Reference
Sheet Metal Gauge Chart
Gauge to thickness for the four materials shops actually stock, in inches and millimeters, plus why the same gauge number means four different thicknesses.
Sheet metal gauge is a legacy numbering system where a higher number means a thinner sheet. It is not a unit, and it is not consistent between materials: 16 gauge steel is 0.0598 inch, 16 gauge stainless is 0.0625 inch, and 16 gauge aluminum is 0.0508 inch. Those are three different sheets. Use this chart to convert, then put the decimal thickness on your drawing rather than the gauge number.
Gauge to thickness, by material
Steel follows the Manufacturers' Standard Gauge. Galvanized steel uses the same base but adds the zinc coating, so it measures slightly thicker at the same gauge. Stainless has its own standard. Aluminum follows the Brown & Sharpe (American Wire Gauge) system, which is why it is the furthest from the others.
| Gauge | Steel | Galvanized steel | Stainless steel | Aluminum |
|---|---|---|---|---|
| 7 | 0.1793 in (4.55 mm) | not standard | 0.1875 in (4.76 mm) | 0.1443 in (3.67 mm) |
| 8 | 0.1644 in (4.18 mm) | 0.1681 in (4.27 mm) | 0.1719 in (4.37 mm) | 0.1285 in (3.26 mm) |
| 10 | 0.1345 in (3.42 mm) | 0.1382 in (3.51 mm) | 0.1406 in (3.57 mm) | 0.1019 in (2.59 mm) |
| 11 | 0.1196 in (3.04 mm) | 0.1233 in (3.13 mm) | 0.1250 in (3.17 mm) | 0.0907 in (2.30 mm) |
| 12 | 0.1046 in (2.66 mm) | 0.1084 in (2.75 mm) | 0.1094 in (2.78 mm) | 0.0808 in (2.05 mm) |
| 14 | 0.0747 in (1.90 mm) | 0.0785 in (1.99 mm) | 0.0781 in (1.98 mm) | 0.0641 in (1.63 mm) |
| 16 | 0.0598 in (1.52 mm) | 0.0635 in (1.61 mm) | 0.0625 in (1.59 mm) | 0.0508 in (1.29 mm) |
| 18 | 0.0478 in (1.21 mm) | 0.0516 in (1.31 mm) | 0.0500 in (1.27 mm) | 0.0403 in (1.02 mm) |
| 20 | 0.0359 in (0.91 mm) | 0.0396 in (1.01 mm) | 0.0375 in (0.95 mm) | 0.0320 in (0.81 mm) |
| 22 | 0.0299 in (0.76 mm) | 0.0336 in (0.85 mm) | 0.0312 in (0.79 mm) | 0.0253 in (0.64 mm) |
| 24 | 0.0239 in (0.61 mm) | 0.0276 in (0.70 mm) | 0.0250 in (0.64 mm) | 0.0201 in (0.51 mm) |
| 26 | 0.0179 in (0.45 mm) | 0.0217 in (0.55 mm) | 0.0187 in (0.47 mm) | 0.0159 in (0.40 mm) |
Nominal thicknesses. Mill tolerance applies on top, so an actual sheet will measure slightly over or under.
Why one gauge number is four thicknesses
The system predates decimal measurement and grew out of separate trades. Steel gauge came from the weight of a sheet per square foot, stainless was standardized separately, and aluminum inherited a wire gauge scale. Nothing reconciled them.
The practical consequence is that a drawing calling for '16 gauge' without naming the material is ambiguous by up to 0.012 inch, which is more than a fifth of the sheet thickness. On a folded enclosure that is enough to change the fit of a lid, the engagement of a self-clinching fastener, and the achievable bend radius.
Galvanized is the trap inside the trap: the gauge refers to the base steel, but you receive base steel plus zinc. At 20 gauge that is about 0.0037 inch of extra material, and it lands on every surface including the inside of a bend.
What shops actually stock
Availability is narrower than the chart suggests, and ordering an unstocked thickness adds lead time even when the price looks fine.
The reliable stock thicknesses for prototype and low volume work are 20, 18, 16, 14 and 11 gauge in steel and stainless, and 0.040, 0.050, 0.063, 0.080, 0.090 and 0.125 inch in aluminum. Aluminum is commonly ordered by decimal thickness rather than by gauge, and specifying it that way avoids the conversion entirely.
If your design tolerates it, snap to those thicknesses. Moving from an unusual gauge to the next stocked one is one of the cheapest changes available on a sheet metal part.
| Application | Typical gauge | Thickness |
|---|---|---|
| Electronics enclosure, light bracket | 20 ga steel | 0.0359 in (0.91 mm) |
| General enclosure, chassis panel | 18 ga steel | 0.0478 in (1.21 mm) |
| Structural bracket, machine guard | 16 ga steel | 0.0598 in (1.52 mm) |
| Load bearing bracket, base plate | 14 ga steel | 0.0747 in (1.90 mm) |
| Heavy frame, weldment | 11 ga steel | 0.1196 in (3.04 mm) |
| Sheet aluminum enclosure | 0.063 in nominal | 1.60 mm |
| Aluminum structural panel | 0.125 in nominal | 3.18 mm |
Thickness tolerance, and why your part measures off
The chart gives nominal values. Mills ship to a thickness tolerance, and for thin sheet that tolerance is a meaningful fraction of the material.
On 20 gauge steel a typical mill tolerance is around plus or minus 0.003 inch, roughly 8 percent of the sheet. If your design stacks several folded walls, or presses a bearing into a formed feature, that variation accumulates the same way any other tolerance does.
This is why a sheet metal part that measures correct on the flat pattern can still come out wrong on the assembly, and why critical dimensions on formed parts should be called out on the feature that matters rather than derived from nominal thickness.
How to specify it so nothing gets lost
State the decimal thickness first and the gauge second, if at all: '0.0598 in (16 ga) CRS'. That way the number survives even if the material changes.
Name the material and the finish, because galvanized and painted stock arrive thicker than bare. Say whether the thickness is critical or nominal. And on any formed feature with a fit, dimension the finished feature rather than trusting the flat pattern to land.
A shop that receives a decimal thickness and a named alloy never has to guess which gauge table you were reading.
Gauge is a legacy scale, not a unit. Put the decimal thickness on the drawing and the gauge number in parentheses if you want it at all.