Sheet Metal Materials & Gauge Charts

Sheet metal is a flat stock of metal thin enough to be sheared, bent, punched, or stamped into shape, and the choice of material and thickness drives almost every downstream decision in a fabrication job. The material sets strength, corrosion resistance, weight, and cost, while the thickness, expressed either as a gauge number or directly in millimeters, sets how the sheet behaves under the press brake, the laser, and the punch. A bracket that must hold a load, an enclosure that must resist rust, and a panel that must bend cleanly each call for a different combination of alloy, temper, and gauge, and a mismatch at this stage shows up later as a cracked bend, a warped panel, or a part that corrodes in service.

This guide covers the four families of sheet metal that account for most fabrication work: aluminum, stainless steel, carbon steel, and the copper alloys. It explains how to read the gauge system and why a 16 gauge sheet of steel is not the same thickness as a 16 gauge sheet of aluminum, then walks through how to choose a material by application, how formability and bending differ between alloys, and the tolerances and design rules that keep a part manufacturable.

Sheet metal materials overview

The four material families cover a wide spread of strength, corrosion resistance, formability, and cost, and within each family the specific alloy and temper do much of the work. Picking the family first, then the grade, is the practical way to narrow the choice.

Aluminum

Aluminum is the light sheet metal, at a density of about 2.68 to 2.70 grams per cubic centimeter, roughly a third that of steel. It is non-magnetic, conducts heat and electricity well, and forms a tough oxide skin that gives it good natural corrosion resistance. In sheet form it is the default where weight matters more than raw strength, such as panels, enclosures, and brackets that must be carried, and in marine service where the right grade shrugs off saltwater.

The three common sheet alloys split cleanly by purpose. Aluminum 5052, usually supplied in the H32 temper, has a tensile strength of 31 to 43 ksi and is the best-forming of the three, with the lowest springback under the brake. It is the marine-grade alloy, with excellent corrosion resistance in saltwater, and is the first choice for any part that will be bent, drawn, or formed. Aluminum 6061, most often T6 temper, reaches a tensile strength of 45 ksi and machines very well, but it is not recommended for complex bending in the T6 temper because the heat-affected zone softens and the alloy springs back 5 to 10 degrees; for a part that must be both machined and bent, the T4 or T651 temper is the better choice. Aluminum 7075-T6 is the strongest of the three at 83 ksi tensile, but it is primarily an aerospace plate and bar alloy, and in sheet form it should not be bent because it cracks at the bend line.

Stainless steel

Stainless steel is the corrosion-resistant sheet metal, an iron alloy with enough chromium, at least 10.5 percent, to form a passive oxide film that protects the surface. It is dense, at about 8.00 grams per cubic centimeter, strong, and hard, and it holds a finish that makes it the standard for food, medical, and architectural work. The two common sheet grades are 304 and 316.

Stainless 304, often supplied as 304 or the low-carbon 304L, has a tensile strength of 73 to 87 ksi and is the workhorse stainless for general fabrication. It forms and draws well, welds readily, and resists most atmospheric and chemical corrosion. Stainless 316 adds 2 to 3 percent molybdenum, which is the key differentiator, and that molybdenum resists chloride pitting, so 316 is the grade for marine hardware, coastal architecture, and chemical service. The molybdenum comes at a price: 316 costs about 15 to 30 percent more than 304, and it pays off only in chloride-rich or chemical environments, so for inland general fabrication 304 is usually the more economical and equally serviceable choice. Both grades machine at about 45 percent the rate of free-machining brass, so they call for sharp tooling and lower speeds.

Carbon steel

Carbon steel is the strong, economical, and weldable sheet metal, the default for structural and general fabrication where corrosion resistance is handled by coating rather than by alloying. It is dense, at about 7.85 grams per cubic centimeter, and its strength rises with carbon content. The common sheet grades are A36, with a tensile strength of 58 to 80 ksi, the structural standard for plates, brackets, and frames; 1018, a low-carbon grade at 65 to 85 ksi that machines and welds well; and 1045, a medium-carbon grade at 80 to 100 ksi that takes heat treatment for higher-strength parts.

For corrosion protection, carbon steel sheet is often galvanized, which means coated with a layer of zinc, usually by hot-dip, to a designation such as G60 or G90 that sets the coating weight. The zinc sacrifices itself to protect the underlying steel, so a galvanized sheet resists rust in outdoor, HVAC, and enclosure service where bare carbon steel would corrode. The coating changes how the sheet behaves under heat: in welding the zinc burns off and risks porosity, so the coating is ground back from the weld zone, and in laser cutting the zinc vaporizes at about 900 degrees Celsius, which is why a nitrogen assist gas is recommended for a clean, oxide-free edge. At tight bends a thick G90 coating can flake, so the bend radius and coating weight must be set together.

Copper and brass

Copper and brass are the conductivity and decorative sheet metals, used in smaller volumes than steel or aluminum but where their specific properties are essential. Copper C110, electrolytic tough pitch, has an electrical conductivity of 101 percent IACS, the benchmark against which all conductors are measured, and it is the material for busbars, ground straps, and electrical conductors. It is soft, ductile, and forms readily, but it is highly reflective at the fiber laser wavelength, so cutting it calls for a specialized setup or a waterjet. Brass, in the C260 cartridge grade, is ductile and forms well for deep drawing and spinning, while the free-machining brass C360 sets the 100 percent machinability benchmark against which all other metals are rated. Brass carries a decorative warm tone and good corrosion resistance, which suits it to hardware, connectors, and trim.

The sheet metal gauge system

The gauge is a traditional thickness scale inherited from the wire-drawing trade, and its single most important feature is that the gauge number runs inverse to thickness: a lower gauge number means thicker metal, and a higher gauge number means thinner metal. The scale comes from the practice of drawing metal through progressively smaller dies, where each pass thinned the stock one step, so a higher draw number, which became the gauge number, meant a thinner result. The convention stuck, and gauge numbers remain the common shorthand in North American shops even though the actual thickness is what the machines cut and bend.

Steel gauge vs aluminum gauge vs stainless

The critical fact about the gauge system is that steel, galvanized steel, aluminum, and stainless each use a different gauge scale, so the same gauge number is a different thickness in each material. A 16 gauge mild steel sheet is about 1.52mm thick, a 16 gauge aluminum sheet is about 1.29mm, and a 16 gauge stainless sheet is about 1.51mm. The scales diverge because each was standardized against a different reference weight and material, and that divergence is why a gauge number alone is never enough to specify a part. The practical rule is to state the actual thickness in mm or inches as the controlling dimension and treat the gauge as a stock reference. This is doubly important when a drawing moves between steel and aluminum, because a gauge-only callout produces a part of the wrong thickness.

Why gauge matters for bending and cost

Gauge, which is to say thickness, sets how the sheet bends and what it costs. The minimum inside bend radius scales with thickness, and the press tonnage required to form the bend scales with thickness and material strength, so a thicker or harder sheet needs a larger radius and a heavier press. Thickness also sets the cost: sheet metal is quoted by weight and by area, so a thicker gauge costs more per square meter and takes longer to cut. The economic choice is the thinnest gauge that meets the load, corrosion, and formability requirements, not the thickest that fits the budget.

Choosing a material by application

Material selection comes down to four properties traded against cost: strength, corrosion resistance, formability, and weight. Each family has a clear lane.

Choosing by strength

When raw strength leads, carbon steel is the economical choice, with A36 at 58 to 80 ksi and 1045 at 80 to 100 ksi covering most structural needs. Stainless 304 and 316 reach 73 to 87 ksi while adding corrosion resistance, at a higher price. For high strength at low weight, aluminum 7075-T6 hits 83 ksi at a third of steel’s density, though it is not a bending alloy, and aluminum 6061-T6 at 45 ksi is the practical structural aluminum for machined parts.

Choosing by corrosion resistance

The corrosion ladder runs from bare carbon steel, which rusts and must be coated, through galvanized steel, which protects itself with zinc, to the stainless grades, which resist by alloying. Aluminum 5052 is the marine-grade aluminum and resists saltwater well, while 6061 needs anodizing for marine service. Among stainless grades, 304 handles most atmospheric and food-service corrosion, and 316 adds the molybdenum that resists chloride pitting in marine and chemical environments, at a 15 to 30 percent premium that pays off only there.

Choosing by formability

When the part will be bent or drawn, formability leads. Aluminum 5052-H32 is the best-forming of the common alloys, with the lowest springback, and it is the default for complex bends. Mild steel bends well with moderate springback and is the economical forming choice. Stainless 304 and 316 draw well but spring back about 5 to 12 degrees and need higher force. Aluminum 6061-T6 is the cautionary case: usable for simple bends with a generous radius, but not suited to complex forming, and 7075-T6 should not be bent at all.

Choosing by cost and weight

Cost and weight trade off directly. Carbon steel is cheapest and is the default where weight is unconstrained. Galvanized steel adds the zinc cost for outdoor service. Aluminum costs more per kilogram but weighs about a third as much, so it wins where the part must be lifted or shipped repeatedly. Stainless is the premium sheet metal, and copper and brass are the most expensive families, chosen for conductivity or appearance, not for general structure.

A choose-material decision guide

A simple decision sequence narrows the choice fast. First, ask whether the part must resist corrosion. If yes and the environment is marine, coastal, or chemical, choose stainless 316 or aluminum 5052; if general outdoor or humid, choose galvanized steel, stainless 304, or aluminum 5052. If corrosion is not a concern, move to strength and weight: choose aluminum 6061-T6 for machined parts or 5052-H32 for formed parts where the part must be light, or carbon steel, A36 for structure or 1018 for machined parts, where cost leads. Finally, check formability against the geometry: if the part has complex bends, prefer 5052-H32 or mild steel, and avoid 7075-T6 and 6061-T6 for tight radii.

Formability and bending notes

Minimum bend radius and springback

Formability is the measure of how much a sheet can be bent, drawn, or stretched before it cracks, and it depends on the alloy, the temper, the thickness, and the bend radius. The two practical numbers are the minimum inside bend radius, usually stated as a multiple of the thickness, and the springback, the angle the sheet returns after the press releases.

Aluminum 5052-H32 is the standout former, with a minimum bend radius of about 1 to 1.5 times the thickness along the grain and springback of only 1 to 3 degrees. It can be bent to 90 degrees around a pin of radius 1.5 times the thickness without cracking, which is why it is the first choice for formed panels and enclosures. Mild steel bends well too, with springback of about 3 to 10 degrees, and it tolerates a minimum inside radius of about 0.5 times the thickness for soft tempers. Stainless 304 and 316 form and draw well but spring back more, about 5 to 12 degrees, and need higher press force because of their higher yield strength; the inside bend radius should be at least 0.5 times the thickness, and tighter for thicker gauges.

Aluminum 6061-T6 is the alloy that catches out the unwary. In the T6 temper it is strong but not ductile, and complex bends can crack at the heat-affected zone. The minimum bend radius for 6061-T6 runs from about 2 to 6 times the thickness along the grain, depending on gauge, and the springback of 5 to 10 degrees must be overbent to hit the target angle. For a part that must be both bent and machined, the T4 temper, which is naturally aged and more ductile, or the T651 temper, which is stress-relieved by stretching, are the safer choices. Aluminum 7075-T6 should never be bent in the T6 temper; it cracks at the bend line, and if a 7075 part must be formed, it should be bent in the annealed O temper and heat-treated afterward.

Checklist

• State the exact material, alloy, and temper, such as aluminum 5052-H32 or stainless 316L, not just aluminum or stainless.
• State the actual thickness in mm or inches as the controlling dimension, and add the gauge as a stock reference, not a substitute.
• Set the inside bend radius to at least 0.5 times the thickness for soft materials, and 2 to 6 times the thickness for harder tempers such as 6061-T6 bent along the grain.
• Account for springback by material when planning bends: 1 to 3 degrees for 5052-H32, 3 to 10 degrees for mild steel, 5 to 12 degrees for stainless, and 5 to 10 degrees for 6061-T6.
• Match the alloy and temper to the operation: 5052-H32 for forming, 6061-T6 or T651 for machined-and-bent parts, 304 or 316 for corrosion service, mild steel for economical structure.
• For galvanized steel, plan for the zinc coating: grind it back at weld zones, and specify a nitrogen assist gas if the sheet will be laser cut.

Design rules

• Always state the actual thickness in mm or inches, not just the gauge, to avoid the 25.4x scale risk and the steel-vs-aluminum gauge mismatch.
• Specify the alloy and temper explicitly, because the same material name spans very different behavior; aluminum 6061-T4 bends where 6061-T6 cracks.
• Keep the inside bend radius at or above the material minimum, and bend across the grain where a tighter radius is needed, because bending along the grain raises the cracking risk.
• Set the minimum flange height to at least 3 times the thickness, and space bends at least 4 times the thickness apart, so the die can reach the bend without interference.
• For stainless and harder tempers, allow for higher springback and higher press force in the tooling plan, and overbend to compensate.
• State the units in the drawing, the filename, and the order, because a millimeter-vs-inch mismatch produces a part 25.4 times the intended scale, the most common and most expensive file-format error in custom sheet metal.

Tolerances

Cut, bend, and linear tolerances

Sheet metal tolerances span the cut, the bend, and the formed dimension, and each has a typical commercial band. Laser cutting of mild steel holds about plus or minus 0.10mm on thin gauges up to 3mm, widening to about plus or minus 0.50mm on thicker stock from 12 to 25mm. Bend angle tolerance runs about plus or minus 1.0 to 2.0 degrees for carbon steel at standard commercial quality, tightening to about plus or minus 0.5 degrees with good tooling, and stainless holds about plus or minus 1.0 to 1.5 degrees. Linear dimensions on a bent part typically hold about plus or minus 0.25mm for carbon steel.

The minimum bend radius is the tolerance most often missed. It scales with thickness and material: at least 0.5 times the thickness for soft materials such as 5052-H32 and annealed mild steel, rising to 1 to 2 times the thickness for 304 in thicker gauges, and 2 to 6 times the thickness for 6061-T6 along the grain. A radius below the material minimum risks a crack at the bend line, so the radius is set from the material and temper, not from the geometry alone, and tighter radii are reached by bending across the grain or by switching to a more formable alloy.