Here’s a clean SWG table from 16 down to 30. Diameters shown in inches and millimetres.
| SWG | Inches | mm |
| 16 | 0.0640″ | 1.626 mm |
| 17 | 0.0560″ | 1.422 mm |
| 18 | 0.0480″ | 1.219 mm |
| 19 | 0.0400″ | 1.016 mm |
| 20 | 0.0360″ | 0.914 mm |
| 21 | 0.0320″ | 0.813 mm |
| 22 | 0.0280″ | 0.711 mm |
| 23 | 0.0240″ | 0.610 mm |
| 24 | 0.0220″ | 0.559 mm |
| 25 | 0.0200″ | 0.508 mm |
| 26 | 0.0180″ | 0.457 mm |
| 27 | 0.0164″ | 0.417 mm |
| 28 | 0.0148″ | 0.376 mm |
| 29 | 0.0136″ | 0.345 mm |
| 30 | 0.0124″ | 0.315 mm |