BWG is short for Birmingham Wire Gauge. It is a wire gauge system. Since nails are manufactured from steel wires, BWG is the perfect system to evaluate nail wire thickness.
Besides wires, BWG is also used to specify the thickness or diameter of needles and tube products.
Gauge System For Nail Wire
Concerning nails, the gauge number is used to specify the outside diameter of the wire.
- Lowest gauge number is 5/0, equals to largest thickness 0.500 inch (12.7mm)
- Largest gauge number is 36, equals to smallest thickness 0.004 inch (0.102mm)
The common size for umbrella head roofing nails is BWG9*2.5″. Meaning the wire thickness is BWG9 = 0.148 inches = 3.759mm. (According to conversion in Chart 1 below).
Conversion Table
Covert BWG to inches and mm. Very useful to convert wire nail gauge into milimeter.
| BWG | inches | mm |
| (5/0) | 0.500 | 12.7 |
| (4/0) | 0.454 | 11.532 |
| (3/0) | 0.425 | 10.795 |
| (2/0) | 0.380 | 9.652 |
| 0 | 0.340 | 8.636 |
| 1 | 0.300 | 7.62 |
| 2 | 0.284 | 7.213 |
| 3 | 0.259 | 6.579 |
| 4 | 0.238 | 6.045 |
| 5 | 0.220 | 5.588 |
| 6 | 0.203 | 5.156 |
| 7 | 0.180 | 4.572 |
| 8 | 0.165 | 4.191 |
| 9 | 0.148 | 3.759 |
| 10 | 0.134 | 3.404 |
| 11 | 0.120 | 3.048 |
| 12 | 0.109 | 2.769 |
| 13 | 0.095 | 2.413 |
| 14 | 0.083 | 2.108 |
| 15 | 0.072 | 1.829 |
| 16 | 0.065 | 1.651 |
| 17 | 0.058 | 1.473 |
| 18 | 0.049 | 1.245 |
| 19 | 0.042 | 1.067 |
| 20 | 0.035 | 0.888 |
| 21 | 0.032 | 0.813 |
| 22 | 0.028 | 0.711 |
| 23 | 0.025 | 0.635 |
| 24 | 0.022 | 0.559 |
| 25 | 0.020 | 0.508 |
| 26 | 0.018 | 0.457 |
| 27 | 0.016 | 0.406 |
| 28 | 0.014 | 0.356 |
| 29 | 0.013 | 0.330 |
| 30 | 0.012 | 0.305 |
| 31 | 0.010 | 0.254 |
| 32 | 0.009 | 0.229 |
| 33 | 0.008 | 0.203 |
| 34 | 0.007 | 0.178 |
| 35 | 0.005 | 0.127 |
| 36 | 0.004 | 0.102 |
