Diamond Size Chart
Carat weight to millimetres for ten shapes. Drag the slider, pick a shape, and see the stone drawn to scale next to a one-carat round.
Updated
- Face-up size
- 6.4 mm
- Face-up area vs 1 ct round
- 100%
- Weight
- 0.20 g
Drawn in CSS millimetres — close to true size on most screens, not exact. Figures assume typical proportions; a lab report lists a stone’s real measurements.
Diamond size chart: carat to millimetres
Typical face-up dimensions (length × width) for well-proportioned stones. Rounds use the standard trade estimate at about 61.5% depth; fancy shapes scale a typical one-carat outline by the cube root of the weight.
| Carat | Round | Oval | Princess | Cushion | Emerald | Radiant | Asscher | Pear | Marquise | Heart |
|---|---|---|---|---|---|---|---|---|---|---|
| 0.25 ct | 4.1 mm | 4.9 × 3.6 mm | 3.5 × 3.5 mm | 3.5 × 3.5 mm | 4.2 × 3.0 mm | 3.8 × 3.1 mm | 3.5 × 3.5 mm | 5.5 × 3.5 mm | 6.6 × 3.3 mm | 4.1 × 4.1 mm |
| 0.50 ct | 5.1 mm | 6.1 × 4.5 mm | 4.4 × 4.4 mm | 4.4 × 4.4 mm | 5.2 × 3.8 mm | 4.8 × 4.0 mm | 4.4 × 4.4 mm | 6.9 × 4.4 mm | 8.3 × 4.2 mm | 5.2 × 5.2 mm |
| 0.75 ct | 5.8 mm | 7.0 × 5.2 mm | 5.0 × 5.0 mm | 5.0 × 5.0 mm | 6.0 × 4.4 mm | 5.5 × 4.5 mm | 5.0 × 5.0 mm | 7.9 × 5.0 mm | 9.5 × 4.8 mm | 5.9 × 5.9 mm |
| 1.00 ct | 6.4 mm | 7.7 × 5.7 mm | 5.5 × 5.5 mm | 5.5 × 5.5 mm | 6.6 × 4.8 mm | 6.0 × 5.0 mm | 5.5 × 5.5 mm | 8.7 × 5.5 mm | 10.5 × 5.3 mm | 6.5 × 6.5 mm |
| 1.25 ct | 6.9 mm | 8.3 × 6.1 mm | 5.9 × 5.9 mm | 5.9 × 5.9 mm | 7.1 × 5.2 mm | 6.5 × 5.4 mm | 5.9 × 5.9 mm | 9.4 × 5.9 mm | 11.3 × 5.7 mm | 7.0 × 7.0 mm |
| 1.50 ct | 7.4 mm | 8.8 × 6.5 mm | 6.3 × 6.3 mm | 6.3 × 6.3 mm | 7.6 × 5.5 mm | 6.9 × 5.7 mm | 6.3 × 6.3 mm | 10.0 × 6.3 mm | 12.0 × 6.1 mm | 7.4 × 7.4 mm |
| 2.00 ct | 8.1 mm | 9.7 × 7.2 mm | 6.9 × 6.9 mm | 6.9 × 6.9 mm | 8.3 × 6.0 mm | 7.6 × 6.3 mm | 6.9 × 6.9 mm | 11.0 × 6.9 mm | 13.2 × 6.7 mm | 8.2 × 8.2 mm |
| 2.50 ct | 8.7 mm | 10.5 × 7.7 mm | 7.5 × 7.5 mm | 7.5 × 7.5 mm | 9.0 × 6.5 mm | 8.1 × 6.8 mm | 7.5 × 7.5 mm | 11.8 × 7.5 mm | 14.3 × 7.2 mm | 8.8 × 8.8 mm |
| 3.00 ct | 9.3 mm | 11.1 × 8.2 mm | 7.9 × 7.9 mm | 7.9 × 7.9 mm | 9.5 × 6.9 mm | 8.7 × 7.2 mm | 7.9 × 7.9 mm | 12.5 × 7.9 mm | 15.1 × 7.6 mm | 9.4 × 9.4 mm |
| 4.00 ct | 10.2 mm | 12.2 × 9.0 mm | 8.7 × 8.7 mm | 8.7 × 8.7 mm | 10.5 × 7.6 mm | 9.5 × 7.9 mm | 8.7 × 8.7 mm | 13.8 × 8.7 mm | 16.7 × 8.4 mm | 10.3 × 10.3 mm |
| 5.00 ct | 11.0 mm | 13.2 × 9.7 mm | 9.4 × 9.4 mm | 9.4 × 9.4 mm | 11.3 × 8.2 mm | 10.3 × 8.5 mm | 9.4 × 9.4 mm | 14.9 × 9.4 mm | 18.0 × 9.1 mm | 11.1 × 11.1 mm |
How to use the chart
- Compare shapes at the same weight. A 1 ct marquise is over 10 mm long; a 1 ct princess is 5.5 mm square. The price per carat is usually lower for fancy shapes, too.
- Look just under the round numbers. Price per carat steps up at 0.50, 0.70, 0.90, 1.00, 1.50 and 2.00 ct. A 0.90 ct round is only about 0.2 mm narrower than a 1.00 ct.
- Check the certificate’s measurements. Two 1.00 ct rounds can differ by several tenths of a millimetre if one is cut deep.
- Mind total carat weight. A “1 ct TW” cluster ring spreads that weight across many small stones and looks nothing like a 1 ct solitaire.
The reasoning behind the numbers is in Diamond carat vs size; to see how size and shape move the price of a finished ring, try the Engagement Ring Designer. Everything else about grading lives in the Diamond Guide.
Frequently asked questions
How many mm is a 1 carat diamond?
A well-cut 1 carat round brilliant is about 6.4 mm in diameter. A 1 carat oval is roughly 7.7 × 5.7 mm, a princess about 5.5 × 5.5 mm and a marquise about 10.5 × 5.3 mm.
How big is a 2 carat diamond?
A 2 carat round is about 8.1 mm across — only around 26% wider than a 1 carat round, because weight grows with volume rather than with width.
Which diamond shape looks biggest per carat?
Marquise, pear and oval shapes spread their weight across a longer outline and have the most face-up area per carat. Princess, cushion and Asscher shapes look smallest for their weight.
Is the preview on this page actual size?
It is drawn in CSS millimetres, which most phones and monitors render close to real size but not exactly. Use the millimetre figures, not the drawing, for decisions.
Why is my diamond a different size from the chart?
Depth and proportions change how much weight sits below the girdle. A deep stone looks smaller than the chart, and a shallow one looks larger but may leak light. The lab report lists the stone’s real measurements.
Sources and further reading
- The 4Cs of Diamond Quality — GIA (Gemological Institute of America)
- Diamond Description — GIA
- Diamond cut — Wikipedia
Links checked September 14, 2026.