One of the most frequent questions we get when discussing the purchase of loose diamonds is "How big is a 1ct diamond?" From the Four Cs of Diamonds, two of the Cs play an important role here when talking "size" - carat weight and cut.

"Carat weight" is the physical weight of a diamond therefore a 1ct diamond weighs 1ct (100 points). Depending on the shape and cut of the diamond, the diamond can appear to be larger or smaller. This is where the cut comes into play along with the depth of the stone. A stone with a deep cut, displays smaller because the stone is "taller" and more narrow. A shallow cut diamond will measure larger, however the light and sparkle with be less than an "ideal cut" diamond.

To best estimate carat size and mm size, it's easiest to use ideal cut diamonds. Ideal cut diamonds are cut to maximize the brilliance of a diamond by allowing the light to reflect perfectly.

The diamond measurement charts below show some approximations of carat weight and physical measurements. And remember, as cut can vary tremendously, these are only general approximations based on ideal cut diamonds.

 

Diamond Carat Weight to Size Chart

 

Round Brilliant Sizing

MM Size	Carat Weight	MM Size	Carat Weight
0.8	0.0025	7	1.28
1	0.005	7.25	1.49
1.12	0.0075	7.5	1.67
1.15	0.0067	7.75	1.75
1.25	0.01	8	2.04
1.3	0.01	8.25	2.11
1.5	0.015	8.5	2.43
1.75	0.02	8.75	2.55
1.8	0.025	9	2.75
2	0.03	9.25	3.05
2.25	0.04	9.5	3.35
2.5	0.06	9.75	3.61
2.75	0.08	10	3.87
3	0.11	10.25	4.16
3.25	0.14	10.5	4.41
3.5	0.17	10.75	4.57
3.75	0.21	11	4.91
4	0.25	11.25	5.49
4.25	0.28	11.5	5.85
4.5	0.36	12	6.84
4.75	0.44	12.25	7.26
5	0.46	12.5	7.36
5.25	0.56	12.75	7.52
5.5	0.66	13	8.51
5.75	0.76	13.5	9.53
6	0.84	14	10.49
6.25	0.93	15	12.89
6.5	1.03	16	16.06
6.75	1.24

 

Princess Cut Sizing

MM Size	Carat Weight	MM Size	Carat Weight
1.5	0.015	6.5	1.59
1.75	0.03	6.75	1.75
2	0.06	7	1.96
2.25	0.08	7.25	2.01
2.5	0.1	7.5	2.4
2.75	0.13	7.75	2.74
3	0.18	8	3.01
3.25	0.26	8.25	3.24
3.5	0.29	8.5	3.67
3.75	0.31	8.75	4.1
4	0.39	9	4.12
4.25	0.44	9.5	5.09
4.5	0.56	9.75	5.36
4.75	0.64	10	5.62
5	0.71	10.25	5.76
5.25	0.75	10.5	5.99
5.5	0.99	11	7.44
5.75	1.11	11.5	9.44
6	1.24	12	9.52
6.25	1.39

 

Asscher Cut Sizing

MM Size	Carat Weight	MM Size	Carat Weight
4	0.39	8	3.01
4.5	0.56	8.5	3.67
5	0.71	9	4.12
5.5	0.99	9.5	5.09
6	1.24	10	5.62
6.5	1.59	11	7.44
7	1.96	12	9.52
7.5	2.4	13	12.66

 

Marquise Sizing

MM Size	Carat Weight	MM Size	Carat Weight
3 x 1.5	0.025	9.5 x 2	0.85
3.5 x 1.75	0.065	10 x 5	0.95
3.5 x 2	0.07	11 x 5.5	1.25
3.75 x 1.75	0.11	11.5 x 6	1.33
4 x 2	0.1	12 x 6	1.62
4.25 x 2.25	0.12	12 x 6.5	1.71
5 x 2.5	0.14	13 x 6.5	2.11
5 x 3	0.2	14 x 7	2.48
5.5 x 2.75	0.16	15 x 7.5	3.09
5.5 x 3	0.18	14 x 8	3
6 x 3	0.25	15 x 7	3.12
6.5 x 3	0.23	15 x 8	3.44
7 x 3	0.3	16 x 8	3.86
7 x 3.5	0.35	17 x 8.5	4.88
7 x 4	3.4	17.5 x 10	5.5
7.5 x 3.5	0.33	20 x 8	7.08
8 x 4	0.47	20 x 10	7.94
9 x 4.5	0.71	20 x 11	9.5
9 x 5	0.76

 

Radiant Cut Sizing

MM Size	Carat Weight	MM Size	Carat Weight
4.5 x 3.5	0.34	10 x 8	3.49
5 x 3	0.31	11 x 9	5.05
6 x 3	0.41	11.5 x 10	6.45
6 x 4	0.6	12 x 9	6.06
6.5 x 4.5	0.83	12 x 10	6.79
7 x 5	1.14	13 x 9	6.54
7.25 x 5.25	1.24	13 x 11	9.33
7.5 x 5.5	1.47	13.5 x 11.5	10.19
8 x 6	1.74	14 x 10	8.47
8.5 x 6.5	2.25	14 x 12	12.14
9 x 7	2.62	15 x 11	11.48
9.5 x 7.5	3.18	16 x 12	14.22
10 x 7	3.31

 

Cushion Cut Sizing

MM Size	Carat Weight	MM Size	Carat Weight
4	0.25	8	2.04
4.5	0.36	8.5	2.43
5	0.46	9	2.75
5.25	0.56	9.5	3.35
5.5	0.66	10	3.87
5.75	0.76	10.5	4.41
6	0.84	11	4.91
6.25	0.93	11.5	5.85
6.5	1.03	12	6.84
6.75	1.24	13	8.51
7	1.28	14	10.49
7.5	1.67	15	12.89

 

Pear Shape Sizing

MM Size	Carat Weight	MM Size	Carat Weight
3 x 2	0.13	12 x 8	3
4 x 2.5	0.18	12 x 9	3.44
4 x 3	0.21	13 x 8	2.98
5 x 3	0.25	14 x 8	3.47
5 x 4	0.35	13 x 9	4.11
6 x 4	0.39	14 x 9	4.25
6.5 x 4.5	0.57	15 x 9	5.06
7 x 5	0.71	14 x 10	5.41
8 x 5	0.81	13 x 11	5.65
8.5 x 5.5	1.08	15 x 10	5.75
8 x 6	1.25	15 x 11	7.36
9 x 6	1.33	16 x 9	5.86
9 x 7	1.75	16 x 10	6.27
10 x 6	1.71	16 x 12	8.99
10 x 7	1.8	17 x 10	6.46
10 x 8	2.46	18 x 11	8.14
11 x 7.50	2.61	18 x 12	9.35
11 x 8	3	18 x 13	10.21
12 x 7	3.12

 

Oval Shape Sizing

MM Size	Carat Weight	MM Size	Carat Weight
4.5 x 3.5	0.21	10 x 8	2.54
5 x 3	0.21	10.5 x 8.5	2.88
5 x 4	0.35	11 x 9	3.85
5.5 x 3.5	0.33	12 x 8	2.99
6 x 4	0.43	12 x 10	5.05
6.5 x 4.5	0.65	14 x 10	5.81
6 x 5	0.61	13 x 11	6.05
7 x 5	0.76	14 x 12	8.21
7.5 x 5.5	0.98	15 x 12	8.76
8 x 6	1.21	16 x 12	9.32
8.5 x 6.5	1.46	16 x 14	11.88
9 x 6	1.41	18 x 13	12.86
9 x 7	1.86	20 x 15	14.96

 

Heart Shape Sizing

MM Size	Carat Weight	MM Size	Carat Weight
3.5	0.18	8	1.71
4	0.25	9	2.41
4.25	0.28	9.5	2.9
4.5	0.34	10	3.16
4.75	0.38	11	4.41
5	0.44	12	5.66
5.5	0.61	13	7.88
6	0.74	14	9.38
6.25	0.83	15	10.79
6.5	0.93	16	13.27
7	1.13	18	15.33
7.5	1.59

 

Trillion Sizing

MM Size	Carat Weight	MM Size	Carat Weight
3	0.12	6.25	0.75
3.5	0.16	6.5	0.91
3.75	0.19	6.75	0.98
4	0.23	7	1.1
4.25	0.27	7.5	1.21
4.5	0.31	8	1.75
4.75	0.37	9	2.35
5	0.42	11	3.66
5.25	0.49	12	4.9
5.5	0.55	13	6.42
5.75	0.64	15	9
6	0.7

 

Emerald Cut Sizing

MM Size	Carat Weight	MM Size	Carat Weight
3 x 2	0.1	9 x 7	2.62
3.5 x 2	0.12	9.5 x 7.5	3.21
4 x 2	0.15	10 x 7	3.01
4 x 3	0.2	10 x 8	3.79
5 x 3	0.29	11 x 9	5.21
5.5 x 3.5	0.46	12 x 8	5.34
5.5 x 4	0.48	12 x 10	6
6 x 4	0.66	13 x 9	6.38
6.5 x 4.5	0.88	14 x 8	6.25
7 x 5	1.06	14 x 10	8.48
7.25 x 5.25	1.24	13 x 11	9.13
7.5 x 5.5	1.45	14 x 12	11.26
8 x 6	1.74	16 x 12	14.22
8.5 x 6.5	2.17

 

Triangle Cut Sizing

MM Size	Carat Weight	MM Size	Carat Weight
2.5	0.08	7	1.11
3	0.12	7.25	1.32
3.5	0.18	7.5	1.45
4	0.25	7.75	1.69
4.25	0.32	8	1.79
4.5	0.37	8.25	1.86
4.75	0.42	9	2.15
5	0.45	9.25	2.54
5.25	0.53	9.75	3.25
5.5	0.66	10	3.52
5.75	0.71	11	4.74
6	0.76	12	6.03
6.25	0.86	13	8.12
6.5	0.94	14	9.83
6.75	1.02

 

Tapered Baguette Sizing

MM Size	Carat Weight	MM Size	Carat Weight
2 x 1.5 x 1	0.025	4.25 x 2 x 1.5	0.13
2.5 x 1.5 x 1	0.035	4.25 x 2.5 x 1.25	0.13
2.5 x 1.75 x 1	0.04	4.25 x 2.5 x 1.5	0.135
3 x 1.5 x 1	0.05	4.5 x 1.75 x 1.25	0.15
3 x 1.75 x 1.25	0.055	4.5 x 2 x 1.5	0.12
3 x 1.75 x 1.3	0.055	4.5 x 2.3 x 1.8	0.16
3 x 1.75 x 1.5	0.055	4.5 x 2.5 x 2	0.15
3 x 2 x 1	0.06	4.5 x 2.75 x 1.75	0.15
3 x 2 x 1.25	0.065	4.5 x 3 x 2	0.16
3 x 2 x 1.5	0.07	4.5 x 3 x 2.5	0.16
3 x 2 x 1.75	0.075	4.75 x 2.5 x 1.5	0.15
3 x 2.5 x 2	0.08	4.75 x 3 x 2	0.18
3.25 x 1.75 x 1	0.07	5 x 2 x 1	0.14
3.25 x 1.75 x 1.25	0.05	5 x 2 x 1.25	0.15
3.5 x 1.25 x 1	0.04	5 x 2 x 1.5	0.15
3.5 x 1.5 x 1	0.05	5 x 2.3 x 1.8	0.16
3.5 x 1.5 x 1.25	0.055	5 x 2.5 x 1.5	0.2
3.5 x 1.7 x 1.3	0.055	5 x 2.5 x 2	0.21
3.5 x 1.75 x 1	0.06	5 x 2.75 x 2	0.21
3.5 x 1.75 x 1.25	0.07	5 x 3 x 2	0.25
3.5 x 1.75 x 1.3	0.065	5 x 3.5 x 2	0.26
3.5 x 2 x 1.25	0.08	5 x 4 x 3.5	0.28
3.5 x 2 x 1.5	0.09	5.5 x 2 x 1.5	0.18
3.5 x 2.5 x 2	0.09	5.5 x 2.5 x 1.75	0.23
3.75 x 2 x 1.25	0.08	5.5 x 2.5 x 2	0.23
4 x 1.5 x 1	0.07	5.5 x 3 x 2	0.26
4 x 1.5 x 1.2	0.08	5.5 x 3 x 2.25	0.26
4 x 1.75 x 1.25	0.08	5.5 x 4 x 2.5	0.28
4 x 2 x 1.5	0.1	6 x 2 x 1.5	0.3
4 x 2.5 x 1.5	0.12	6 x 2.5 x 1.5	0.3
4 x 2.5 x 2	0.21	6 x 3 x 2	0.3
4 x 3 x 2	0.21	6.5 x 2.5 x 2	0.3
4.25 x 2 x 1.25	0.11	6.5 x 3 x 2	0.32

 

Rectangular Baguette Sizing

MM Size	Carat Weight	MM Size	Carat Weight
2 x 1	0.02	3.75 x 1.5	0.14
2 x 1.5	0.04	3.75 x 2	0.145
2 x 1.75	0.04	4 x 1.25	0.075
2.25 x 1.75	0.04	4 x 1.5	0.08
2.25 x 2	0.045	4 x 1.75	0.11
2.5 x 1	0.045	4 x 2	0.14
2.5 x 1.25	0.047	4 x 3	0.2
2.5 x 1.5	0.05	4.5 x 1.5	0.1
2.5 x 1.75	0.055	4.5 x 1.75	0.14
2.5 x 2	0.055	4.5 x 2	0.17
2.75 x 1.5	0.055	4.5 x 2.5	0.2
2.75 x 1.75	0.06	4.5 x 3	0.285
2.75 x 2	0.06	4.5 x 3.5	0.3
2.75 x 2.5	0.065	4.75 x 1.5	0.27
3 x 1	0.05	4.75 x 2	0.28
3 x 1.25	0.055	5 x 1.5	0.14
3 x 1.5	0.06	5 x 1.75	0.15
3 x 1.75	0.08	5 x 2	0.19
3 x 2	0.1	5 x 2.5	0.24
3 x 2.5	0.13	5 x 3	0.3
3.25 x 1.25	0.06	5 x 3.5	0.33
3.25 x 1.5	0.065	5 x 4	0.4
3.25 x 1.75	0.08	5.5 x 1.75	0.16
3.25 x 2.5	0.14	5.5 x 2	0.18
3.5 x 1	0.065	5.5 x 2.5	0.23
3.5 x 1.25	0.07	5.5 x 3	0.3
3.5 x 1.5	0.07	5.5 x 3.5	0.33
3.5 x 1.75	0.08	6 x 1.75	0.28
3.5 x 2	0.13	6 x 2	0.3
3.5 x 2.5	0.15	6 x 2.5	0.33
3.5 x 3	0.15	6 x 3	0.4