Free Diamond Size Chart & Comparison
A diamond size chart shows the face-up millimeter dimensions of a diamond at each carat weight, by shape. A well-cut 1 carat round diamond is about 6.5 mm across, and a 2 carat round is about 8.2 mm.
Use this diamond carat size chart to convert carat to mm, compare shapes side by side to scale, see the diamond size on your finger, and estimate carat weight from a measurement. Sizes are typical for well-cut stones and vary with depth and proportions.
1 ct Round brilliant
6.5 mm
33.2 mm² face-up
Diamond carat size chart by shape
Pick a shape to see its diamond mm size chart, then pick a carat weight to highlight it.
Measured across the diameter. The benchmark most charts start from.
| Carat | Diameter | Face-up area |
|---|---|---|
| 0.25 ct | 4.1 mm | 13.2 mm² |
| 0.33 ct | 4.4 mm | 15.2 mm² |
| 0.5 ct | 5.2 mm | 21.2 mm² |
| 0.75 ct | 5.8 mm | 26.4 mm² |
| 0.9 ct | 6.2 mm | 30.2 mm² |
| 1 ct | 6.5 mm | 33.2 mm² |
| 1.25 ct | 6.9 mm | 37.4 mm² |
| 1.5 ct | 7.4 mm | 43.0 mm² |
| 1.75 ct | 7.8 mm | 47.8 mm² |
| 2 ct | 8.2 mm | 52.8 mm² |
| 2.5 ct | 8.8 mm | 60.8 mm² |
| 3 ct | 9.4 mm | 69.4 mm² |
| 4 ct | 10.2 mm | 81.7 mm² |
| 5 ct | 11.1 mm | 96.8 mm² |
Round brilliant sizes side by side, to scale
- 0.25
- 0.33
- 0.5
- 0.75
- 0.9
- 1
- 1.25
- 1.5
- 1.75
- 2
- 2.5
- 3
- 4
- 5
Numbers under each outline are carats. Drawn at 2x actual size, using the scale set in the calibration section below.
Diamond size comparison
Compare two or three shape and carat combinations to scale. Differences are in face-up area against the first stone. Drawn at 2x actual size.
- A 1 ct oval looks about 4% larger face-up than a 1 ct round.
Diamond size on finger
Shows the 1 ct round brilliant selected in the chart on a band, from above.
- Finger coverage
- 38%
- Stone across the finger
- 6.5 mm of 17.3 mm
Drawn at 2x actual size. Finger width at the band is taken as the ring's inner diameter. Elongated shapes are set north-south, length along the finger.
Diamond mm to carat estimate
Measured a stone? Enter its size to estimate the carat weight with standard trade formulas.
Estimated weight
~1.03 ct
6.5² x 4 x 0.0061 = 1.03 ct
Closest chart size: 1 ct round brilliant (6.5 mm).
This is an estimate, not a weighing. Mounted stones, unusual depth, or a thick girdle can shift the real weight by 10% or more. Only a scale gives the true carat weight.
View diamonds at actual size
Screens differ, so the drawings are only true to size after you calibrate. Hold a bank or ID card (85.6 mm wide) against the screen and move the slider until the outline below matches the card's width. To print at actual size, keep the default scale and print at 100% with no "fit to page".
How to use this diamond size chart
- 1
Choose a shape
Pick from 10 shapes to load its carat to mm chart and outlines.
- 2
Pick a carat
Select 0.25 to 5 ct to see the typical face-up size and area.
- 3
Compare and preview
Compare up to three stones and see the diamond on your ring size.
- 4
Calibrate
Match the card outline to a real bank card so outlines show true size.
Disclaimer: sizes are approximate values for well-cut stones, for planning only. Actual dimensions vary with cut, depth, and table proportions, so two diamonds of the same weight can differ by several tenths of a millimeter. Round sizes follow widely published diameter charts; fancy shapes scale from typical 1 ct dimensions. This is not an appraisal or a grading report.
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Diamond size FAQ
How big is a 1 carat diamond in mm?
A well-cut 1 carat round diamond is about 6.5 mm across. Fancy shapes of the same weight are roughly 7.7 x 5.7 mm for an oval, 5.5 x 5.5 mm for a princess, 7 x 5 mm for an emerald, 8 x 5.5 mm for a pear, and 10 x 5 mm for a marquise.
Which diamond shape looks biggest per carat?
Elongated shapes look biggest. A 1 ct marquise (about 10 x 5 mm) and a 1 ct oval (about 7.7 x 5.7 mm) spread roughly 4 to 5% more face-up area than a 6.5 mm round and look longer on the finger. Pears also look large for their weight. Princess, asscher, and heart cuts face up smaller because more of their weight sits in depth.
How do I measure a diamond in mm?
Use a millimeter gauge or digital caliper. Measure the diameter across the girdle of a round stone, or the length and width of a fancy shape, and the depth from table to culet. A grading report lists these as, for example, 6.45-6.48 x 3.98 mm.
Does a 2 carat diamond look twice as big as a 1 carat?
No. Weight is spread through the stone's depth, so a 2 ct round is about 8.2 mm across versus 6.5 mm for 1 ct. That is about 26% wider and about 59% more face-up area, not double.
How does ring size affect how big a diamond looks?
The same diamond looks bigger on a slimmer finger. A 6.5 mm 1 ct round covers about 41% of the width of a US 5 finger (15.7 mm) but about 34% of a US 9 finger (19 mm). Elongated shapes set north-south also make fingers look slimmer.