carat, for round stones and for the most popular shapes.
1. Carat is weight, not size
One carat is 0.2 grams. The heavier the stone, the larger it usually is. But two stones of the same weight can still look different:
- Cut quality: a stone that is cut too deep hides its weight in the bottom and looks smaller.
- Shape: elongated shapes such as oval, pear and marquise look larger than a round stone of the same weight.
The sizes below are therefore guide values for well-proportioned stones. Actual dimensions vary by cut.
2. Round brilliant: carat and diameter
| Carat | Diameter |
|---|---|
| 0.25 ct | 4.1 mm |
| 0.50 ct | 5.2 mm |
| 0.75 ct | 5.9 mm |
| 1.00 ct | 6.5 mm |
| 1.25 ct | 7.0 mm |
| 1.50 ct | 7.4 mm |
| 2.00 ct | 8.2 mm |
| 2.50 ct | 8.8 mm |
| 3.00 ct | 9.3 mm |
| 4.00 ct | 10.2 mm |
| 5.00 ct | 11.0 mm |
Worth noting: a 2 carat stone is twice as heavy as a 1 carat stone, but its diameter is only about a quarter larger. That is useful to explain to customers.
3. Fancy shapes: dimensions per carat
For elongated shapes we give length and width.
| Shape | 0.5 ct | 1 ct | 1.5 ct | 2 ct | 3 ct |
|---|---|---|---|---|---|
| Oval | 6.0 × 4.0 | 7.7 × 5.7 | 8.5 × 6.5 | 9.5 × 7.0 | 11.0 × 8.0 |
| Princess | 4.4 | 5.5 | 6.3 | 7.0 | 8.0 |
| Cushion | 5.0 | 6.0 | 6.9 | 7.5 | 8.5 |
| Emerald | 6.0 × 4.0 | 7.0 × 5.0 | 8.0 × 6.0 | 8.5 × 6.5 | 9.5 × 7.5 |
| Radiant | 5.0 × 4.5 | 6.5 × 5.5 | 7.5 × 6.0 | 8.0 × 6.5 | 9.0 × 7.5 |
| Pear | 6.0 × 4.0 | 8.0 × 5.0 | 9.0 × 6.0 | 10.0 × 6.5 | 12.0 × 7.5 |
| Marquise | 8.0 × 4.0 | 10.0 × 5.0 | 12.0 × 6.0 | 13.0 × 6.5 | 15.0 × 7.5 |
All sizes in millimetres. For princess and cushion, the figure is the width of a square stone.
4. Which shape looks largest?
At the same weight, elongated shapes look larger because they have more surface area on top:
- Marquise looks the largest per carat
- Pear and oval follow
- Round, princess and cushion look more compact, but give a lot of sparkle
For customers who want a large stone within their budget, an oval is often a strong choice.
5. Tip: show it, don't just tell it
Customers find millimetres hard to picture. An actual-size chart, or a transparent card you place on the hand or on a setting, makes the difference clear immediately. Customers then often choose a larger stone than they expected.
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