Why does the same gauge mean different thicknesses for different metals?

Gauge is a historical wire-and-sheet numbering system, not a unit. Steel and stainless follow the Manufacturers' Standard Gauge, while aluminium, copper, and brass follow the Brown and Sharpe gauge. The same gauge number therefore corresponds to a different physical thickness in each metal.

Does a higher gauge number mean thicker or thinner metal?

Thinner. The gauge scale runs backwards, so a higher number is a thinner sheet. For example, 26 gauge steel is much thinner than 14 gauge steel. This is the opposite of what many people expect.

Why is galvanised steel thicker than plain steel at the same gauge?

Galvanised steel starts as standard steel and then receives a zinc coating. The gauge tables add a small allowance for that coating, so a galvanised sheet measures slightly thicker than a bare steel sheet of the same gauge number.

How do I convert gauge to millimetres?

First find the thickness in inches from the table for your material, then multiply by 25.4 to get millimetres. The tool does this automatically and also shows mils, which are thousandths of an inch, for coating and tolerance work.

Is stainless the same gauge as carbon steel?

Stainless sheet thicknesses are based on the carbon-steel standard gauge with slightly rounded values. They are close to plain steel but not identical, which is why stainless has its own column in the table.

Sheet Metal Gauge Reference

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A gauge number is not a measurement — it is an index into a lookup table, and the table differs by metal. This reference converts gauge numbers into real thickness in inches, millimetres, and mils for the five most common sheet materials.

How it works

Two main gauge systems are in use. Steel and stainless follow the Manufacturers’ Standard Gauge, where galvanised steel adds a thin zinc-coating allowance on top of the bare-steel value. Aluminium, copper, and brass follow the Brown & Sharpe (B&S, also called AWG) gauge, which produces entirely different thicknesses for the same number.

The scale is counter-intuitive in two ways: the number runs backwards (higher gauge = thinner sheet), and the steps are roughly geometric rather than linear. Once the thickness in inches is known, the metric value is a simple unit conversion:

mm   = inch × 25.4
mils = inch × 1000

The tool stores the published nominal inch thickness for each gauge and material and derives the mm and mils columns from it.

Example and notes

A common fabrication question is “how thick is 16 gauge?” — and the honest answer is “of what?” 16 gauge standard steel is 0.0598 in (1.52 mm), 16 gauge galvanised steel is 0.0635 in (1.61 mm), but 16 gauge aluminium is only 0.0508 in (1.29 mm). Always state the material with the gauge.

Real sheet carries a thickness tolerance, so order against a thickness spec for precision parts rather than a gauge number alone. When a drawing gives only a gauge, confirm which gauge system the supplier uses before cutting tooling.