It appears the American gauge measurement is equally arcane. I am often use the decimal system and metric for high quality steel and other metals.

From Tim Shoppa in CA;

"The earliest standard for sheet metal gauges actually ran the other way. This is the American Institute of Mining Engineers Standard Decimal Gauge, from 1877. The gauge number was the thickness of the sheet in thousandths of an inch. The series ran from 2 to 22 by 2's, 25, 28 to 40 by 4's, 40 to 100 by 5's, 110 to 180 by 15's, and 200, 220, 240, 250.

The gauges that you're more familiar with began with the "US Standard Gauge" for tax-levying purposes in 1893. They defined the mass of a cubic foot of wrought iron to be 480 lb. A 1 foot by 1 foot by 1/2" sheet would weigh 20 pounds, or 320 ounces, and the gauge for sheet steel weight 320 ounces per square foot was defined at 7/0. From #7/0 to #0, the sequence went down by 20 ounces, 320, 300, ..., 180. Then from #0 to #14 it went down by ten ounces; from #14 to #16 by five ounces; from #16 to #20
by four ounces; from #20 to #26 by two ounces, from #26 to #31, ounc ounce, from #31 to #36, by half an ounce, and from #36 to #38, a quarter of an ounce. In this scheme, assuming that 480 lb is the weight of a cubic foot of sheet metal, #16 is 1/16" an inch - a nice round number.

But no, life couldn'tbe that simple!

The US standard gauge wasn't very useful, because most sheet metal was rolled steel, not wrought iron, and rolled steel weighed closer to 502 pounds per square foot. It was never clear whether steel was being sold/taxed by thickness or by weight per square foot."

After two years of confusion, the American Railway Master Mechanics Association called for a return to the decimal gauge. Since then, the decimal gauge has often been called the "Master Mechanics Gage".

Despite this plea, most of the manufactures continued to use a variant of the US standard gauge, interpreted by weight and not by thickness.
This is called the "Manufacturer's Standard Gauge", and is the one in common use in the US for sheet steel. This is why #16, which was originally 1/16"=0.0625" thick in the US Standard gauge, is actually 480/502 this thickness, or 0.0598".

Aluminum, copper, magnesium, and zinc are measured in completely different gauge(s) and have stories of their own!

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