Diamond Carat Size Chart: Real Millimeter Sizes by Shape
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A carat is a unit of weight, not size: one carat is 0.2 grams. Measured across the top, a typical 1 carat round lab grown diamond is about 6.5 mm, a 2 carat about 8.1 mm and a 3 carat about 9.3 mm. Oval, pear and marquise diamonds of the same weight are longer, so they often look bigger.
Most carat size charts online use ideal numbers. This chart uses real measurements: the middle size of the white lab grown diamonds in our own diamond list, by shape and carat weight, checked on 6 October 2026.
Round diamond sizes, drawn to scale
The diamonds are drawn to the same scale, so you can compare them with each other. The size you see on your screen depends on your device.
| Carat weight | Typical diameter | Share of a size 6 finger |
|---|---|---|
| 0.5 carat | 5.1 mm | 31% |
| 0.75 carat | 5.8 mm | 35% |
| 1 carat | 6.5 mm | 39% |
| 1.5 carats | 7.4 mm | 45% |
| 2 carats | 8.1 mm | 49% |
| 2.5 carats | 8.7 mm | 53% |
| 3 carats | 9.3 mm | 56% |
| 4 carats | 10.2 mm | 62% |
Median diameter of white round lab grown diamonds in the Milagros diamond list. "Share of a size 6 finger" compares the diamond with the inside of a US size 6 ring, about 16.5 mm across.
Twice the carats is not twice the size
Going from 1 carat to 2 carats makes a round diamond about 25% wider (6.5 mm to 8.1 mm). Its top surface grows by about 56%. A 3 carat round has about twice the top surface of a 1 carat. This is because much of the extra weight goes into the depth of the stone, where you cannot see it.
Carat size chart for every shape
For long shapes, the first number is the length and the second is the width.
| Carat | Round | Oval | Emerald | Pear |
|---|---|---|---|---|
| 0.5 ct | 5.1 mm | 6.5 × 4.4 | 5.6 × 3.8 | 7.3 × 4.4 |
| 0.75 ct | 5.8 mm | 7.5 × 5.1 | 6.3 × 4.3 | 8.2 × 5.0 |
| 1 ct | 6.5 mm | 8.0 × 5.7 | 6.8 × 4.7 | 8.8 × 5.6 |
| 1.5 ct | 7.4 mm | 9.2 × 6.4 | 7.7 × 5.4 | 9.9 × 6.4 |
| 2 ct | 8.1 mm | 10.2 × 7.1 | 8.6 × 5.9 | 11.1 × 7.0 |
| 2.5 ct | 8.7 mm | 11.0 × 7.6 | 9.3 × 6.4 | 12.1 × 7.5 |
| 3 ct | 9.3 mm | 11.7 × 8.1 | 9.9 × 6.7 | 12.5 × 8.1 |
| 4 ct | 10.2 mm | 12.8 × 8.9 | 11.0 × 7.3 | 13.7 × 8.8 |
| Carat | Radiant | Princess | Marquise |
|---|---|---|---|
| 0.5 ct | 5.7 × 4.0 | 4.4 × 4.3 | 8.3 × 4.1 |
| 0.75 ct | 6.5 × 4.5 | 4.9 × 4.9 | 9.6 × 4.8 |
| 1 ct | 7.1 × 5.0 | 5.5 × 5.4 | 10.6 × 5.2 |
| 1.5 ct | 8.1 × 5.6 | 6.3 × 6.2 | 11.8 × 6.0 |
| 2 ct | 8.8 × 6.2 | 6.9 × 6.8 | 12.9 × 6.6 |
| 2.5 ct | 9.9 × 6.6 | 7.4 × 7.4 | 14.0 × 7.0 |
| 3 ct | 10.1 × 7.1 | 7.8 × 7.8 | 15.2 × 7.4 |
| 4 ct | 11.4 × 7.7 | 8.7 × 8.6 | 16.4 × 8.3 |
All sizes in millimeters. Median measurements of white lab grown diamonds in the Milagros diamond list on 6 October 2026, for diamonds within a few hundredths of each carat weight. Cushion cuts are not shown because square and long cushions are mixed together in our list.
Why two diamonds of the same weight can look different
- ShapeLong shapes spread their weight over a bigger outline. A 1 carat marquise is 10.6 mm long; a 1 carat princess is 5.5 mm across.
- DepthA diamond cut deeper keeps more weight underneath, so it looks a little smaller from the top. Check the measurements on the IGI report, not only the carats.
- SettingA halo of small diamonds makes the center look bigger. A thin band also makes the center stone look larger.
- Your handThe same diamond looks bigger on a smaller finger. Check your size with our ring size guide.
How to choose your carat size
- Start with your budget. See what each carat weight costs in our lab grown diamond price guide.
- Pick the shape. If you want the most size for the weight, look at oval, pear and marquise. Read our oval diamond guide and emerald cut guide.
- Check the millimeters. Compare the measurements on the IGI report with the chart above.
- See it on a hand. Book an appointment in New York or on a video call, and we will show you different sizes side by side.
Questions
How big is a 1 carat diamond in mm?
A typical 1 carat round lab grown diamond in our list is about 6.5 mm across. A 1 carat oval is about 8.0 × 5.7 mm.
How big is a 2 carat diamond?
A typical 2 carat round is about 8.1 mm across. A 2 carat oval is about 10.2 × 7.1 mm and a 2 carat emerald cut about 8.6 × 5.9 mm.
Is a lab grown diamond the same size as a natural diamond of the same carat?
Yes. Lab grown and natural diamonds are the same material, so the same weight and cut give the same size.
Which shape looks biggest for its carat weight?
In our list, marquise, pear and oval diamonds have the longest outline for their weight. A 1 carat marquise is about 10.6 mm long.
Find your size
Every center diamond comes with its own IGI report, with its exact measurements.
Book an appointment- Milagros Jewel data: measurements of white lab grown diamonds in our diamond list, sampled across the full price range for each shape and carat weight, checked on 6 October 2026. Middle (median) values are shown.
- US ring size 6 has an inside diameter of 16.5 mm, from our ring size guide.
