How big is 1 carat on the finger? The size chart

Carat tells you the weight of a diamond, but on your finger you do not see grams, you see an area. That is why the question "how big does 1 carat actually look" often matters more than the number on the certificate. The answer depends mostly on the cut, but for the most popular cut, the round brilliant, there are reliable diameter figures, which we show you here.

The carat size chart

The following values apply to a round brilliant cut with common proportions. They are guide figures, because two diamonds of the same weight can look slightly different in size depending on cut quality, but as an orientation they are very reliable.

• 0.3 carat, diameter about 4.3 mm
• 0.5 carat, diameter about 5.1 mm
• 0.7 carat, diameter about 5.7 mm
• 1 carat, diameter about 6.4 mm
• 1.5 carat, diameter about 7.4 mm
• 2 carat, diameter about 8.1 mm
• 3 carat, diameter about 9.3 mm

What stands out here: the weight doubles from 1 to 2 carat, but the diameter only grows by about a quarter, from 6.4 to 8.1 mm. That is because carat measures volume, while what you see from above is only the surface area, and area grows much more slowly than volume. A jump from 1 to 1.5 carat therefore often looks more striking on the finger than the raw numbers suggest, while the jump from 2 to 3 carat looks visually smaller than the weight increase implies.

Why the cut changes how it looks

The chart applies to the round brilliant, by far the most common cut. Other shapes look bigger or smaller at the same weight. An oval or a marquise cut, for example, stretches the surface lengthways and often looks bigger than a round stone of the same carat, because more weight goes into the surface instead of the depth. A princess or cushion cut with more angular shapes can also show a bigger surface per carat. So if size on the finger matters more to you than a specific shape, it is worth looking beyond the round brilliant. We explain how the different cuts differ in detail, and which suits which hand shape, in our article on finding your diamond shape.

The setting also affects how big a stone looks. A bezel setting that exposes the stone makes it look bigger than a deep prong setting that hides part of it. A halo of small diamonds around the centre stone adds to the visual size further, without the main stone itself getting any bigger.

Carat is only one of four factors

As useful as the size chart is, carat alone says nothing about how a diamond sparkles or how valuable it is. Colour, clarity and cut quality, known together as the four C's, influence how a stone looks and what it costs at least as strongly. A smaller stone with a very good cut can sparkle brighter than a larger one with a mediocre cut. We explain the four C's without the jargon in our basics article on the 4C's, so you know what matters beyond raw size during the consultation.

At émin, we always show you several stones of different sizes right on your finger in the atelier, under daylight and under room light, so you see how 0.7, 1 or 1.5 carat actually feels on your own hand, instead of relying on a chart. You will find more on lab-grown diamonds in various sizes on our lab-grown diamonds page.

In the end, what counts is not the number on paper, but how the ring looks and feels on your hand, every day. That is exactly what we take time for at an appointment in our atelier in Zurich district 4 or by video, with real stones to look at, not just a chart.