Round diamond CAD size table: diameter, depth and carat weight

By HeyGema™ · Updated November 5, 2026

In short

A well-cut round diamond is about 60% as deep as it is wide. A 6.5 mm stone is then 3.90 mm deep and weighs about 1.02 carat. The table gives the diameter, depth and weight to model from.

Round brilliant diameter, depth and weight

Depth is taken as 60% of the diameter, within the usual range of 59% to 62%. Weight is diameter x diameter x depth x 0.0061. Add the girdle to your model; the table treats it as part of the depth.

1 mm: Depth (60%): 0.60 mm; Weight: 0.0037 ct; Stones per carat: 273

1.1 mm: Depth (60%): 0.66 mm; Weight: 0.0049 ct; Stones per carat: 205

1.2 mm: Depth (60%): 0.72 mm; Weight: 0.0063 ct; Stones per carat: 158

1.3 mm: Depth (60%): 0.78 mm; Weight: 0.0080 ct; Stones per carat: 124

1.4 mm: Depth (60%): 0.84 mm; Weight: 0.0100 ct; Stones per carat: 100

1.5 mm: Depth (60%): 0.90 mm; Weight: 0.0124 ct; Stones per carat: 81

1.6 mm: Depth (60%): 0.96 mm; Weight: 0.0150 ct; Stones per carat: 67

1.7 mm: Depth (60%): 1.02 mm; Weight: 0.0180 ct; Stones per carat: 56

1.8 mm: Depth (60%): 1.08 mm; Weight: 0.0213 ct; Stones per carat: 47

1.9 mm: Depth (60%): 1.14 mm; Weight: 0.0251 ct; Stones per carat: 40

2 mm: Depth (60%): 1.20 mm; Weight: 0.0293 ct; Stones per carat: 34

2.1 mm: Depth (60%): 1.26 mm; Weight: 0.0339 ct; Stones per carat: 30

2.2 mm: Depth (60%): 1.32 mm; Weight: 0.0390 ct; Stones per carat: 26

2.3 mm: Depth (60%): 1.38 mm; Weight: 0.0445 ct; Stones per carat: 22

2.4 mm: Depth (60%): 1.44 mm; Weight: 0.0506 ct; Stones per carat: 20

2.5 mm: Depth (60%): 1.50 mm; Weight: 0.0572 ct; Stones per carat: 17

2.6 mm: Depth (60%): 1.56 mm; Weight: 0.0643 ct; Stones per carat: 16

2.7 mm: Depth (60%): 1.62 mm; Weight: 0.0720 ct; Stones per carat: 14

2.8 mm: Depth (60%): 1.68 mm; Weight: 0.0803 ct; Stones per carat: 12

2.9 mm: Depth (60%): 1.74 mm; Weight: 0.0893 ct; Stones per carat: 11

3 mm: Depth (60%): 1.80 mm; Weight: 0.0988 ct; Stones per carat: 10

3.3 mm: Depth (60%): 1.95 mm; Weight: 0.126 ct; Stones per carat: 8

3.5 mm: Depth (60%): 2.10 mm; Weight: 0.157 ct; Stones per carat: 6

3.8 mm: Depth (60%): 2.25 mm; Weight: 0.193 ct; Stones per carat: 5

4 mm: Depth (60%): 2.40 mm; Weight: 0.234 ct; Stones per carat: 4

4.5 mm: Depth (60%): 2.70 mm; Weight: 0.334 ct; Stones per carat: 3

5 mm: Depth (60%): 3.00 mm; Weight: 0.458 ct; Stones per carat: 2

5.5 mm: Depth (60%): 3.30 mm; Weight: 0.609 ct; Stones per carat: 2

6 mm: Depth (60%): 3.60 mm; Weight: 0.791 ct; Stones per carat: 1

6.5 mm: Depth (60%): 3.90 mm; Weight: 1.005 ct; Stones per carat: -

7 mm: Depth (60%): 4.20 mm; Weight: 1.255 ct; Stones per carat: -

7.5 mm: Depth (60%): 4.50 mm; Weight: 1.544 ct; Stones per carat: -

8 mm: Depth (60%): 4.80 mm; Weight: 1.874 ct; Stones per carat: -

9 mm: Depth (60%): 5.40 mm; Weight: 2.668 ct; Stones per carat: -

10 mm: Depth (60%): 6.00 mm; Weight: 3.660 ct; Stones per carat: -

11 mm: Depth (60%): 6.60 mm; Weight: 4.871 ct; Stones per carat: -

12 mm: Depth (60%): 7.20 mm; Weight: 6.324 ct; Stones per carat: -

Diameter	Depth (60%)	Weight	Stones per carat
1 mm	0.60 mm	0.0037 ct	273
1.1 mm	0.66 mm	0.0049 ct	205
1.2 mm	0.72 mm	0.0063 ct	158
1.3 mm	0.78 mm	0.0080 ct	124
1.4 mm	0.84 mm	0.0100 ct	100
1.5 mm	0.90 mm	0.0124 ct	81
1.6 mm	0.96 mm	0.0150 ct	67
1.7 mm	1.02 mm	0.0180 ct	56
1.8 mm	1.08 mm	0.0213 ct	47
1.9 mm	1.14 mm	0.0251 ct	40
2 mm	1.20 mm	0.0293 ct	34
2.1 mm	1.26 mm	0.0339 ct	30
2.2 mm	1.32 mm	0.0390 ct	26
2.3 mm	1.38 mm	0.0445 ct	22
2.4 mm	1.44 mm	0.0506 ct	20
2.5 mm	1.50 mm	0.0572 ct	17
2.6 mm	1.56 mm	0.0643 ct	16
2.7 mm	1.62 mm	0.0720 ct	14
2.8 mm	1.68 mm	0.0803 ct	12
2.9 mm	1.74 mm	0.0893 ct	11
3 mm	1.80 mm	0.0988 ct	10
3.3 mm	1.95 mm	0.126 ct	8
3.5 mm	2.10 mm	0.157 ct	6
3.8 mm	2.25 mm	0.193 ct	5
4 mm	2.40 mm	0.234 ct	4
4.5 mm	2.70 mm	0.334 ct	3
5 mm	3.00 mm	0.458 ct	2
5.5 mm	3.30 mm	0.609 ct	2
6 mm	3.60 mm	0.791 ct	1
6.5 mm	3.90 mm	1.005 ct	-
7 mm	4.20 mm	1.255 ct	-
7.5 mm	4.50 mm	1.544 ct	-
8 mm	4.80 mm	1.874 ct	-
9 mm	5.40 mm	2.668 ct	-
10 mm	6.00 mm	3.660 ct	-
11 mm	6.60 mm	4.871 ct	-
12 mm	7.20 mm	6.324 ct	-

Tolkowsky's proportions

The classic ideal round brilliant of 1919 (Marcel Tolkowsky) is a good starting model. Crown height = (100 - table %) / 2 x tan(crown angle); pavilion depth = 50 x tan(pavilion angle), both as a percent of the diameter.

Table: Tolkowsky (1919): 53%

Crown angle: Tolkowsky (1919): 34.5 degrees

Crown height: Tolkowsky (1919): 16.2%

Pavilion angle: Tolkowsky (1919): 40.75 degrees

Pavilion depth: Tolkowsky (1919): 43.1%

Total depth: Tolkowsky (1919): 59.3%

Part	Tolkowsky (1919)
Table	53%
Crown angle	34.5 degrees
Crown height	16.2%
Pavilion angle	40.75 degrees
Pavilion depth	43.1%
Total depth	59.3%

Modern ideal ranges differ slightly by lab, and real cutters add a girdle of 1% to 3%. Use the numbers as a modeling default, and read an actual stone's proportions from its report.

From CAD to render

Size the stones in your CAD model, then render the piece to show it to the client. HeyGema renders a Rhino, STEP, OBJ or GLB file into a photorealistic image of the finished piece. See HeyGema for Rhino and the render tool.

Questions

About 3.90 mm, using 60% of the diameter. Real stones range from about 59% to 62.5%.

About 0.0124 carat, so 81 stones make a carat. Small melee is often cut thicker and weighs more per stone.

A table of 53% to 58%, a crown angle of 34 to 35 degrees and a pavilion angle of 40.6 to 41 degrees is a common ideal range. Tolkowsky's 1919 values are the classic reference.