Diamond carat size chart: 0.1 to 100 carat in mm

By HeyGema™ · Updated November 5, 2026

In short

A round diamond grows with the cube root of its weight: 1 carat is 6.5 mm, 2 carat 8.1 mm and 5 carat 11.0 mm. Pick a weight for its chart in every shape.

Carat to mm calculator

ShapeGemCarat

About 6.5 x 6.5 mm

An estimate for a well-cut stone. A deep or shallow cut faces up smaller or bigger.

Round diamond size by carat weight

Face-up diameter of a well-cut round diamond. Every weight links to its own page with oval, cushion, emerald cut and nine more shapes.

0.1 carat: Diameter: 2.99 mm; Inches: 0.12 in; Weight: 0.020 g

0.15 carat: Diameter: 3.4 mm; Inches: 0.13 in; Weight: 0.030 g

0.2 carat: Diameter: 3.8 mm; Inches: 0.15 in; Weight: 0.040 g

0.25 carat: Diameter: 4.1 mm; Inches: 0.16 in; Weight: 0.050 g

0.3 carat: Diameter: 4.3 mm; Inches: 0.17 in; Weight: 0.060 g

0.33 carat: Diameter: 4.5 mm; Inches: 0.18 in; Weight: 0.066 g

0.4 carat: Diameter: 4.8 mm; Inches: 0.19 in; Weight: 0.080 g

0.5 carat: Diameter: 5.1 mm; Inches: 0.20 in; Weight: 0.10 g

0.6 carat: Diameter: 5.4 mm; Inches: 0.21 in; Weight: 0.12 g

0.7 carat: Diameter: 5.7 mm; Inches: 0.23 in; Weight: 0.14 g

0.75 carat: Diameter: 5.9 mm; Inches: 0.23 in; Weight: 0.15 g

0.8 carat: Diameter: 6.0 mm; Inches: 0.24 in; Weight: 0.16 g

0.9 carat: Diameter: 6.2 mm; Inches: 0.25 in; Weight: 0.18 g

1 carat: Diameter: 6.5 mm; Inches: 0.25 in; Weight: 0.20 g

1.1 carat: Diameter: 6.7 mm; Inches: 0.26 in; Weight: 0.22 g

1.2 carat: Diameter: 6.9 mm; Inches: 0.27 in; Weight: 0.24 g

1.25 carat: Diameter: 6.9 mm; Inches: 0.27 in; Weight: 0.25 g

1.3 carat: Diameter: 7.0 mm; Inches: 0.28 in; Weight: 0.26 g

1.4 carat: Diameter: 7.2 mm; Inches: 0.28 in; Weight: 0.28 g

1.5 carat: Diameter: 7.4 mm; Inches: 0.29 in; Weight: 0.30 g

1.6 carat: Diameter: 7.5 mm; Inches: 0.30 in; Weight: 0.32 g

1.7 carat: Diameter: 7.7 mm; Inches: 0.30 in; Weight: 0.34 g

1.75 carat: Diameter: 7.8 mm; Inches: 0.31 in; Weight: 0.35 g

1.8 carat: Diameter: 7.8 mm; Inches: 0.31 in; Weight: 0.36 g

1.9 carat: Diameter: 8.0 mm; Inches: 0.31 in; Weight: 0.38 g

2 carat: Diameter: 8.1 mm; Inches: 0.32 in; Weight: 0.40 g

2.1 carat: Diameter: 8.3 mm; Inches: 0.33 in; Weight: 0.42 g

2.2 carat: Diameter: 8.4 mm; Inches: 0.33 in; Weight: 0.44 g

2.25 carat: Diameter: 8.5 mm; Inches: 0.33 in; Weight: 0.45 g

2.3 carat: Diameter: 8.5 mm; Inches: 0.34 in; Weight: 0.46 g

2.4 carat: Diameter: 8.6 mm; Inches: 0.34 in; Weight: 0.48 g

2.5 carat: Diameter: 8.8 mm; Inches: 0.34 in; Weight: 0.50 g

2.6 carat: Diameter: 8.9 mm; Inches: 0.35 in; Weight: 0.52 g

2.7 carat: Diameter: 9.0 mm; Inches: 0.35 in; Weight: 0.54 g

2.75 carat: Diameter: 9.0 mm; Inches: 0.36 in; Weight: 0.55 g

2.8 carat: Diameter: 9.1 mm; Inches: 0.36 in; Weight: 0.56 g

2.9 carat: Diameter: 9.2 mm; Inches: 0.36 in; Weight: 0.58 g

3 carat: Diameter: 9.3 mm; Inches: 0.37 in; Weight: 0.60 g

3.25 carat: Diameter: 9.6 mm; Inches: 0.38 in; Weight: 0.65 g

3.5 carat: Diameter: 9.8 mm; Inches: 0.39 in; Weight: 0.70 g

3.75 carat: Diameter: 10.0 mm; Inches: 0.39 in; Weight: 0.75 g

4 carat: Diameter: 10.2 mm; Inches: 0.40 in; Weight: 0.80 g

4.5 carat: Diameter: 10.6 mm; Inches: 0.42 in; Weight: 0.90 g

5 carat: Diameter: 11.0 mm; Inches: 0.43 in; Weight: 1.00 g

6 carat: Diameter: 11.7 mm; Inches: 0.46 in; Weight: 1.20 g

7 carat: Diameter: 12.3 mm; Inches: 0.49 in; Weight: 1.40 g

8 carat: Diameter: 12.9 mm; Inches: 0.51 in; Weight: 1.60 g

9 carat: Diameter: 13.4 mm; Inches: 0.53 in; Weight: 1.80 g

10 carat: Diameter: 13.9 mm; Inches: 0.55 in; Weight: 2.00 g

12 carat: Diameter: 14.8 mm; Inches: 0.58 in; Weight: 2.40 g

15 carat: Diameter: 15.9 mm; Inches: 0.63 in; Weight: 3.00 g

20 carat: Diameter: 17.5 mm; Inches: 0.69 in; Weight: 4.00 g

25 carat: Diameter: 18.9 mm; Inches: 0.74 in; Weight: 5.00 g

30 carat: Diameter: 20.0 mm; Inches: 0.79 in; Weight: 6.00 g

40 carat: Diameter: 22.1 mm; Inches: 0.87 in; Weight: 8.00 g

50 carat: Diameter: 23.8 mm; Inches: 0.94 in; Weight: 10.00 g

75 carat: Diameter: 27.2 mm; Inches: 1.07 in; Weight: 15.00 g

100 carat: Diameter: 29.9 mm; Inches: 1.18 in; Weight: 20.00 g

Carat	Diameter	Inches	Weight
0.1 carat	2.99 mm	0.12 in	0.020 g
0.15 carat	3.4 mm	0.13 in	0.030 g
0.2 carat	3.8 mm	0.15 in	0.040 g
0.25 carat	4.1 mm	0.16 in	0.050 g
0.3 carat	4.3 mm	0.17 in	0.060 g
0.33 carat	4.5 mm	0.18 in	0.066 g
0.4 carat	4.8 mm	0.19 in	0.080 g
0.5 carat	5.1 mm	0.20 in	0.10 g
0.6 carat	5.4 mm	0.21 in	0.12 g
0.7 carat	5.7 mm	0.23 in	0.14 g
0.75 carat	5.9 mm	0.23 in	0.15 g
0.8 carat	6.0 mm	0.24 in	0.16 g
0.9 carat	6.2 mm	0.25 in	0.18 g
1 carat	6.5 mm	0.25 in	0.20 g
1.1 carat	6.7 mm	0.26 in	0.22 g
1.2 carat	6.9 mm	0.27 in	0.24 g
1.25 carat	6.9 mm	0.27 in	0.25 g
1.3 carat	7.0 mm	0.28 in	0.26 g
1.4 carat	7.2 mm	0.28 in	0.28 g
1.5 carat	7.4 mm	0.29 in	0.30 g
1.6 carat	7.5 mm	0.30 in	0.32 g
1.7 carat	7.7 mm	0.30 in	0.34 g
1.75 carat	7.8 mm	0.31 in	0.35 g
1.8 carat	7.8 mm	0.31 in	0.36 g
1.9 carat	8.0 mm	0.31 in	0.38 g
2 carat	8.1 mm	0.32 in	0.40 g
2.1 carat	8.3 mm	0.33 in	0.42 g
2.2 carat	8.4 mm	0.33 in	0.44 g
2.25 carat	8.5 mm	0.33 in	0.45 g
2.3 carat	8.5 mm	0.34 in	0.46 g
2.4 carat	8.6 mm	0.34 in	0.48 g
2.5 carat	8.8 mm	0.34 in	0.50 g
2.6 carat	8.9 mm	0.35 in	0.52 g
2.7 carat	9.0 mm	0.35 in	0.54 g
2.75 carat	9.0 mm	0.36 in	0.55 g
2.8 carat	9.1 mm	0.36 in	0.56 g
2.9 carat	9.2 mm	0.36 in	0.58 g
3 carat	9.3 mm	0.37 in	0.60 g
3.25 carat	9.6 mm	0.38 in	0.65 g
3.5 carat	9.8 mm	0.39 in	0.70 g
3.75 carat	10.0 mm	0.39 in	0.75 g
4 carat	10.2 mm	0.40 in	0.80 g
4.5 carat	10.6 mm	0.42 in	0.90 g
5 carat	11.0 mm	0.43 in	1.00 g
6 carat	11.7 mm	0.46 in	1.20 g
7 carat	12.3 mm	0.49 in	1.40 g
8 carat	12.9 mm	0.51 in	1.60 g
9 carat	13.4 mm	0.53 in	1.80 g
10 carat	13.9 mm	0.55 in	2.00 g
12 carat	14.8 mm	0.58 in	2.40 g
15 carat	15.9 mm	0.63 in	3.00 g
20 carat	17.5 mm	0.69 in	4.00 g
25 carat	18.9 mm	0.74 in	5.00 g
30 carat	20.0 mm	0.79 in	6.00 g
40 carat	22.1 mm	0.87 in	8.00 g
50 carat	23.8 mm	0.94 in	10.00 g
75 carat	27.2 mm	1.07 in	15.00 g
100 carat	29.9 mm	1.18 in	20.00 g

Why double the weight is not double the size

Weight grows with volume, and every side of the stone grows with the cube root of the weight. A 2 carat round is 26% wider than a 1 carat, not twice as wide. Its face-up area is 59% bigger.

Questions

Carat is weight and mm is size, so the answer depends on the shape. For a round diamond the diameter in mm is about 6.45 times the cube root of the carat weight. The table above and the calculator do this for every shape.

A 6.5 mm round diamond weighs about 1 carat. See the mm to carat pages.