Free tool
Carat is weight, not size
Two one carat stones can look very different, because carat measures what a stone weighs and your eye measures what it covers.
Drawn to scale on screen at a nominal 96 pixels per inch. Your display may be a little off, so treat it as a close guide rather than a ruler.
Carat to millimetres, every cut
Face-up size for each weight. Dimensions scale with the cube root of carat, which is why a 2.00ct stone is about a quarter wider than a 1.00ct rather than twice the size.
| Carat | Round brilliant | Oval | Emerald cut | Cushion | Pear | Princess | Wider than 0.50ct |
|---|---|---|---|---|---|---|---|
| 0.25 | 4.09 × 4.09 | 4.85 × 3.59 | 4.41 × 3.15 | 3.78 × 3.78 | 5.04 × 3.15 | 3.46 × 3.46 | -21% |
| 0.33 | 4.49 × 4.49 | 5.32 × 3.94 | 4.84 × 3.46 | 4.15 × 4.15 | 5.53 × 3.46 | 3.80 × 3.80 | -13% |
| 0.50 | 5.16 × 5.16 | 6.11 × 4.52 | 5.56 × 3.97 | 4.76 × 4.76 | 6.35 × 3.97 | 4.37 × 4.37 | Base |
| 0.70 | 5.77 × 5.77 | 6.84 × 5.06 | 6.22 × 4.44 | 5.33 × 5.33 | 7.10 × 4.44 | 4.88 × 4.88 | 12% |
| 0.90 | 6.28 × 6.28 | 7.43 × 5.50 | 6.76 × 4.83 | 5.79 × 5.79 | 7.72 × 4.83 | 5.31 × 5.31 | 22% |
| 1.00 | 6.50 × 6.50 | 7.70 × 5.70 | 7.00 × 5.00 | 6.00 × 6.00 | 8.00 × 5.00 | 5.50 × 5.50 | 26% |
| 1.25 | 7.00 × 7.00 | 8.29 × 6.14 | 7.54 × 5.39 | 6.46 × 6.46 | 8.62 × 5.39 | 5.92 × 5.92 | 36% |
| 1.50 | 7.44 × 7.44 | 8.81 × 6.52 | 8.01 × 5.72 | 6.87 × 6.87 | 9.16 × 5.72 | 6.30 × 6.30 | 44% |
| 2.00 | 8.19 × 8.19 | 9.70 × 7.18 | 8.82 × 6.30 | 7.56 × 7.56 | 10.08 × 6.30 | 6.93 × 6.93 | 59% |
| 2.50 | 8.82 × 8.82 | 10.45 × 7.74 | 9.50 × 6.79 | 8.14 × 8.14 | 10.86 × 6.79 | 7.46 × 7.46 | 71% |
| 3.00 | 9.37 × 9.37 | 11.11 × 8.22 | 10.10 × 7.21 | 8.65 × 8.65 | 11.54 × 7.21 | 7.93 × 7.93 | 82% |
Carat questions
- How big is a 1 carat diamond in millimetres?
- A one carat round brilliant is about 6.5mm across. Carat is a measure of weight rather than size, so the same weight in a different cut looks quite different: a one carat oval reads noticeably larger than a one carat round because more of its weight sits at the surface.
- Does a bigger carat always look bigger?
- No. An elongated cut such as oval, marquise or pear spreads its weight across a wider face, so it looks larger than a round of the same weight. A deep-cut stone hides weight in its depth and can look smaller than a shallower stone weighing less.
- What carat size looks best on a small hand?
- Anything from half a carat upward reads clearly on a slender finger, and an elongated cut flatters it further by lengthening the line of the hand. Size is relative to the finger, which is why a stone that looks modest in a photograph can look substantial in person.
- Is there a big price jump at 1 carat?
- Yes, and it is worth knowing. Prices step sharply at the round numbers because of demand rather than rarity, so a 0.9 carat stone is often materially cheaper than a 1.0 and around 3% smaller in diameter, which nobody can see.
- How do I know the millimetre size of my own stone?
- Measure across the widest point of the stone with a gauge or a ruler, or read it off the certificate, which states the dimensions. That measurement is more useful than the carat weight when you are picturing how it will look.