Diamond Size Chart: Carat to MM by Shape
How big is a 1 carat diamond? A 1 carat round diamond measures about 6.4 mm across, a 2 carat round about 8 mm and a 3 carat round about 9.1 mm. The chart below gives the typical face-up size in millimeters for ten diamond shapes from 0.50 to 3.00 carats, so you can compare a 1 carat oval (about 8 x 5.5 mm) with a 1 carat pear (about 8.5 x 5.5 mm) before you choose.
Diamond size chart: carat to mm by shape
Sizes are length x width in millimeters, as seen from the top. Every diamond is cut a little differently, so a real stone can measure slightly more or less than the chart.
| Shape | 0.50 ct | 0.75 ct | 1.00 ct | 1.25 ct | 1.50 ct | 2.00 ct | 2.50 ct | 3.00 ct |
|---|---|---|---|---|---|---|---|---|
| Round | 5 mm | 5.75 mm | 6.4 mm | 6.8 mm | 7.3 mm | 8 mm | 8.6 mm | 9.1 mm |
| Oval | 6 x 4 mm | 7.5 x 5 mm | 8 x 5.5 mm | 8.5 x 5.5 mm | 9 x 6 mm | 10.5 x 7 mm | 11 x 7.5 mm | 11.5 x 7.5 mm |
| Pear | 7 x 4.5 mm | 8 x 5 mm | 8.5 x 5.5 mm | 9.5 x 6 mm | 10 x 6.5 mm | 10.5 x 7 mm | 11.5 x 7.5 mm | 12.5 x 8 mm |
| Princess | 4.4 mm | 5 mm | 5.5 mm | 5.9 mm | 6.4 mm | 7 mm | 7.5 mm | 8 mm |
| Cushion | 5 x 4.5 mm | 6 x 5 mm | 6.5 x 5.5 mm | 7 x 6 mm | 7.5 x 6.5 mm | 8 x 7 mm | 8.5 x 7.5 mm | 9 x 8 mm |
| Emerald | 5.5 x 4 mm | 6 x 4.5 mm | 6.5 x 5 mm | 7 x 5.5 mm | 7.5 x 5.5 mm | 8.5 x 6 mm | 9 x 6.5 mm | 9.5 x 7 mm |
| Asscher | 4.4 mm | 5 mm | 5.5 mm | 6 mm | 6.4 mm | 7 mm | 7.5 mm | 8.1 mm |
| Radiant | 5 x 4.5 mm | 5.5 x 5 mm | 6 x 5.5 mm | 6.5 x 5.8 mm | 7 x 6 mm | 7.5 x 7 mm | 8 x 7.2 mm | 8.5 x 7.5 mm |
| Marquise | 8.5 x 4 mm | 9.5 x 4.5 mm | 10.5 x 5 mm | 11.5 x 5.5 mm | 12 x 6 mm | 13 x 6.5 mm | 13.5 x 6.8 mm | 14 x 7 mm |
| Heart | 5.4 mm | 6 mm | 6.7 mm | 7.1 mm | 7.6 mm | 8.3 mm | 9 mm | 9.5 mm |
How to use a diamond size chart
Carat is a weight, not a size. Two diamonds of the same weight can look different on the hand, because the cut decides how much of that weight sits in the visible top and how much is hidden below. Elongated shapes such as oval, pear and marquise spread their weight over a longer outline, so they look larger than a round of the same carat. For a full explanation of carat, cut, color and clarity, see our diamond education guide.
Black diamonds are often cut deeper than white ones, so with a black diamond, ask for its size in millimeters as well as its weight. Every product page on our site lists the center stone's carat weight; our team can give you the measurements of any stone. See our black diamond engagement rings and natural diamond engagement rings.
Diamond size chart: FAQ
How many mm is a 1 carat diamond?
About 6.4 mm across for a round. A 1 carat oval is about 8 x 5.5 mm, a pear about 8.5 x 5.5 mm, a princess about 5.5 mm and an emerald cut about 6.5 x 5 mm.
What size is a pear shaped diamond by carat?
About 7 x 4.5 mm at 0.50 carat, 8.5 x 5.5 mm at 1 carat, 10.5 x 7 mm at 2 carats and 12.5 x 8 mm at 3 carats. See our pear diamond engagement rings.
Does a 2 carat diamond look twice as big as a 1 carat?
No. Weight grows in three dimensions, but you only see the top. A 2 carat round is about 8 mm across against 6.4 mm for a 1 carat, which is about 25% wider, not twice as wide.
Which diamond shape looks biggest for its carat weight?
Elongated shapes. In the chart, a 1 carat marquise is about 10.5 mm long and a 1 carat oval about 8 mm, against 6.4 mm for a 1 carat round.
Can I see my ring size too?
Yes. See our ring size chart and how to find a ring size. For any other question, contact us.