Proportions charts for Round Brilliant Cut
| Hearts & Arrows Ideal Cut | American Ideal Cut | International Fine Trade Cut | US domestic Average Cut | Below Average Cut | |||||
| Cut classes | Phenomenon | Class 1A | Class 1B | Class 2A | Class 2B | Class 3A | Class 3B | Class 4A | Class 4B |
| Table, % 53%-63% are weght specific in 1A, 1B, 2A grades |
<=.49ct | <=.49ct | <=.49ct | <=.49ct | all weights | all weights | all weights | all weights | all weights |
| 53-57.5 | 53-59 | 59.1-62 52.9-52 |
62.1-63 51.9-51.5 |
63.1-64 51.4-51 |
64.1-67 50.9-50.5 |
67.1-70 50.4-50 |
70.1-72 49.9-49 |
>72 <49 |
|
| >=.50ct | >=.50ct | >=.50ct | >=.50ct | ||||||
| 53-58 | 53-58 | 58.1-60 52.9-52 |
60.1-63 51.9-51.5 |
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| Crown angle, ° | 34.3-34.7 | 34.3-34.7 | 34-34.2 34.8-35 |
32.1-33.9 35.1-35.8 |
31.6-32 35.9-36.4 |
31.5-30.1 36.5-37.9 |
29.6-30 38-39.4 |
29-29.5 39.5-40.5 |
<29 >40.5 |
| Crown height, % | <=.49ct | <=.49ct | <=.49ct | <=.49ct | all weights | all weights | all weights | all weights | all weights |
| 14-16.3 | 14-16.3 | 12.8-13.9 or 16.4-16.8 |
11.6-12.7 or 16.9-17.9 |
11.1-11.5 or 18.0-18.1 |
9.6-11 or 18.2-19.3 |
8.5-9.5 or 19.4-20.5 |
7.8-8.4 or 20.6-21.8 |
<7.8 or >21.8 |
|
| >=.50ct | >=.50ct | >=.50ct | >=.50ct | ||||||
| 14.3-16.3 | 14.3-16.3 | 13.5-14.2 or 16.4-16.8 |
11.6-13.4 or 16.9-17.9 |
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| Pavilion Depth, % | 42.8-43.2 | 42.8-43.2 | 42.5-42.7 43.3-43.5 |
42-42.4 43.6-44 |
41.5-49 44.1-44.9 |
41-41.4 45-45.5 |
40.5-40.9 45.6-46 |
38-40.4 46.1-48 |
<38 >48 |
| Girdle Thikness, % Word description and percentages |
Thin, Medium, Slightly thick 1.7-3 |
Slightly thin to slightly thick 1.5-4.5 |
Thin to slightly thick 1-4.5 |
Thin to thick 1-5.5 |
Very thin to very thick 0.4-7 |
Extra thin to extra thick 0-7 |
|||
| Total Depth, % Determined by factors already considered above |
58.7-62.3 | 58.7-62.3 | 58.3-58.69 62.31-62.99 |
57.9-58.29 63-63.5 |
57.5-57.89 63.51-63.8 |
57-57.46 63.81-64.1 |
56.5-56.99 64.11-65 |
55-56.49 65.1-67 |
<55 >67 |
| Polish/Symmetry | Excellent | Excellent or Very Good | Excellent to Good | Good or Fair | Poor | ||||
