Reference
Sheet Metal Gauge Chart
Gauge to thickness from 3 to 30 gauge for the four materials shops stock, in inches and millimeters, plus steel weight per square foot and 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.
Quick answers (steel): 10 gauge is 0.1345 in (3.42 mm). 11 gauge is 0.1196 in (3.04 mm). 12 gauge is 0.1046 in (2.66 mm). 14 gauge is 0.0747 in (1.90 mm). 16 gauge is 0.0598 in (1.52 mm). 18 gauge is 0.0478 in (1.21 mm). 20 gauge is 0.0359 in (0.91 mm).
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 |
|---|---|---|---|---|
| 3 | 0.2391 in (6.07 mm) | not standard | 0.2500 in (6.35 mm) | 0.2294 in (5.83 mm) |
| 4 | 0.2242 in (5.69 mm) | not standard | 0.2344 in (5.95 mm) | 0.2043 in (5.19 mm) |
| 5 | 0.2092 in (5.31 mm) | not standard | 0.2188 in (5.56 mm) | 0.1819 in (4.62 mm) |
| 6 | 0.1943 in (4.94 mm) | not standard | 0.2031 in (5.16 mm) | 0.1620 in (4.11 mm) |
| 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) |
| 9 | 0.1495 in (3.80 mm) | 0.1532 in (3.89 mm) | 0.1563 in (3.97 mm) | 0.1144 in (2.91 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 (3.18 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) |
| 13 | 0.0897 in (2.28 mm) | 0.0934 in (2.37 mm) | 0.0938 in (2.38 mm) | 0.0720 in (1.83 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) |
| 15 | 0.0673 in (1.71 mm) | 0.0710 in (1.80 mm) | 0.0703 in (1.79 mm) | 0.0571 in (1.45 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) |
| 17 | 0.0538 in (1.37 mm) | 0.0575 in (1.46 mm) | 0.0563 in (1.43 mm) | 0.0453 in (1.15 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) |
| 19 | 0.0418 in (1.06 mm) | 0.0456 in (1.16 mm) | 0.0438 in (1.11 mm) | 0.0359 in (0.91 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) |
| 21 | 0.0329 in (0.84 mm) | 0.0366 in (0.93 mm) | 0.0344 in (0.87 mm) | 0.0285 in (0.72 mm) |
| 22 | 0.0299 in (0.76 mm) | 0.0336 in (0.85 mm) | 0.0313 in (0.80 mm) | 0.0253 in (0.64 mm) |
| 23 | 0.0269 in (0.68 mm) | 0.0306 in (0.78 mm) | 0.0281 in (0.71 mm) | 0.0226 in (0.57 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) |
| 25 | 0.0209 in (0.53 mm) | 0.0247 in (0.63 mm) | 0.0219 in (0.56 mm) | 0.0179 in (0.45 mm) |
| 26 | 0.0179 in (0.45 mm) | 0.0217 in (0.55 mm) | 0.0188 in (0.48 mm) | 0.0159 in (0.40 mm) |
| 27 | 0.0164 in (0.42 mm) | 0.0202 in (0.51 mm) | 0.0172 in (0.44 mm) | 0.0142 in (0.36 mm) |
| 28 | 0.0149 in (0.38 mm) | 0.0187 in (0.47 mm) | 0.0156 in (0.40 mm) | 0.0126 in (0.32 mm) |
| 29 | 0.0135 in (0.34 mm) | 0.0172 in (0.44 mm) | 0.0141 in (0.36 mm) | 0.0113 in (0.29 mm) |
| 30 | 0.0120 in (0.30 mm) | 0.0157 in (0.40 mm) | 0.0125 in (0.32 mm) | 0.0100 in (0.25 mm) |
Nominal thicknesses. Mill tolerance applies on top, so an actual sheet will measure slightly over or under.
Steel gauge thickness, fraction, and weight
Manufacturers' Standard Gauge is defined by weight: 41.82 lb per square foot for every inch of thickness. That makes weight per square foot an exact conversion, useful for estimating part weight and freight. The nearest fraction is for reference only; order and dimension by decimal thickness.
| Gauge | Thickness (in) | Thickness (mm) | Nearest fraction (in) | Weight (lb/ft²) |
|---|---|---|---|---|
| 7 | 0.1793 | 4.55 | 11/64 | 7.50 |
| 8 | 0.1644 | 4.18 | 11/64 | 6.88 |
| 9 | 0.1495 | 3.80 | 5/32 | 6.25 |
| 10 | 0.1345 | 3.42 | 9/64 | 5.62 |
| 11 | 0.1196 | 3.04 | 1/8 | 5.00 |
| 12 | 0.1046 | 2.66 | 7/64 | 4.37 |
| 13 | 0.0897 | 2.28 | 3/32 | 3.75 |
| 14 | 0.0747 | 1.90 | 5/64 | 3.12 |
| 15 | 0.0673 | 1.71 | 1/16 | 2.81 |
| 16 | 0.0598 | 1.52 | 1/16 | 2.50 |
| 17 | 0.0538 | 1.37 | 3/64 | 2.25 |
| 18 | 0.0478 | 1.21 | 3/64 | 2.00 |
| 19 | 0.0418 | 1.06 | 3/64 | 1.75 |
| 20 | 0.0359 | 0.91 | 1/32 | 1.50 |
| 21 | 0.0329 | 0.84 | 1/32 | 1.38 |
| 22 | 0.0299 | 0.76 | 1/32 | 1.25 |
| 23 | 0.0269 | 0.68 | 1/32 | 1.12 |
| 24 | 0.0239 | 0.61 | 1/32 | 1.00 |
| 25 | 0.0209 | 0.53 | 1/64 | 0.87 |
| 26 | 0.0179 | 0.45 | 1/64 | 0.75 |
| 27 | 0.0164 | 0.42 | 1/64 | 0.69 |
| 28 | 0.0149 | 0.38 | 1/64 | 0.62 |
| 29 | 0.0135 | 0.34 | 1/64 | 0.56 |
| 30 | 0.0120 | 0.30 | 1/64 | 0.50 |
Weight is for bare carbon steel at nominal thickness. Galvanized sheet weighs slightly more because of the zinc coating.
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.