Sheet metal gauge chart
These are the four systems you meet in a workshop. Mild steel and galvanised use the Manufacturers Standard Gauge, stainless uses its own, and aluminium uses the Brown and Sharpe system, which is why an aluminium sheet of the same gauge always feels thinner.
Galvanised is the same base steel plus the zinc coating, so a galvanised sheet is slightly thicker than plain steel at the same gauge.
| Gauge | Mild steel | Galvanised | Stainless | Aluminium |
|---|---|---|---|---|
| 7 | 0.1793 (4.55) | - | 0.1875 (4.76) | 0.1443 (3.67) |
| 8 | 0.1644 (4.18) | 0.1681 (4.27) | 0.1719 (4.37) | 0.1285 (3.26) |
| 10 | 0.1345 (3.42) | 0.1382 (3.51) | 0.1406 (3.57) | 0.1019 (2.59) |
| 11 | 0.1196 (3.04) | 0.1233 (3.13) | 0.1250 (3.18) | 0.0907 (2.30) |
| 12 | 0.1046 (2.66) | 0.1084 (2.75) | 0.1094 (2.78) | 0.0808 (2.05) |
| 14 | 0.0747 (1.90) | 0.0785 (1.99) | 0.0781 (1.98) | 0.0641 (1.63) |
| 16 | 0.0598 (1.52) | 0.0635 (1.61) | 0.0625 (1.59) | 0.0508 (1.29) |
| 18 | 0.0478 (1.21) | 0.0516 (1.31) | 0.0500 (1.27) | 0.0403 (1.02) |
| 20 | 0.0359 (0.91) | 0.0396 (1.01) | 0.0375 (0.95) | 0.0320 (0.81) |
| 22 | 0.0299 (0.76) | 0.0336 (0.85) | 0.0313 (0.79) | 0.0253 (0.64) |
| 24 | 0.0239 (0.61) | 0.0276 (0.70) | 0.0250 (0.64) | 0.0201 (0.51) |
| 26 | 0.0179 (0.45) | 0.0217 (0.55) | 0.0188 (0.48) | 0.0159 (0.40) |
Why the gauge numbers run backwards
The system came from wire drawing. A wire was pulled through a die a number of times to reduce it, and the gauge number counted the passes. More passes meant a thinner wire, so a bigger number meant less material. Sheet inherited the same numbering.
That history is also why the number carries no unit and does not convert between materials. Always confirm which material a gauge figure refers to before ordering, and where it matters, specify the thickness in millimetres instead and let the gauge follow.
What each gauge is used for
20 and 22 gauge is ducting and light enclosure work. 18 gauge is the common choice for brackets, guards and general fabrication where the part has to hold shape but still bend on a small brake.
14 and 16 gauge is structural sheet: tool boxes, machine panels, trailer skins. 14 gauge is around the limit for a hand brake in anything wider than a few hundred millimetres.
10 and 12 gauge needs a powered brake and is usually welded rather than folded. At 7 gauge and thicker the material is normally called plate rather than sheet.
