Calibrated gemstone sizes chart: standard stone sizes in mm and carats

By HeyGema™ · Updated November 5, 2026

In short

Settings are made for standard stone sizes. A 6.5 mm round is about 1.02 carat in diamond, an 8 x 6 mm oval about 1.14 carat and a 7 x 5 mm emerald cut about 1 carat. Weights are estimates for a well-cut stone.

What calibrated sizes are

Ready-made settings, mountings and findings are made for standard stone sizes in mm, called calibrated sizes. A stone cut to one of them drops into a standard head without custom work. The weights below are our estimate for a well-cut diamond of that size; a real stone cut to a calibrated size can be shallower or deeper, and so lighter or heavier.

Round calibrated sizes

1 mm: Diamond weight: 0.0000 ct; Moissanite (true weight): 0.0000 ct; Sapphire: 0.0000 ct

1.5 mm: Diamond weight: 0.010 ct; Moissanite (true weight): 0.010 ct; Sapphire: 0.010 ct

2 mm: Diamond weight: 0.030 ct; Moissanite (true weight): 0.030 ct; Sapphire: 0.030 ct

2.5 mm: Diamond weight: 0.060 ct; Moissanite (true weight): 0.050 ct; Sapphire: 0.070 ct

3 mm: Diamond weight: 0.1 ct; Moissanite (true weight): 0.090 ct; Sapphire: 0.11 ct

3.5 mm: Diamond weight: 0.16 ct; Moissanite (true weight): 0.15 ct; Sapphire: 0.18 ct

4 mm: Diamond weight: 0.24 ct; Moissanite (true weight): 0.22 ct; Sapphire: 0.27 ct

4.5 mm: Diamond weight: 0.34 ct; Moissanite (true weight): 0.31 ct; Sapphire: 0.39 ct

5 mm: Diamond weight: 0.47 ct; Moissanite (true weight): 0.43 ct; Sapphire: 0.53 ct

5.5 mm: Diamond weight: 0.62 ct; Moissanite (true weight): 0.57 ct; Sapphire: 0.7 ct

6 mm: Diamond weight: 0.8 ct; Moissanite (true weight): 0.74 ct; Sapphire: 0.91 ct

6.5 mm: Diamond weight: 1.02 ct; Moissanite (true weight): 0.94 ct; Sapphire: 1.16 ct

7 mm: Diamond weight: 1.28 ct; Moissanite (true weight): 1.17 ct; Sapphire: 1.45 ct

8 mm: Diamond weight: 1.91 ct; Moissanite (true weight): 1.75 ct; Sapphire: 2.17 ct

9 mm: Diamond weight: 2.72 ct; Moissanite (true weight): 2.49 ct; Sapphire: 3.09 ct

10 mm: Diamond weight: 3.73 ct; Moissanite (true weight): 3.41 ct; Sapphire: 4.23 ct

Size	Diamond weight	Moissanite (true weight)	Sapphire
1 mm	0.0000 ct	0.0000 ct	0.0000 ct
1.5 mm	0.010 ct	0.010 ct	0.010 ct
2 mm	0.030 ct	0.030 ct	0.030 ct
2.5 mm	0.060 ct	0.050 ct	0.070 ct
3 mm	0.1 ct	0.090 ct	0.11 ct
3.5 mm	0.16 ct	0.15 ct	0.18 ct
4 mm	0.24 ct	0.22 ct	0.27 ct
4.5 mm	0.34 ct	0.31 ct	0.39 ct
5 mm	0.47 ct	0.43 ct	0.53 ct
5.5 mm	0.62 ct	0.57 ct	0.7 ct
6 mm	0.8 ct	0.74 ct	0.91 ct
6.5 mm	1.02 ct	0.94 ct	1.16 ct
7 mm	1.28 ct	1.17 ct	1.45 ct
8 mm	1.91 ct	1.75 ct	2.17 ct
9 mm	2.72 ct	2.49 ct	3.09 ct
10 mm	3.73 ct	3.41 ct	4.23 ct

Oval calibrated sizes

5 x 3 mm: Diamond weight: 0.2 ct; Moissanite (true weight): 0.18 ct; Sapphire: 0.23 ct

6 x 4 mm: Diamond weight: 0.4 ct; Moissanite (true weight): 0.37 ct; Sapphire: 0.46 ct

7 x 5 mm: Diamond weight: 0.71 ct; Moissanite (true weight): 0.65 ct; Sapphire: 0.81 ct

8 x 6 mm: Diamond weight: 1.14 ct; Moissanite (true weight): 1.04 ct; Sapphire: 1.29 ct

9 x 7 mm: Diamond weight: 1.71 ct; Moissanite (true weight): 1.57 ct; Sapphire: 1.95 ct

10 x 8 mm: Diamond weight: 2.45 ct; Moissanite (true weight): 2.24 ct; Sapphire: 2.79 ct

11 x 9 mm: Diamond weight: 3.38 ct; Moissanite (true weight): 3.09 ct; Sapphire: 3.84 ct

12 x 10 mm: Diamond weight: 4.5 ct; Moissanite (true weight): 4.12 ct; Sapphire: 5.12 ct

14 x 10 mm: Diamond weight: 5.68 ct; Moissanite (true weight): 5.19 ct; Sapphire: 6.45 ct

Size	Diamond weight	Moissanite (true weight)	Sapphire
5 x 3 mm	0.2 ct	0.18 ct	0.23 ct
6 x 4 mm	0.4 ct	0.37 ct	0.46 ct
7 x 5 mm	0.71 ct	0.65 ct	0.81 ct
8 x 6 mm	1.14 ct	1.04 ct	1.29 ct
9 x 7 mm	1.71 ct	1.57 ct	1.95 ct
10 x 8 mm	2.45 ct	2.24 ct	2.79 ct
11 x 9 mm	3.38 ct	3.09 ct	3.84 ct
12 x 10 mm	4.5 ct	4.12 ct	5.12 ct
14 x 10 mm	5.68 ct	5.19 ct	6.45 ct

Cushion calibrated sizes

4 x 4 mm: Diamond weight: 0.36 ct; Moissanite (true weight): 0.33 ct; Sapphire: 0.41 ct

5 x 5 mm: Diamond weight: 0.71 ct; Moissanite (true weight): 0.65 ct; Sapphire: 0.81 ct

6 x 6 mm: Diamond weight: 1.23 ct; Moissanite (true weight): 1.13 ct; Sapphire: 1.4 ct

7 x 7 mm: Diamond weight: 1.95 ct; Moissanite (true weight): 1.79 ct; Sapphire: 2.22 ct

8 x 8 mm: Diamond weight: 2.92 ct; Moissanite (true weight): 2.67 ct; Sapphire: 3.31 ct

9 x 9 mm: Diamond weight: 4.15 ct; Moissanite (true weight): 3.8 ct; Sapphire: 4.72 ct

10 x 10 mm: Diamond weight: 5.69 ct; Moissanite (true weight): 5.21 ct; Sapphire: 6.47 ct

Size	Diamond weight	Moissanite (true weight)	Sapphire
4 x 4 mm	0.36 ct	0.33 ct	0.41 ct
5 x 5 mm	0.71 ct	0.65 ct	0.81 ct
6 x 6 mm	1.23 ct	1.13 ct	1.4 ct
7 x 7 mm	1.95 ct	1.79 ct	2.22 ct
8 x 8 mm	2.92 ct	2.67 ct	3.31 ct
9 x 9 mm	4.15 ct	3.8 ct	4.72 ct
10 x 10 mm	5.69 ct	5.21 ct	6.47 ct

Princess calibrated sizes

3 mm: Diamond weight: 0.16 ct; Moissanite (true weight): 0.15 ct; Sapphire: 0.18 ct

4 mm: Diamond weight: 0.38 ct; Moissanite (true weight): 0.35 ct; Sapphire: 0.44 ct

5 mm: Diamond weight: 0.75 ct; Moissanite (true weight): 0.69 ct; Sapphire: 0.85 ct

6 mm: Diamond weight: 1.3 ct; Moissanite (true weight): 1.19 ct; Sapphire: 1.48 ct

7 mm: Diamond weight: 2.06 ct; Moissanite (true weight): 1.89 ct; Sapphire: 2.34 ct

8 mm: Diamond weight: 3.08 ct; Moissanite (true weight): 2.82 ct; Sapphire: 3.5 ct

Size	Diamond weight	Moissanite (true weight)	Sapphire
3 mm	0.16 ct	0.15 ct	0.18 ct
4 mm	0.38 ct	0.35 ct	0.44 ct
5 mm	0.75 ct	0.69 ct	0.85 ct
6 mm	1.3 ct	1.19 ct	1.48 ct
7 mm	2.06 ct	1.89 ct	2.34 ct
8 mm	3.08 ct	2.82 ct	3.5 ct

Emerald cut calibrated sizes

5 x 3 mm: Diamond weight: 0.28 ct; Moissanite (true weight): 0.26 ct; Sapphire: 0.32 ct

6 x 4 mm: Diamond weight: 0.57 ct; Moissanite (true weight): 0.52 ct; Sapphire: 0.65 ct

7 x 5 mm: Diamond weight: 1 ct; Moissanite (true weight): 0.91 ct; Sapphire: 1.14 ct

8 x 6 mm: Diamond weight: 1.61 ct; Moissanite (true weight): 1.47 ct; Sapphire: 1.83 ct

9 x 7 mm: Diamond weight: 2.41 ct; Moissanite (true weight): 2.21 ct; Sapphire: 2.74 ct

10 x 8 mm: Diamond weight: 3.46 ct; Moissanite (true weight): 3.16 ct; Sapphire: 3.93 ct

Size	Diamond weight	Moissanite (true weight)	Sapphire
5 x 3 mm	0.28 ct	0.26 ct	0.32 ct
6 x 4 mm	0.57 ct	0.52 ct	0.65 ct
7 x 5 mm	1 ct	0.91 ct	1.14 ct
8 x 6 mm	1.61 ct	1.47 ct	1.83 ct
9 x 7 mm	2.41 ct	2.21 ct	2.74 ct
10 x 8 mm	3.46 ct	3.16 ct	3.93 ct

Pear calibrated sizes

5 x 3 mm: Diamond weight: 0.18 ct; Moissanite (true weight): 0.17 ct; Sapphire: 0.21 ct

6 x 4 mm: Diamond weight: 0.37 ct; Moissanite (true weight): 0.34 ct; Sapphire: 0.42 ct

7 x 5 mm: Diamond weight: 0.65 ct; Moissanite (true weight): 0.59 ct; Sapphire: 0.74 ct

8 x 5 mm: Diamond weight: 0.79 ct; Moissanite (true weight): 0.72 ct; Sapphire: 0.9 ct

9 x 6 mm: Diamond weight: 1.24 ct; Moissanite (true weight): 1.14 ct; Sapphire: 1.41 ct

10 x 7 mm: Diamond weight: 1.83 ct; Moissanite (true weight): 1.68 ct; Sapphire: 2.08 ct

Size	Diamond weight	Moissanite (true weight)	Sapphire
5 x 3 mm	0.18 ct	0.17 ct	0.21 ct
6 x 4 mm	0.37 ct	0.34 ct	0.42 ct
7 x 5 mm	0.65 ct	0.59 ct	0.74 ct
8 x 5 mm	0.79 ct	0.72 ct	0.9 ct
9 x 6 mm	1.24 ct	1.14 ct	1.41 ct
10 x 7 mm	1.83 ct	1.68 ct	2.08 ct

Marquise calibrated sizes

6 x 3 mm: Diamond weight: 0.19 ct; Moissanite (true weight): 0.18 ct; Sapphire: 0.22 ct

8 x 4 mm: Diamond weight: 0.46 ct; Moissanite (true weight): 0.42 ct; Sapphire: 0.52 ct

10 x 5 mm: Diamond weight: 0.89 ct; Moissanite (true weight): 0.81 ct; Sapphire: 1.01 ct

12 x 6 mm: Diamond weight: 1.54 ct; Moissanite (true weight): 1.41 ct; Sapphire: 1.75 ct

Size	Diamond weight	Moissanite (true weight)	Sapphire
6 x 3 mm	0.19 ct	0.18 ct	0.22 ct
8 x 4 mm	0.46 ct	0.42 ct	0.52 ct
10 x 5 mm	0.89 ct	0.81 ct	1.01 ct
12 x 6 mm	1.54 ct	1.41 ct	1.75 ct

Heart calibrated sizes

4 mm: Diamond weight: 0.23 ct; Moissanite (true weight): 0.21 ct; Sapphire: 0.26 ct

5 mm: Diamond weight: 0.46 ct; Moissanite (true weight): 0.42 ct; Sapphire: 0.52 ct

6 mm: Diamond weight: 0.79 ct; Moissanite (true weight): 0.72 ct; Sapphire: 0.89 ct

7 mm: Diamond weight: 1.25 ct; Moissanite (true weight): 1.14 ct; Sapphire: 1.42 ct

8 mm: Diamond weight: 1.86 ct; Moissanite (true weight): 1.71 ct; Sapphire: 2.12 ct

Size	Diamond weight	Moissanite (true weight)	Sapphire
4 mm	0.23 ct	0.21 ct	0.26 ct
5 mm	0.46 ct	0.42 ct	0.52 ct
6 mm	0.79 ct	0.72 ct	0.89 ct
7 mm	1.25 ct	1.14 ct	1.42 ct
8 mm	1.86 ct	1.71 ct	2.12 ct

Questions

A stone cut to a standard size in mm so it fits ready-made settings. Calibrated sizes are given as a diameter, or a length and width.

A round 7 mm diamond is about 1.28 carat. A 7 mm sapphire is about 1.45 carat, since sapphire is denser.

Each gem has its own density. The same volume weighs more in a denser gem such as sapphire and less in a lighter one such as aquamarine.