Understanding Gauges and Equivalent Thicknesses in Sheet Metal

As you may have noticed, we measure sheet metal’s thickness by its ‘gauge’, simply measuring its thickness. Why not use millimetres or even fractions of an inch? On one level, it is tradition, but it is because everyone else in the industry uses the gauge system. We want our products to be compatible with all the machinery and processes our customers will likely use.

The steel wire industry invented the ’gauge’ system, but it soon became applied to all types of metal production. The wire was produced by drawing iron through smaller and smaller holes in a hard piece of metal. This had to be done incrementally –first draw wire through the #1 hole (producing 1ga wire), then through the #2 hole (thinner 2ga wire), etc. That’s why higher gauge numbers mean thinner metal products.

Now, one would think that would be confusing enough. One would be wrong.

To make it less transparent, several different ‘gauge’ values are used for different types of metal. Why? Because softer metals like copper or brass could be drawn through different-sized holes than iron or steel. So today, ‘37ga steel sheeting’ (or 37 ga steel wire) is a slightly different thickness than ‘37 ga aluminium sheeting’ or ‘16 ga copper sheeting’.

For the record, 7 ga stainless steel is 0.0066 inches thick, whereas 7 ga aluminium is only 0.0045 inches thick.

Here is the table for aluminium and how each ‘gauge’ measures out in mm and inches. Wikipedia provide a full chart for different types of metal.

Complicated enough? Of course not!

• In the 19^th century, all gauge measures in England were standardised to exact fractions of an inch. Only… not all manufacturers used the new standards, as that would have meant expensive retooling.
• Later, the Standard Wire Gauge was adopted across the UK. It was… not universally used.
• In the 20^th century, a new gauge standard was supposed to be introduced based on metric units. It… just never actually happened.
• In the 21^st century, different segments of different industries use entirely different definitions for ‘gauge’ in other contexts, and it looks like that’s just the way it will stay.

So, how does one actually measure something .01 mm thick, or meaningfully distinguish it from sheeting that is .0113 or .0089mm thick?

Indeed fabricators aren’t whipping out an electron microscope, the world’s tiniest tape measure, and a vast jeweller’s loupe in the shop?

Measuring a wire gauge, a sheet of metal, or any other metal part is a lot like gapping a spark plug. You need a unique tool.

Enter the gauge wheel. A gauge wheel is usually a metal disk with a series of up to 50 very precisely machined slots cut in its edge. Next to each is a number – the gauge of a piece of metal that will barely fit into that gap but not into the next smaller gap.

If you’re not sure what gauge of sheeting you need – talk to our experts, they can suggest the exact material that will be best suited to your intended purpose, price range and other factors.