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Diamond Carats: The Expert Guide
Diamond carat weights are one of the most misunderstood aspects of buying a diamond. Often confused with size, the carat actually refers to weight. Here at Diamond Heaven, we’ll explain what that means in terms of appearance and value.
One carat, two different diamonds
Because carat weight is not determined by dimensions alone, two 1‑carat diamonds can look completely different. This is because the weight is distributed throughout the entire stone, not just on the surface.
WHAT IS CARAT?
Carat refers to the weight of a diamond. Diamonds are weighed in metric carats rather than grams or ounces
Diamond carats aren’t limited to whole numbers; they are measured in points. A helpful comparison is pounds and pence. Just as 100p = £1, 100 points = 1ct.
If you wanted to convert a diamond carat weight into grams, simply multiply the carat by 0.2.
- 1ct - 0.2g
- 2.5ct - 0.5g
Carat weight Vs carat size
Carat refers to weight, not visible size. Two diamonds with the same carat weight may appear different depending on cut, proportions and shape.
We always recommend trying on a range of carat weights to determine which looks best on your hand. Different diamond shapes can appear larger or smaller depending on their proportions and cut, which is why we’ve created the following chart as a guide to typical measurements.
| Carat Weight | 0.25ct | 0.50ct | 0.75ct | 1ct | 1.50ct | 2ct | 3ct | 4ct | 5ct | Carat Weight | |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Round |  |
4mm | 5mm | 5.50mm | 6.50mm | 7.50mm | 8mm | 9.40mm | 10.40mm | 11.20mm | |
| Princess |  |
3.50mm | 4.50mm | 5mm | 5.50mm | 6.80mm | 7.50mm | 8mm | 8.90mm | 9.70mm | |
| Heart |  |
4x4mm | 5x5mm | 6x6mm | 6.50x6.50mm | 7x7mm | 8x8mm | 9x9mm | 10x10mm | 11x11mm | |
| Emerald |  |
4x3mm | 6x4mm | 6.50x4.50mm | 7x5mm | 8x6mm | 8.50x6.50mm | 10x8mm | 11x9mm | 10x10mm | |
| Asscher |  |
3.70mm | 4.40mm | 5mm | 5.80mm | 6.40mm | 7mm | 8.10mm | 9mm | 9.60mm | |
| Marquise |  |
5x3mm | 8x4mm | 9x4.50mm | 10x4.75mm | 11x5mm | 12x6mm | 14x7mm | 15x7mm | 16x8mm | |
| Radiant |  |
3.50x3mm | 5x4.50mm | 5.50x5mm | 6x5.50mm | 7x6mm | 7.50x7mm | 8.50x7.50mm | 9.50x8.50mm | 10x9mm | |
| Cushion |  |
4x3.50mm | 5x4.50mm | 6x5mm | 6.50x5.50mm | 7.50x6.50mm | 8x7mm | 9x8mm | 10x8.50mm | 10x9.50mm | |
| Oval |  |
5x3mm | 6x4mm | 7x5mm | 7.50x5.50mm | 8.50x6.50mm | 9x7mm | 10x8mm | 11x9mm | 12x10mm | |
| Pear |  |
4x2mm | 6x4mm | 7x5mm | 8x5mm | 9x6mm | 10x7mm | 12x8mm | 14x9mm | 15x10mm | |
How to choose the right carat weight
1. The budget
Larger carat weights automatically increase the cost of a diamond. Choosing a lab‑grown diamond can make it possible to select a larger carat size at a lower cost.
Milestone weights, such as 0.50ct and 1.00ct, are often significantly more expensive than slightly smaller stones (e.g., 0.40ct or 0.90ct), despite looking very similar in size.
2. The cut
A well‑cut 0.90ct diamond can look brighter and more impressive than a poorly cut 1.00ct diamond.
For example, if a stone is cut too deeply, it may have a higher carat weight, but some of that weight will sit in the pavilion, making the diamond appear smaller when viewed from above.
Conversely, a shallow cut maximises surface area but allows light to leak from the stone, resulting in less sparkle.
3. The shape
Different diamond shapes carry weight differently.
- Oval, marquise and pear cuts naturally appear larger because of their elongated shape.
- Emerald and asscher cuts require more depth to achieve their “hall of mirrors” effect, which can make them appear slightly smaller face‑up
4. The setting
Choosing a halo or shoulder‑set ring can enhance the overall visual impact of your engagement ring without needing to increase the carat weight of the centre stone.
See the difference in person
The best way to truly understand how carat weight affects your diamond is to compare different weights side by side. Visit Diamond Heaven for expert advice or book an appointment for a personalised consultation today. [email protected] or 0345 222 5009.
