Birmingham Wire Gauge is dimensional gauge for wire, it also specifies wall thickness or diameter of steel tube, the gauge numbers range from 1 to 30, each number represents a value for tube wall thickness, and corresponding to convert inches and millimeters as table below, low BWG number correspond to large size, opposite, high BWG number mean small size.
Birmingham Wire Gauge (BWG) Chart
| BWG | in | mm |
|---|---|---|
| 1 | 0.3 | 7.62 |
| 2 | 0.283 | 7.21 |
| 3 | 0.259 | 6.58 |
| 4 | 0.238 | 6.05 |
| 5 | 0.22 | 5.59 |
| 6 | 0.203 | 5.16 |
| 7 | 0.179 | 4.57 |
| 8 | 0.164 | 4.19 |
| 9 | 0.147 | 3.76 |
| 10 | 0.134 | 3.4 |
| 11 | 0.12 | 3.05 |
| 12 | 0.109 | 2.77 |
| 13 | 0.095 | 2.41 |
| 14 | 0.083 | 2.11 |
| 15 | 0.072 | 1.83 |
| 16 | 0.065 | 1.65 |
| 17 | 0.058 | 1.47 |
| 18 | 0.049 | 1.24 |
| 19 | 0.042 | 1.07 |
| 20 | 0.035 | 0.89 |
| 21 | 0.031 | 0.81 |
| 22 | 0.028 | 0.71 |
| 23 | 0.025 | 0.64 |
| 24 | 0.023 | 0.56 |
| 25 | 0.02 | 0.51 |
| 26 | 0.018 | 0.46 |
| 27 | 0.016 | 0.41 |
| 28 | 0.0135 | 0.356 |
| 29 | 0.013 | 0.33 |
| 30 | 0.012 | 0.305 |
| 31 | 0.01 | 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 |
For stainless steel tube, BWG Gauge is commonly used to define wall thickness, for example, BWG 16 indicates 1.65 mm wall thickness of tube, 18 BWG is 1.24 mm wall, and the outside diameter of tubes is the actual outside diameter in inches or millimeters.