Diamond Sizes in MM

Round

Princess
Cushion
Oval
Emerald
Heart
Pear
Marquise

If you know your ring size but have a different number than those used in Belgium (ISO 8653:2016, which defines the number in terms of internal circumference), use the table below to convert your size. We also recommend cross-referencing your ring size by measuring the ring’s internal diameter and/or internal circumference. Wondering what a 1 carat round diamond looks like on a hand? Our round diamond size chart will help you convert millimeter (mm) size to carat size for round cut diamonds.
Visit our Select a Diamond page to explore our extensive collection of loose diamonds. Find the perfect diamond that matches your style and budget, and take the first step towards creating your dream jewelry piece today!

ROUND MM SIZE	ROUND CARAT WEIGHT	BLACK DIAMONDS CT. WEIGHT
0.8 mm.	0.0025 ct.	0.00
1 mm.	0.005 ct.	0.01
1.1 mm.	0.0067 ct.	0.01
1.2 mm.	0.009 ct.	0.01
1.25 mm.	0.01 ct.	0.01
1.3 mm.	0.01 ct.	0.01
1.5 mm.	0.015 ct.	0.02
1.75 mm.	0.02 ct.	0.02
1.8 mm.	0.025 ct.	0.03
2 mm.	0.03 ct.	0.04
2.2 mm.	0.04 ct.	0.05
2.5 mm.	0.06 ct.	0.07
2.75 mm	0.08 ct.	0.10
3 mm.	0.10 ct.	0.12
3.25 mm.	0.14 ct.	0.17
3.5 mm.	0.17 ct.	0.20
3.75 mm.	0.21 ct.	0.25
4 mm	0.25 ct.	0.33
4.25 mm.	0.28 ct.	0.36
4.5 mm.	0.36 ct.	0.47
4.75 mm.	0.44 ct.	0.57
5.0 mm.	0.50 ct.	0.65
5.25 mm.	0.56 ct.	0.73
5.5 mm.	0.66 ct.	0.89
5.75 mm.	0.75 ct.	1.01
6 mm.	0.84 ct.	1.20
6.25 mm.	0.93 ct.	1.30
6.5 mm.	1.00 ct	1.40
6.8 mm.	1.25 ct.	1.80
7 mm.	1.30 ct.	1.90
7.3 mm.	1.50 ct.	2.10
7.5 mm.	1.67 ct.	2.40
7.75 mm.	1.75 ct.	2.50
8 mm.	2.00 ct.	2.80
8.25 mm.	2.11 ct.	3.00
8.5 mm.	2.43 ct.	3.50
8.7 mm.	2.50 ct.	3.50
9 mm.	2.75 ct.	3.90
9.1 mm.	3.00 ct.	4.20
9.5 mm.	3.35 ct.	4.70
9.75 mm.	3.61 ct.	5.10
10 mm.	3.87 ct.	5.50
10.25 mm.	4.16 ct.	5.50
10.5 mm.	4.41 ct.	5.80
10.75 mm.	4.57 ct.	6.00
11 mm.	4.91 ct.	6.40
11.25 mm.	5.49 ct.	7.20
11.5 mm.	5.85 ct.	7.70
12 mm.	6.84 ct.	8.90
12.25 mm.	7.26 ct.	9.50
12.5 mm.	7.36 ct.	9.60
12.75 mm.	7.52 ct.	9.80
13 mm.	8.51 ct.	11.10
13.5 mm.	9.53 ct.	12.40
14 mm.	10.49 ct.	13.70
15 mm.	12.89 ct.	16.80
16 mm.	16.06 ct.	20.90

Princess Diamond Sizes

Princess MM Size	Princess Weight (ct)
1.5 mm.	0.02
1.75 mm.	0.03
2 mm.	0.06
2.25 mm.	0.08
2.5 mm.	0.10
2.75 mm.	0.13
3 mm.	0.18
3.25 mm.	0.26
3.5 mm.	0.29
3.75 mm.	0.31
4 mm.	0.39
4.25 mm.	0.44
4.5 mm.	0.50
4.75 mm.	0.64
5 mm.	0.75
5.25 mm.	0.90
5.5 mm.	1.00
5.75 mm.	1.11
6 mm.	1.25
6.25 mm.	1.39
6.5 mm.	1.50
6.75 mm.	1.75
7 mm.	2.00
7.25 mm.	2.01
7.5 mm.	2.50
7.75 mm.	2.74
8 mm.	3.00
8.25 mm.	3.24
8.5 mm.	3.67
8.75 mm.	4.10
9 mm.	4.12
9.5 mm.	5.09
9.75 mm.	5.36
10 mm.	5.62
10.25 mm.	5.76
10.5 mm.	5.99
11 mm.	7.44
11.5 mm.	9.44
12 mm.	9.52

Cushion Diamond Sizes

Cushion MM Size	Cushion Weight (ct)
4.2 mm.	0.40
4.9 mm.	0.50
5.25 mm.	0.75
5.5 mm.	1.00
6 mm.	1.25
6.5 mm.	1.50
7 mm.	2.00
7.5 mm.	2.50
8 mm.	3.00
8.5 mm.	3.50
9 mm.	4.12
9.5 mm.	5.09
10 mm.	5.62
11 mm.	7.44
12 mm.	9.52
13 mm.	12.66

Oval Diamond Sizes

Oval MM Size	Oval Weight (ct)
4.5×3.5 mm.	0.25
5×3 mm.	0.25
5.5×3.5 mm.	0.40
5×4 mm.	0.42
6×4 mm.	0.65
6×5 mm.	0.79
6.5×4.5 mm.	0.85
7×5 mm.	1.00
7.7×5.7 mm.	1.40
8×6 mm.	1.80
9×6 mm.	2.00
8.5×6.5 mm.	2.10
9×7 mm.	2.80
10×8 mm.	3.50
10.5×8.5 mm.	4.10
12×8 mm.	4.20
11×9 mm.	5.40
12×10 mm.	7.10
14×10 mm.	8.20
13×11 mm.	8.50
14×12 mm.	11.50
15×12 mm.	12.30
16×12 mm.	13.10
16×14 mm.	16.70
18×13 mm.	18.10
20×15 mm.	21.00

Emerald Diamond Sizes

Emerald MM Size	Emerald Weight (ct)
3×2 mm.	0.10
3.5×2 mm.	0.12
4×2 mm.	0.15
4×3 mm.	0.20
5×3 mm.	0.29
5.5×3.5 mm.	0.46
6×4 mm.	0.50
6.5×4.5 mm.	0.75
6.7×4.5 mm.	0.88
7×5 mm.	1.00
7.3×5.3 mm.	1.25
7.5×5.5 mm.	1.50
8×6 mm.	1.75
8.5×6.5 mm.	2.00
9×7 mm.	2.50
10×7.5 mm.	3.00
9.5×7.5 mm.	3.21
10×8 mm.	3.79
11×9 mm.	5.21
12×8 mm.	5.34
12×10 mm.	6.00
14×8 mm.	6.25
13×9 mm.	6.38
14×10 mm.	8.48
13×11 mm.	9.13
14×12 mm.	11.26
16×12 mm.	14.22

Heart Diamond Sizes

Heart MM Size	Heart Weight (ct)
3.5 mm.	0.18
4 mm.	0.25
4.25 mm.	0.28
4.5 mm.	0.34
4.75 mm.	0.38
5 mm.	0.50
5.5 mm.	0.61
6 mm.	0.75
6.25 mm.	0.83
6.5 mm.	1.00
7 mm.	1.25
7.5 mm.	1.50
8 mm.	2.00
8.5 mm.	2.50
9 mm.	3.00
10 mm.	3.50
11 mm.	4.41
12 mm.	5.66
13 mm.	7.88
14 mm.	9.38
15 mm.	10.79
16 mm.	13.27
18 mm.	15.33

Pear Diamond Sizes

Pear MM Size	Pear Weight (ct)
3×2 mm.	0.13
4×2.5 mm.	0.18
4×3 mm.	0.21
5×3 mm.	0.25
5×4 mm.	0.35
6×4 mm.	0.50
6.5×4.5 mm.	0.60
7×5 mm.	0.75
7.5×5.5 mm.	0.85
7.7×5.7 mm.	1.00
8.5×6.5 mm.	1.50
8.7×6.7 mm.	1.80
9×7 mm.	2.00
11×7.50 mm.	2.61
13×8 mm.	2.98
11×8 mm.	3.00
12×8 mm.	3.00
12×7 mm.	3.12
12×9 mm.	3.44
14×8 mm.	3.47
13×9 mm.	4.11
14×9 mm.	4.25
15×9 mm.	5.06
14×10 mm.	5.41
13×11 mm.	5.65
15×10 mm.	5.75
16×9 mm.	5.86
16×10 mm.	6.27
17×10 mm.	6.46
15×11 mm.	7.36
18×11 mm.	8.14
16×12 mm.	8.99
18×12 mm.	9.35
18×13 mm.	10.21

Marquise Diamond Sizes

Marquise MM Size	Marquise Weight (ct)
3×1.5 mm.	0.03
3.5×1.75 mm.	0.07
3.5×2 mm.	0.07
4×2 mm.	0.10
3.75×1.75 mm.	0.11
4.25×2.25 mm.	0.12
5×2.5 mm.	0.14
5.5×2.75 mm.	0.16
5.5×3 mm.	0.18
5×3 mm.	0.20
6.5×3 mm.	0.23
6×3 mm.	0.25
7×3 mm.	0.30
7.5×3.5 mm.	0.33
7×4 mm.	0.34
8×4 mm.	0.50
8.75×4.25 mm.	0.70
9×4.5 mm.	0.75
9.5×4.7 mm.	0.85
10×5 mm.	1.00
11×5.5 mm.	1.25
11.5×6 mm.	1.33
12×6 mm.	1.50
13×6.5 mm.	2.00
14×7 mm.	2.50
15×7 mm.	3.00
14×8 mm.	3.00
15×7.5 mm.	3.25
15×8 mm.	3.44
16×8 mm.	3.86
16×8 mm.	3.86
16.5×8.25 mm.	4.00
17×8.5 mm.	4.88
17.5×10 mm.	5.50
20×8 mm.	7.08
20×10 mm.	7.94
20×11 mm.	9.50

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