Sheet metal gauge chart
Gauge number to thickness in millimetres and inches. Mild steel, stainless and aluminium each use a different scale, so the same gauge number is three different thicknesses — all three are side by side below.
Full conversion table
| Gauge | Mild steel | Stainless | Aluminium |
|---|---|---|---|
| 7 | 4.55 mm | 4.76 mm | 3.67 mm |
| 8 | 4.18 mm | 4.37 mm | 3.26 mm |
| 9 | 3.80 mm | 3.97 mm | 2.91 mm |
| 10 | 3.42 mm | 3.57 mm | 2.59 mm |
| 11 | 3.04 mm | 3.17 mm | 2.30 mm |
| 12 | 2.66 mm | 2.78 mm | 2.05 mm |
| 13 | 2.28 mm | 2.38 mm | 1.83 mm |
| 14 | 1.90 mm | 1.98 mm | 1.63 mm |
| 15 | 1.71 mm | 1.79 mm | 1.45 mm |
| 16 | 1.52 mm | 1.59 mm | 1.29 mm |
| 17 | 1.37 mm | 1.43 mm | 1.15 mm |
| 18 | 1.21 mm | 1.27 mm | 1.02 mm |
| 19 | 1.06 mm | 1.11 mm | 0.91 mm |
| 20 | 0.91 mm | 0.95 mm | 0.81 mm |
| 21 | 0.84 mm | 0.87 mm | 0.72 mm |
| 22 | 0.76 mm | 0.80 mm | 0.64 mm |
| 24 | 0.61 mm | 0.64 mm | 0.51 mm |
| 26 | 0.45 mm | 0.48 mm | 0.40 mm |
| 28 | 0.38 mm | 0.40 mm | 0.32 mm |
Nominal values. Real sheet carries a rolling tolerance, and suppliers outside North America often stock metric thicknesses (1.0, 1.5, 2.0, 3.0 mm) that do not map onto a gauge number at all.
Why the exact thickness matters
Thickness feeds directly into every bend calculation. The bend allowance formula multiplies the K-factor by the thickness to locate the neutral axis, and the outside setback adds the thickness to the inside radius. Assume 1.5 mm when the sheet is actually 1.52 mm and every flange on a multi-bend part drifts.
It matters for the bend itself too. The minimum inside radius a material tolerates without cracking scales with thickness, and a hole placed closer than about 2.5 times the thickness to a bend line will distort when it folds. Coobic flags both while you draw.
So: order by gauge if that is how your supplier sells it, but put the millimetre value on the drawing and into your CAD.
Frequently asked questions
How thick is 16 gauge steel in mm?
16 gauge mild steel is 0.0598 inches, which is 1.52 mm. In stainless steel the same gauge number is 1.59 mm, and in aluminium it is 1.29 mm.
Why does a gauge number mean different thicknesses in different metals?
Gauge scales were developed separately for different materials and were never unified. Mild steel uses the Manufacturers Standard Gauge, stainless has its own steel-plate scale, and aluminium uses the Brown & Sharpe scale. The same number gives three different thicknesses.
Does a higher gauge number mean thicker metal?
No, the opposite. Gauge numbers run backwards: the higher the number, the thinner the sheet. 28 gauge is thin foil-like sheet, 7 gauge is heavy plate.
Should I specify gauge or millimetres on a drawing?
Specify millimetres. Gauge is ambiguous across materials and suppliers, and every bend calculation depends on the actual thickness. Give the millimetre value and name the material and gauge only as a cross-check.
Design a part in this thickness
Set the thickness in millimetres, draw the flat pattern, add bends, and export a DXF ready for the laser.
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