Sheet Metal Gauge Chart: Thickness by Material and Standard

A sheet metal gauge chart converts a gauge number into the actual thickness of a sheet in a specific material. Gauge runs on an inverse scale, so a lower number means a thicker sheet. The same number also maps to a different thickness in steel, stainless steel, aluminum, and galvanized sheet.

At 16 gauge, stainless steel is nearly a quarter thicker than aluminum. A gauge number quoted without its material leaves the real thickness open to interpretation, and that gap is large enough to change bend allowances, hardware fit, and part stiffness.

The charts below give nominal thickness in inches and millimeters for each material, with the standard that governs it and the thickness tolerance a mill is permitted to ship.

Why Do Gauge Numbers Differ Between Materials?

The gauge system predates decimal thickness callouts, and each metal ended up with its own table rather than a shared one. A metal sheet gauge chart, therefore, holds only for the material it was built for. Related conversion and design references sit alongside this chart in the sheet metal guides library.

What does a gauge number actually measure?

Gauge derives from sheet weight per square foot rather than from a linear thickness unit. The Manufacturers Standard Gage for steel is based on 41.82 pounds per square foot per inch of thickness, so every steel gauge value traces back to that single constant.

The stainless series follows the older U.S. Standard Gauge for sheet iron and steel, and aluminum follows the wire-derived Brown and Sharpe progression.

The step between adjacent gauge numbers shrinks toward the thin end of each series. In the stainless series, 3 gauge to 4 gauge is a step of 0.0156 inches. From 24 gauge to 25 gauge, the step is 0.0031 inches, roughly one-fifth as large.

Which standard governs each material?

Gauge series are industry conventions, and ASTM product standards set the dimensional tolerances that apply to the finished sheet. Naming both alongside the gauge number makes a thickness callout checkable at receiving inspection. A supplier quoting gauge alone has quoted a number, not a dimension.

The table below pairs each material with its gauge series and the product standard that governs its tolerances.

Table 1. Gauge series and governing product standard by material

The steel and stainless series sit close enough at some gauge numbers to look interchangeable, though they differ at every one. Aluminum sits furthest from both, because the Brown and Sharpe series comes from non-ferrous wire practice rather than from rolled steel.

A sheet metal gauge conversion chart between materials works only through thickness, which is why each material gets its own table below.

What happens when the material is left out?

A 16-gauge callout answered in aluminum instead of stainless delivers 19% less thickness. Bending stiffness scales with the cube of thickness, so the part gives up roughly 46% of its section stiffness before the lower elastic modulus of aluminum is counted.

Standard Steel Sheet Metal Gauge Chart

Mild steel and carbon steel sheets run on the Manufacturers Standard Gage, with thickness tolerances set under ASTM A568. The steel sheet metal gauge thickness chart below converts each gauge number in common fabrication use into inches and millimeters.

All values are nominal, and the tolerance section gives the band a mill is permitted to ship against.

Table 2. Mild and carbon steel, Manufacturers Standard Gage, tolerances per ASTM A568

Carbon steel thicker than 7 gauge is usually ordered by fractional or decimal thickness rather than by gauge number. At 0.1196 inches, 11 gauge is often mistaken for 1/8 inch, which is 0.125 inches.

The millimeter column is a conversion rather than a separate standard. The inch values define the series, and the millimeter figures convert them at 25.4 mm per inch. Mills working to metric sheet standards roll to preferred metric thicknesses instead, so a 1.5 mm sheet and a 16-gauge sheet at 1.519 mm are separate specifications.

Most enclosure, bracket, and chassis work in carbon steel sits between 20 gauge and 10 gauge, or 0.0359 to 0.1345 inches.

Thinner material saves weight at the cost of stiffness. Thicker material raises press brake tonnage and increases the minimum bend radius.

Cold-rolled sheet holds a tighter thickness band and a smoother surface than hot-rolled sheet, so it is the usual choice for thinner gauges and cosmetic panels. Hot-rolled, pickled, and oiled sheet is common toward the thick end of the chart, since cost there carries more weight than surface finish.

Stainless Steel Sheet Metal Gauge Chart

Stainless steel sheets run on their own gauge series, separate from the carbon steel table above, with dimensional tolerances set under ASTM A480.

The stainless steel metal gauge chart below gives nominal thickness for each gauge number in inches and millimeters. The grade does not change the table, so the 304 and 316L sheets at the same gauge share the same nominal thickness.

Table 3. Stainless steel sheet, stainless gauge series, tolerances per ASTM A480

Stainless reads thicker than mild steel at every shared gauge number. At 16 gauge, stainless is 0.0625 inches against 0.0598 inches for mild steel, a difference of 0.0027 inches. At 10 gauge, the gap grows to 0.0061 inches.

That difference looks like rounding on a drawing, but it changes the bend deduction at the press brake. The same tooling and the same program return a different flange length in each material.

Springback adds to the difference. Austenitic grades such as 304 and 316L work-harden during forming and recover more angle after the punch lifts than carbon steel of the same thickness. Overbend allowances set for mild steel are reset against the stainless thickness before the first production bend.

Aluminum Sheet Metal Gauge Chart

Aluminum sheet uses the Brown and Sharpe series, also known as the American Wire Gauge, with dimensional tolerances set under ASTM B209. The series follows a different mathematical progression from the steel gauges rather than an adjusted version of them.

The aluminum sheet metal gauge chart below gives nominal thickness at each gauge size in inches and millimeters.

Table 4. Aluminum sheet, Brown and Sharpe series, tolerances per ASTM B209

Aluminum diverges furthest from the steel tables. At 10 gauge, aluminum is 0.1019 inches against 0.1406 inches for stainless, a gap of 0.0387 inches, or close to 1 mm. In metric terms, that is 2.588 mm for aluminum against 3.571 mm for stainless.

The gap narrows in absolute terms toward the thin end, falling to 0.0117 inches at 16 gauge and 0.0049 inches at 24 gauge. In proportion, aluminum still runs roughly 19 to 28% thinner than stainless between 10 gauge and 24 gauge.

Alloy selection sits on top of the gauge decision. Aluminum 5052 is a common choice for formed enclosure work because it bends at tight radii without cracking. Aluminum 6061-T6 is stronger and less forgiving in forming, so it is usually specified for machined or lightly formed parts.

Some distributors list aluminum against the steel gauge table rather than the Brown and Sharpe series. Confirming which series a quote uses, or quoting in decimal inches or millimeters, settles the question at the order stage.

Galvanized Sheet Metal Gauge Chart

Galvanized sheet runs on the carbon steel series, with coating classes and the coated product defined under ASTM A653.

The galvanized sheet metal gauge chart below shows two figures at each gauge: the base steel thickness and the published galvanized gauge thickness.

Table 5. Galvanized steel sheet, base steel per the Manufacturers Standard Gage and published galvanized gauge values, coating classes per ASTM A653

The two columns exist because suppliers quote from either one. The published galvanized gauge runs about 0.0037 inches above base steel at every gauge number. That figure is an allowance built into the series, not the measured thickness of any particular coating.

The coating itself is thinner than that allowance. A G90 coating carries 0.90 ounces of zinc per square foot across both faces, which adds roughly 0.0016 inches to total thickness. G60 adds roughly 0.0011 inches, and heavier classes add proportionally more.

At 16 gauge, base steel is 0.0598 inches, a G90 sheet measures close to 0.0614 inches, and the published galvanized gauge lists 0.0635 inches. A drawing that names galvanized sheet without the base thickness and coating class leaves that difference open.

Clearances come off the coated thickness. Hole diameters, slot widths, clinch hardware grip ranges, and assembly gaps all see the zinc, so they are sized from the coated figure rather than the base metal.

The coating also changes forming and joining. Zinc can mark the surface against press brake tooling on tight radii, so tool polish and protective film carry more weight than on bare steel.

Welding galvanized sheet usually calls for the coating to be removed back from the joint, with ventilation, because zinc vaporizes well below the melting point of steel. Setup for galvanized sheet metal forming accounts for both before the first bend.

Sheet Metal Thickness Tolerance

Every figure in the four charts above is nominal. Sheet arrives inside a permitted band around that nominal, and the product standard sets the band rather than the fabricator.

Sheet metal thickness tolerance is the width of that band, and it is often wider than drawings assume.

How much thickness variation is permitted at each gauge?

Mills ship against a tolerance band defined by thickness range and sheet width. The table below gives representative cold-rolled carbon steel bands under ASTM A568, and the current edition of the standard governs any purchase order.

Table 6. Cold-rolled carbon steel sheet thickness tolerance, representative bands per ASTM A568

The table reads two ways. In proportion, the band is widest at the thin end, since +/-0.002 inches on a 0.0120-inch sheet is a variation of about 17%. In absolute terms, it is widest at the thick end, and the full 0.018-inch band at 9 gauge exceeds the 0.0149-inch step to 8 gauge.

Stainless steel under ASTM A480 and aluminum under ASTM B209 carry their own tolerance tables. The figures differ in detail, and the same pattern applies, with thicker and wider sheet opening the band.

A sheet at either limit is compliant material and is certified as such.

Why does sheet width change the tolerance?

Rolling mills hold thickness less consistently across a wider strip. The rolls deflect under load toward the center of the barrel, and that deflection grows with rolled width, so the permitted band opens as width increases.

Specifying a narrower coil or sheet width can tighten the incoming thickness band at no tooling cost. The option suits parts whose thickness feeds a fit calculation. When a build depends on the measured figure rather than the nominal, measured thickness can be requested with the mill test report at the order stage.

What does thickness variation change downstream?

The operations that follow are set from thickness rather than from gauge number. Each one is calibrated against a nominal figure and shifts when incoming material sits near an edge of its band.

The table below sets out five places the variation shows up.

Table 7. How incoming thickness variation shows up in production

Press brake work carries the largest cumulative effect, because the shift repeats at every bend. On a six-bend part, a flange that measures correctly after the first bend can sit off the drawing dimension by the last.

Two separate tolerances apply to every sheet metal part. Mill tolerance governs the thickness of the sheet that arrives from the mill. Process tolerance governs what the fabricator holds on the finished part, and it depends on the cutting and forming method, as set out in the guide to tolerancias de piezas de chapa metálica.

How should thickness be specified on a drawing?

Gauge ambiguity has a direct fix in the callout format. A complete thickness callout carries three items in order: the decimal thickness, the gauge number, and the governing standard. Written out, that reads as 0.0598 inches, 16 gauge, per ASTM A568.

A supplier reading that callout has the dimension, the series it came from, and the tolerance band that applies. Galvanized parts add a fourth item, stating whether the figure is base metal or coated thickness and naming the coating class.

Metric sourcing follows the same logic. A callout of 1.5 mm with a stated tolerance, rather than 16 gauge, gives a mill working to metric sheet standards a thickness it can roll directly.

For parts whose thickness feeds a fit calculation, the drawing can carry its own tolerance rather than the mill default. A sheet specified at 0.0598 inches +/-0.002 inches typically costs more than standard commercial sheet, and it settles the question before assembly.

A gauge chart gives the starting figure, and the decimal thickness, standard, and tolerance written on the drawing decide what actually arrives. Solución Yijin works from the base or coated thickness relevant to each job and verifies incoming sheet thickness against the drawing specification before forming begins.  Engineers specifying sheet thickness can Envíe un plano for a gauge and thickness tolerance review.

Sheet Metal Gauge Chart FAQs

Is 16 gauge thicker than 18 gauge sheet metal?

A 16-gauge sheet is thicker than an 18-gauge sheet in every material covered here, by roughly 20%. In carbon steel, the comparison is 0.0598 inches against 0.0478 inches. In stainless steel, it is 0.0625 inches against 0.0500 inches, and in aluminum, it is 0.0508 inches against 0.0403 inches.

How is delivered sheet thickness verified?

Delivered sheet thickness is verified with a calibrated micrometer at several points across the sheet and at a set distance in from the edge. For stainless steel, ASTM A480 places that point at least 3/8 inch, about 9.5 mm, in from the edge, since rolled edges do not represent the body of the sheet. Readings at the center and both quarter points show variation across the width.

Does the gauge system apply to plate?

The gauge system does not apply to plate, which is called out by fractional or decimal thickness. In US practice, carbon steel is usually treated as plate from 3/16 inch, about 4.8 mm, while many metric suppliers draw the line at 6 mm. Aluminum is classed as plate from 0.250 inches.

Can a gauge number be converted between materials?

A gauge number cannot be converted directly between materials because the conversion runs through thickness. The gauge number becomes a decimal thickness in the first material, and that thickness is matched to the nearest gauge in the second material using its own table. The nearest match is rarely exact, so the decimal thickness is the figure that travels on the drawing.

What does a mill test report confirm about thickness?

A mill test report confirms that the heat supplied meets the ordered specification. It lists the ordered dimensions alongside chemical composition, mechanical test results, and the heat number that ties the certificate to the material. Measured thickness appears on some reports only, so buyers who need the actual figure can request it at the order stage.

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