ASTM grain size
The equivalent, G, ASTM grain size number can be calculated from, L, the mean intercept length as; G = - 3.2877 - 6.6439 log_10{L}, where L is given in mm.
| ASTM Grain size number | Mean Intercept grain size (Micrometer) |
| -2 | 640.0 |
| -1.5 | 538.2 |
| -1 | 452.6 |
| -0.5 | 380.6 |
| 0 | 320.0 |
| 0.5 | 269.1 |
| 1 | 226.3 |
| 1.5 | 190.3 |
| 2 | 160.0 |
| 2.5 | 134.5 |
| 3 | 113.1 |
| 3.5 | 95.1 |
| 4 | 80.0 |
| 4.5 | 67.3 |
| 5 | 56.6 |
| 5.5 | 47.6 |
| 6 | 40.0 |
| 6.5 | 33.6 |
| 7 | 28.3 |
| 7.5 | 23.8 |
| 8 | 20.0 |
| 8.5 | 16.8 |
| 9 | 14.1 |
| 9.5 | 11.9 |
| 10 | 10.0 |
| 10.5 | 8.41 |
| 11 | 7.07 |
| 11.5 | 5.95 |
| 12 | 5.00 |
| 12.5 | 4.20 |
| 13 | 3.54 |
| 13.5 | 2.97 |
| 14 | 2.50 |
| 14.5 | 2.10 |
| 15 | 1.77 |
| 15.5 | 1.49 |
| 16 | 1.25 |
| 16.5 | 1.05 |
| 17 | 0.88 |
| 17.5 | 0.74 |
| 18 | 0.63 |
| 18.5 | 0.53 |
| 19 | 0.44 |
| 19.5 | 0.37 |