Sheet metal is one of the few materials where the numbering system works backwards: the higher the gauge, the thinner the metal. It catches people out constantly, and ordering the wrong one is an expensive mistake.
Why Higher Gauge Means Thinner Metal
The system dates back to wire drawing, where the number counted how many times the metal was pulled through a die to reduce it. More passes meant thinner wire and a higher number. The convention stuck for sheet, so 16 gauge is noticeably thicker than 22 gauge.
This is also why gauge is gradually being replaced by a straightforward millimetre measurement, which removes the ambiguity entirely.
The Same Gauge Is Not the Same Thickness
Here is the part that causes real errors: gauge is material-specific. A given gauge in mild steel, stainless steel and aluminium are three different thicknesses, because the systems developed separately for each metal.
Specifying in millimetres avoids the problem completely. When in doubt, state the thickness you actually want rather than a gauge number.
Choosing Thickness for the Job
Thin sheet is lighter, cheaper and easier to form, but it dents, flexes and distorts more readily under welding heat. Thick sheet is rigid and durable but harder to bend and heavier to handle and mount.
Most decisions come down to whether the panel is structural or cosmetic. A cover or cladding panel can be thin. A bracket carrying load, or a panel that will be knocked, should not be.
Thickness and Welding
Thin sheet is far harder to weld than thick. There is very little material to absorb the heat, so it burns through easily and distorts as it cools. This is why thin sheet work is usually TIG welded or joined by other means – the control is worth the extra time. See TIG vs arc welding for how the processes compare.
Bending Thickness
Every bend needs a minimum internal radius relative to the material thickness, and bending tighter than the material allows cracks the outside of the bend. Aluminium is less forgiving here than mild steel, particularly in harder alloys.
See sheet metal bending and shaping for what we can form, and mild steel fabrication for general sheet and section work.
Frequently Asked Questions
Is 16 gauge thicker than 20 gauge?
Yes. The gauge scale runs backwards – lower numbers are thicker. 16 gauge steel is roughly 1.6mm while 20 gauge is around 0.9mm, so the difference is substantial.
Why does the same gauge differ between steel and aluminium?
The gauge systems developed independently for different metals, so the same number refers to different thicknesses depending on the material. Specifying in millimetres removes the confusion.
What thickness should I use for a bracket that carries weight?
That depends on the load, the span and how it is fixed rather than on a single rule. As a starting point, structural brackets are usually made from plate or flat bar rather than thin sheet, because sheet flexes under sustained load.
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