Carats are the traditional measuring unit of a diamond's weight
Carats are the traditional measuring unit of a diamond's weight, one carat equaling 200 milligrams, in other words one gram equaling five carats. A carat is divided into 100 'points,' like one dollar divided into 100 cents, so the same diamond can be represented as weighing a carat and a half, 150 points or 1.50 carats.
Two terms, carat and karat are often confused. Karat refers to the fineness of gold alloys (pure gold is 24 karat; 14 karat or 14Kt. is 14 parts gold and 10 parts other metals) and Carat refers to gem weights, 1.05 Carat or 1.05 Ct.
Carat Weight
Used in weighing precious and semi-precious stones. (the term “Karat” refers to the quality of purity in gold.)
1 carat = 31/16 grains Troy
1 carat = .007 ounce Acoir
1 carat = 1/5 gram
The carat is further divided into points for simple measurement:
1 carat = 100 points
½ carat = 50 points
¼ carat = 25 points
1/8 carat = 12 ½ points
Image on left helps you visualize how a diamond's carat weight translates into diamond size using a diagram that illustrates round brilliant cut diamonds of ideal proportions. ( Click on image to enlarge )
Jewelry Guide: Millimeter to Inch Converter Chart. ( Click on link )
Diamond Carat Weight / Diameter mm. size Table :
The following table gives an approximate guide to the relative size in millimetres, and weight of modern round brilliant cut and fancy cut diamonds of ideal proportions.
 |
Round Cut |
| Milimeters |
Carat weight |
Points / Cents |
| 1.0 |
0.005 |
0.5 |
| 1.3 |
0.01 |
1 |
| 1.5 |
0.015 |
1.5 |
| 1.7 |
0.02 |
1 |
| 1.8 |
0.025 |
2.5 |
| 2.0 |
0.03 |
3 |
| 2.1 |
0.035 |
3.5 |
| 2.2 |
0.04 |
4 |
| 2.4 |
0.05 |
5 |
| 2.5 |
0.06 |
6 |
| 2.7 |
0.07 |
7 |
| 2.8 |
0.08 |
8 |
| 2.9 |
0.09 |
9 |
| 3.0 |
0.10 |
10 |
| 3.1 |
0.11 |
11 |
| 3.2 |
0.12 |
12 |
| 3.3 |
0.14 |
14 |
| 3.4 |
0.15 |
15 |
| 3.5 |
0.16 |
16 |
| 3.6 |
0.17 |
17 |
| 3.7 |
0.18 |
18 |
| 3.8 |
0.20 |
20 |
| 3.9 |
0.22 |
22 |
| 4.0 |
0.25 |
25 |
| 4.2 |
0.30 |
30 |
| 4.4 |
0.33 |
33 |
| 4.5 |
0.35 |
35 |
| 4.6 |
0.38 |
38 |
| 4.8 |
0.40 |
40 |
| 5.0 |
0.50 |
50 |
| 5.4 |
0.60 |
60 |
| 5.5 |
0.63 |
63 |
| 5.6 |
0.65 |
65 |
| 6.0 |
0.75 |
75 |
| 6.4 |
0.95 |
95 |
| 6.6 |
1.00 |
100 |
| 6.8 |
1.17 |
117 |
| 7.0 |
1.25 |
125 |
| 7.2 |
1.33 |
133 |
| 7.5 |
1.55 |
155 |
| 7.8 |
1.75 |
175 |
| 8.0 |
2.00 |
200 |
| 8.4 |
2.15 |
215 |
| 8.6 |
2.25 |
225 |
| 9.0 |
2.75 |
275 |
| 9.4 |
3.00 |
300 |
| 9.6 |
3.15 |
315 |
| 9.8 |
3.35 |
335 |
| 10.0 |
3.50 |
350 |
| 10.2 |
3.75 |
375 |
| 10.4 |
4.00 |
400 |
| 10.6 |
4.25 |
425 |
| 10.8 |
4.5 |
450 |
| 11.0 |
4.75 |
475 |
| 11.2 |
5.00 |
500 |
| 12.0 |
6.50 |
650 |
 |
Oval Cut |
| Milimeters |
Carat weight |
Points |
| 4 x 3 |
0.20 |
20 |
| 5 x 3 |
0.25 |
25 |
| 5 x 3.5 |
0.33 |
33 |
| 5 x 4 |
0.40 |
40 |
| 6 x 4 |
0.50 |
50 |
| 6.5 x 4.5 |
0.65 |
65 |
| 7 x 5 |
0.75 |
75 |
| 7.5 x 5.5 |
1.00 |
100 |
| 8 x 6 |
1.25 |
125 |
| 8.5 x 6.5 |
1.50 |
150 |
| 9 x 6 |
1.75 |
175 |
| 9 x 7 |
2.00 |
200 |
| 9.5 x 7.5 |
2.5 |
250 |
| 10 x 8 |
3.00 |
300 |
| 10 x 8.5 |
3.5 |
350 |
| 11 x 9 |
4.00 |
400 |
| 11 x 9.5 |
4.50 |
450 |
| 12 x 10 |
5.00 |
500 |
 |
Marquise Cut |
| Milimeters |
Carat weight |
Points |
| 3.5 x 1.5 |
0.07 |
7 |
| 4 x 2 |
0.10 |
10 |
| 5 x 2 |
0.20 |
20 |
| 5 x 3 |
0.22 |
22 |
| 5.5 x 2.5 |
0.25 |
25 |
| 6 x 6 |
0.30 |
30 |
| 7 x 3 |
0.35 |
35 |
| 7 x 3.5 |
0.38 |
38 |
| 7 x 4 |
0.40 |
40 |
| 8 x 4 |
0.50 |
50 |
| 8.5 x 4.5 |
0.65 |
65 |
| 9 x 4 |
.70 |
70 |
| 9 x 4.5 |
0.75 |
75 |
| 9 x 5 |
0.80 |
80 |
| 9.5 x 4.5 |
0.85 |
85 |
| 10 x 4.75 |
1.00 |
100 |
| 10 x 5 |
1.25 |
125 |
| 11 x 5 |
1.50 |
150 |
| 11 x 5.5 |
1.65 |
165 |
| 12 x 6 |
2.00 |
200 |
| 13 x 5.5 |
2.50 |
250 |
| 13 x 6 |
2.65 |
265 |
| 14 x 6.5 |
2.87 |
287 |
| 14 x 7 |
3.00 |
300 |
| 15 x 7 |
3.75 |
375 |
| 16 x 8 |
4.50 |
450 |
| 18 x 9 |
7.00 |
700 |
| 20 x 10 |
10 |
1000 |
 |
Princess Cut |
| Milimeters |
Carat weight |
Points |
| 2.00 |
0.06 |
6 |
| 2.25 |
0.08 |
8 |
| 2.50 |
0.10 |
10 |
| 2.75 |
0.13 |
13 |
| 3.0 |
0.15 |
15 |
| 3.25 |
0.20 |
20 |
| 3.5 |
0.23 |
23 |
| 3.75 |
0.25 |
25 |
| 4.0 |
0.30 |
30 |
| 4.42 |
0.35 |
35 |
| 4.5 |
0.40 |
40 |
| 4.75 |
0.50 |
50 |
| 5.0 |
0.63 |
63 |
| 5.25 |
0.75 |
75 |
| 5.5 |
1.00 |
100 |
| 6.0 |
1.25 |
125 |
| 7.0 |
1.60 |
160 |
| 8.0 |
2.25 |
225 |
 |
Emerald Cut |
| Milimeters |
Carat weight |
Points |
| 4 x 3 |
0.20 |
20 |
| 5 x 3 |
0.25 |
25 |
| 6 x4 |
0.50 |
50 |
| 6.5 x 4.5 |
0.75 |
75 |
| 7 x 5 |
1.00 |
100 |
| 8 x 6 |
1.50 |
150 |
| 8.5 x 6.5 |
2.00 |
200 |
| 9 x 7 |
2.50 |
250 |
| 10 x 8 |
3.00 |
300 |
| 11 x 9 |
4.00 |
400 |
| 12 x 10 |
5.00 |
500 |
 |
Pear Cut |
| Milimeters |
Carat weight |
Points |
| 4 x 2 |
0.20 |
20 |
| 5 x 3 |
0.30 |
30 |
| 6 x 4 |
0.50 |
50 |
| 7 x 5 |
0.75 |
75 |
| 8 x 5 |
1.00 |
100 |
| 9 x 6 |
1.50 |
150 |
| 10 x 7 |
2.00 |
200 |
| 12 x 7 |
2.50 |
250 |
| 12 x 8 |
3.00 |
300 |
| 13 x 8 |
3.50 |
350 |
| 14 x 8 |
4.00 |
400 |
| 15 x 9 |
5.00 |
500 |
