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Gauge table
Standard Wire Gauge (SWG)
The legal British wire scale, and it runs backwards.
Origin
Made a legal standard by the Weights and Measures Act of 1883, superseding the competing Birmingham and Lancashire gauges.
The catch
The higher the number, the thinner the wire. The scale counts how many times the wire was drawn through a die, and each pass made it finer.
| Gauge | Inches | Millimetres | Typical use |
|---|---|---|---|
| 7/0 | 0.500 | 12.70 | Heavy structural wire rope |
| 4/0 | 0.400 | 10.16 | Suspension cable strand |
| 0 | 0.324 | 8.23 | Fencing and heavy springs |
| 8 | 0.160 | 4.06 | Light fencing |
| 16 | 0.064 | 1.63 | Coat hangers, general wire |
| 20 | 0.036 | 0.914 | Picture wire |
| 24 | 0.022 | 0.559 | Electrical windings |
| 30 | 0.0124 | 0.315 | Fine coil winding |
| 40 | 0.0048 | 0.122 | Instrument wire |
| 50 | 0.0010 | 0.0254 | Finer than a human hair |
Before 1883 every manufacturing town kept its own gauge, and a 16-gauge wire from Birmingham was not a 16-gauge wire from Lancashire. The 1883 Act imposed a single legal standard, though the older gauges survived in their trades for decades and the Birmingham Wire Gauge is still quoted for some tubing today.