Sheet metal gauge chart

The one that governs the product they sell, which is settled by the material and not by the word gauge. A carbon steel service center quoting 16 ga means 0.0598 in under the Manufacturers' Standard Gauge; the same number from a galvanized coil supplier is 0.0635 in including zinc; from a stainless house it is 0.0625 in under the 1893 gauge; from an aluminum distributor it is 0.0508 in under Brown & Sharpe. If a quote covers more than one material, the gauge number cannot be shared between the lines, and the honest fix is to have the decimal thickness written on the purchase order next to it.

Because it began as a count of operations rather than a measurement. Wire was made by drawing rod through progressively smaller holes in a drawplate, and the number recorded how many passes it had taken — more passes, thinner wire, higher number. Brown & Sharpe formalized that practice in the 1850s as a geometric series, which is the aluminum column here and the AWG series a wire gauge chart uses. When sheet came to be sold by gauge, the weight-based standards inherited the direction of the numbering without inheriting the drawplate, and the count has been backwards ever since.

No, those numbers do not exist in those standards. The galvanized series runs 8 to 30 and the stainless series 7 to 30, while steel and aluminum run 3 to 38, so some numbers are simply outside the range of one standard while being ordinary in another. Filling the gap from the adjacent column would produce a thickness nobody sells, which is worse than an empty cell — 7 ga galvanized would come out at 0.1831 in, and the reason it is not offered is that at that thickness the material is handled as plate and hot-dip coated afterward rather than sold as gauged galvanized coil.

Steel plus zinc, which is the trap in this column. The Galvanized Sheet Gauge takes the same weight per square foot the steel gauge uses and adds 2.5 oz/ft² for the coating on both faces before dividing by 41.82, so 16 ga galvanized is 0.0635 in over the paint-ready surface and the load-bearing steel inside it is one MSG step thinner than a bare 16 ga sheet. For a structural calculation you want the base metal thickness; for a bend allowance, a brake tonnage or a fit-up you want the 0.0635 you can measure. The 2.5 oz/ft² in the definition is a nominal close to a G90 coating, so a G60 or a G115 order shifts the real figure by a thousandth or two.

Almost certainly not — 0.0007 in over nominal is inside the mill tolerance and is what ordinary coil looks like. Gauge is a nominal thickness, and cold-rolled sheet in this range ships to a band that is a few thousandths wide, which is a noticeable percentage of a sheet six hundredths of an inch thick. Two things are worth checking before suspecting the material: measure on the mill edge rather than on a sheared or formed edge, where the metal has been thinned or upset, and look at what the same reading would be called in the other three standards. A reading that is a much better fit for a different standard's number is the real signal that the material is not what the invoice says.

Around 3/16 in for steel, which is between 7 and 6 gauge, and the changeover is commercial rather than defined. Above it the material is ordered as plate by decimal or fractional thickness — 1/4 in, 3/8 in, 1/2 in — because the gauge series becomes coarse there and because plate is produced and tested differently from coil. The chart runs to 3 gauge because the standard does, but almost nothing above about 10 gauge is bought by number in practice. At the other end, 38 gauge is a quarter pound per square foot and the trade calls it foil rather than sheet.

Because the two are stocked to standards written sixty years apart against different reference metals. The 1893 US Standard Gauge converts its weight series at 40 lb per square foot per inch, the figure for wrought iron at 480 lb/ft³, and stainless sheet inherited it. The Manufacturers' Standard Gauge, written later for rolled sheet steel, converts the same weight series at 41.82. Same weights, different divisor, so every stainless number comes out about 4.5% thicker than the steel number beside it. The tell is the arithmetic: the stainless column lands on clean fractions — 18 ga is exactly 0.0500 in, 11 ga exactly 1/8 in — and the steel column never does.