Engineering Reference
Sheet Metal Gauge to mm / inch
Quick conversion from gauge number to actual thickness in millimeters and inches, across steel, galvanized, aluminum, and stainless. Used by fabricators, sheet metal shops, and anyone designing parts in CAD that get laser-cut.
Quick mental model
- Lower gauge = thicker metal. 12-gauge is stiffer than 18-gauge.
- Steel uses Manufacturers' Standard; aluminum uses Brown & Sharpe. Same gauge number ≠ same thickness across materials.
- Common rule of thumb: 16-gauge ≈ 1.5 mm, 18-gauge ≈ 1.2 mm, 20-gauge ≈ 0.9 mm (steel).
Gauge thickness chart
| Gauge | Steel | Galvanized | Aluminum | Stainless | ||||
|---|---|---|---|---|---|---|---|---|
| mm | in | mm | in | mm | in | mm | in | |
| 3 | 6.07 | 0.2391 | — | — | 5.83 | 0.2294 | 6.07 | 0.2391 |
| 4 | 5.69 | 0.2242 | — | — | 5.19 | 0.2043 | 5.69 | 0.2242 |
| 5 | 5.31 | 0.2092 | — | — | 4.62 | 0.1819 | 5.31 | 0.2092 |
| 6 | 4.94 | 0.1943 | — | — | 4.11 | 0.1620 | 4.94 | 0.1943 |
| 7 | 4.55 | 0.1793 | — | — | 3.67 | 0.1443 | 4.76 | 0.1875 |
| 8 | 4.18 | 0.1644 | 4.27 | 0.1681 | 3.26 | 0.1285 | 4.37 | 0.1719 |
| 9 | 3.80 | 0.1495 | 3.89 | 0.1532 | 2.91 | 0.1144 | 3.97 | 0.1563 |
| 10 | 3.42 | 0.1345 | 3.51 | 0.1382 | 2.59 | 0.1019 | 3.57 | 0.1406 |
| 11 | 3.04 | 0.1196 | 3.12 | 0.1233 | 2.30 | 0.0907 | 3.18 | 0.1250 |
| 12 | 2.66 | 0.1046 | 2.75 | 0.1084 | 2.05 | 0.0808 | 2.78 | 0.1094 |
| 13 | 2.28 | 0.0897 | 2.37 | 0.0934 | 1.83 | 0.0720 | 2.38 | 0.0938 |
| 14 | 1.90 | 0.0747 | 1.99 | 0.0785 | 1.63 | 0.0641 | 1.98 | 0.0781 |
| 15 | 1.71 | 0.0673 | 1.80 | 0.0710 | 1.45 | 0.0571 | 1.79 | 0.0703 |
| 16 | 1.52 | 0.0598 | 1.61 | 0.0635 | 1.29 | 0.0508 | 1.59 | 0.0625 |
| 17 | 1.37 | 0.0538 | 1.46 | 0.0575 | 1.15 | 0.0453 | 1.43 | 0.0563 |
| 18 | 1.21 | 0.0478 | 1.31 | 0.0516 | 1.02 | 0.0403 | 1.27 | 0.0500 |
| 19 | 1.06 | 0.0418 | 1.15 | 0.0456 | 0.91 | 0.0359 | 1.11 | 0.0438 |
| 20 | 0.91 | 0.0359 | 1.01 | 0.0396 | 0.81 | 0.0320 | 0.95 | 0.0375 |
| 21 | 0.84 | 0.0329 | 0.93 | 0.0366 | 0.72 | 0.0285 | 0.87 | 0.0344 |
| 22 | 0.76 | 0.0299 | 0.85 | 0.0336 | 0.64 | 0.0253 | 0.79 | 0.0313 |
| 23 | 0.68 | 0.0269 | 0.77 | 0.0306 | 0.57 | 0.0226 | 0.71 | 0.0281 |
| 24 | 0.60 | 0.0239 | 0.70 | 0.0276 | 0.51 | 0.0201 | 0.64 | 0.0250 |
| 25 | 0.53 | 0.0209 | 0.62 | 0.0247 | 0.45 | 0.0179 | 0.56 | 0.0219 |
| 26 | 0.45 | 0.0179 | 0.55 | 0.0217 | 0.40 | 0.0159 | 0.48 | 0.0188 |
| 27 | 0.42 | 0.0164 | 0.51 | 0.0202 | 0.36 | 0.0142 | 0.44 | 0.0172 |
| 28 | 0.38 | 0.0149 | 0.47 | 0.0187 | 0.32 | 0.0126 | 0.41 | 0.0156 |
| 29 | 0.34 | 0.0135 | 0.44 | 0.0172 | 0.29 | 0.0113 | 0.36 | 0.0141 |
| 30 | 0.30 | 0.0120 | 0.40 | 0.0157 | 0.25 | 0.0100 | 0.32 | 0.0125 |
Steel and galvanized use Manufacturers' Standard Gauge. Aluminum uses Brown & Sharpe (B&S) Gauge. Stainless approximates US Standard Gauge converted to sheet practice. Values rounded to 2 decimals (mm) or 4 decimals (inches).
Common applications by thickness
| Gauge range | Thickness | Typical uses |
|---|---|---|
| 10-12 | 2.5-3.5 mm | Industrial enclosures, heavy-duty brackets, structural panels |
| 14-16 | 1.5-2.0 mm | HVAC ducting (commercial), automotive body panels, kitchen sinks |
| 18-20 | 1.0-1.2 mm | HVAC (residential), appliance casings, general fabrication |
| 22-24 | 0.6-0.8 mm | Roof flashing, decorative panels, light kitchenware |
| 26-28 | 0.4-0.5 mm | Stovepipes, light-duty enclosures, thin shielding |
FAQ
Why does the gauge number get bigger as the metal gets thinner?
Historical accident from the wire-drawing industry. Higher gauge meant more passes through the drawing die, which produced thinner wire. The convention stuck, even though it's confusing to anyone who didn't grow up with it.
Are aluminum and steel gauges the same thickness?
No. Aluminum uses the Brown & Sharpe (B&S) gauge system, which is different from the Manufacturers' Standard used for steel. 18-gauge steel is about 1.21 mm, but 18-gauge aluminum is about 1.02 mm. Always check the material when reading gauge specs.
What gauge is 1 mm aluminum?
Roughly 18-gauge in the B&S system (1.02 mm). 1 mm aluminum is a common stock thickness for sheet-metal projects.
Is 16-gauge stronger than 14-gauge?
No — 14-gauge is thicker, therefore stronger. Lower gauge number = thicker metal = more stiffness and load-bearing capacity. The same applies to stud framing, where 16-gauge studs are noticeably thinner than 14-gauge.
What's the standard ductwork gauge?
Residential HVAC supply ducts are typically 26-30 gauge. Commercial supply ducts step up to 24-26 gauge. Plenums and large-volume ducts use 22 gauge or heavier. SMACNA tables are the authoritative source.
Can I 3D print a part to replace sheet metal?
For prototypes and low-stress parts, yes — 2-3 mm wall thickness in PETG or ABS roughly approximates 12-14 gauge stiffness. For structural or thermal applications, sheet metal still wins.