Metal Gauge to Thickness Chart: Sheet Steel, Stainless, and Aluminum

Gauge numbers are not a universal measurement. Sheet steel, stainless, and aluminum each use a different gauge system, so 16 gauge means three different thicknesses depending on which metal is in front of you. Steel and galvanized run on the Manufacturers Standard Gauge, stainless runs on its own gauge, and aluminum runs on the American Wire Gauge, also called Brown and Sharpe.

Higher gauge numbers mean thinner metal. The values below are nominal. Mill tolerance shifts real stock a few thousandths either way, so measure critical material with calipers before you set your machine. Use the tables to convert a gauge number to decimal inches and millimeters, then carry that thickness into your settings.

Steel Gauge to Thickness (Manufacturers Standard Gauge)

This is the chart for bare mild steel and carbon steel sheet, the most common material in a general fab shop. It follows the Manufacturers Standard Gauge for sheet steel.

A handy reference point: 11 gauge is right at 1/8 inch (0.125 inch nominal is 0.1196 in 11 gauge), 16 gauge is roughly 1/16 inch, and 7 gauge is just under 3/16 inch. Above 7 gauge, steel is normally sold as plate by the fraction (3/16, 1/4, 3/8) rather than by gauge.

Galvanized Steel Gauge to Thickness

Galvanized sheet uses the same gauge numbers as bare steel, but the published thickness includes the zinc coating. That makes a galvanized sheet read a few thousandths thicker than bare steel at the same gauge. The base steel underneath is essentially the same thickness.

When you order duct stock or coated sheet, confirm whether the supplier is quoting base-metal gauge or coated thickness. The two differ by the zinc layer. For welding, the bigger issue with galvanized is the coating itself, not the thickness. The zinc burns off and gives off fume that causes metal fume fever, so it has to be removed back from the joint and the work needs good ventilation. The full picture is in the guide to welding galvanized steel safely.

Stainless Steel Gauge to Thickness

Stainless uses its own gauge system, which does not line up with the steel chart. At a given gauge number, stainless is usually a bit thicker than mild steel. Note that 18 gauge stainless at 0.050 inch is a common kitchen and food-grade thickness.

Stainless suppliers do not all publish identical numbers. Some older tables list 18 gauge stainless at 0.0480 inch instead of 0.050. The differences are small, but if a drawing calls out stainless by gauge for a fit or a flange, get the decimal thickness from the mill cert rather than assuming. Stainless also holds heat differently than mild steel because it conducts heat poorly, so the same gauge runs hotter and warps more under the torch than carbon steel does.

Aluminum Gauge to Thickness (Brown and Sharpe / AWG)

Aluminum sheet thickness follows the American Wire Gauge, also called Brown and Sharpe. This is a different progression again, and aluminum is thinner than steel at the same gauge number. In practice, a lot of aluminum is sold by decimal thickness (0.063, 0.090, 0.125) rather than by gauge, but the gauge callout still shows up.

Why Each Metal Has Its Own Gauge

The gauge systems are leftovers from how sheet and wire were drawn down through dies. Steel settled on the Manufacturers Standard Gauge, which ties a gauge number to a sheet weight (41.82 pounds per square foot for each inch of thickness) rather than to a measured dimension. Aluminum, copper, and brass followed the wire-drawing world and use the American Wire Gauge. Stainless ended up on yet another table. There is no conversion formula between them, which is why a single chart for all three would be wrong. You match the metal first, then read the number.

The practical takeaway: never carry a gauge number across materials. If a drawing says 14 gauge and you switch from steel to aluminum to make the part lighter, you are not making the same thickness. 14 gauge steel is 0.0747 inch and 14 gauge aluminum is 0.0641 inch. That difference changes your weld settings and can change whether the part is strong enough.

Using Gauge Numbers to Pick Weld Settings

Once you have the decimal thickness, the gauge number gets you to a starting point for amperage, voltage, and wire speed. The settings charts on this site are organized by thickness, so the gauge chart is the bridge.

For MIG on mild steel, convert the gauge to decimal inches, find that thickness in the MIG welding settings chart, and start at the low end of the listed range. For TIG, especially on stainless and aluminum where heat control matters more, the TIG welding settings chart is organized the same way. Both assume you will run a test bead on scrap of the same thickness and material before you touch the real part.

Anything in the 24 to 16 gauge range is thin sheet, where burn-through is the main enemy and the gauge difference between materials really shows up. The techniques for that work, including skip welding, backing bars, and pulse settings, are in the guide to welding thin sheet metal.

A Note on Tolerance

Every value in these tables is nominal. Sheet is rolled to a thickness tolerance, so the actual material varies within a band around the chart number. For most fabrication and weld setup the nominal value is close enough to dial in your machine. For anything that has to fit a tolerance, mate to a machined part, or get nested for laser or plasma cutting, measure the actual sheet with calipers or a micrometer. The gauge number tells you what you ordered. The calipers tell you what you got.