Sheet Metal Gauge Chart and How to Choose a Thickness

Sheet metal is described two ways that don’t always agree: by gauge number, the trade’s old shorthand, and by thickness in inches or millimeters — the number a micrometer reads and a laser’s cut settings are keyed to. This guide puts them side by side for every metal stocked for fiber laser cutting, explains why the same gauge means a different thickness in steel, stainless, galvanized and aluminum, and shows how thickness changes a part’s strength, weight, hole sizes and price.

Sheet metal gauge chart

This chart is drawn from the live catalog, so it lists exactly the thicknesses stocked for laser cutting today. Steel and stainless sheet carry their gauge, plate carries its fraction, and aluminum, brass and copper read by the decimal. Read across a row to see which metals come in that thickness.

The values are nominal. Real sheet runs a few thousandths either side of the chart, which matters for slot fits and stacked assemblies — measure the sheet when a fit depends on it, and say so in the notes for the shop.

Why gauge numbers run backwards

Gauges started in wire drawing, where a higher number meant the wire had been pulled through more dies and come out thinner. Sheet gauges kept the habit: the higher the gauge, the thinner the metal. The steps aren’t even, either — the jump between neighboring gauges is bigger at the heavy end of the scale than at the light end — so counting gauges is no substitute for reading the decimal. For steel, the Manufacturers’ Standard Gauge ties each number to a weight per square foot, which is why a gauge is a close approximation of thickness rather than a measurement of it.

Same gauge, different thickness

The catch is that each metal family keeps its own gauge table:

• Mild steel follows the Manufacturers’ Standard Gauge — the gauge column in the chart.
• Stainless once had its own table, close to steel’s but not identical, and mills now often sell it by the decimal. The chart shows stainless at the decimal it’s stocked in; order by that number.
• Galvanized sheet has a galvanized gauge that counts the zinc coating, so it runs slightly thicker than bare steel of the same number. The chart lists galvanized at the plain-steel decimal for its gauge; expect the coated sheet to measure a few thousandths more.
• Aluminum uses a different scale altogether — the one wire gauges use — so 16-gauge aluminum is noticeably thinner than 16-gauge steel. Aluminum is bought by its decimal thickness, which is how the chart lists it.
• Brass and copper are ordered by the decimal too. Copper is sometimes called out by weight, in ounces per square foot; convert that to a thickness before ordering.

The safe habit: whenever a drawing or spec sheet says “gauge,” name the metal and write the decimal from the chart beside it. “16 ga” alone is ambiguous; “16 ga mild steel” with its decimal isn’t.

How thickness changes strength and stiffness

Doubling the thickness of a flat plate doesn’t double its stiffness — it multiplies it by about eight, because resistance to bending grows with the cube of the thickness. Bending strength grows with the square, so the same plate also gets about four times stronger. That’s why one step up in gauge can turn a cover that drums and flexes into a solid panel. It also explains why folded parts are so efficient: a flange adds depth, and depth is what stiffness rewards. Parts from the laser ship flat, so any bending happens afterward, with you or a fabricator.

For parts that carry real load — brackets, base plates, gussets — size the thickness from the load, the span and the fasteners, or have whoever engineers the structure call it out. The laser cuts the part to the drawing; it doesn’t rate it.

How thickness changes weight

Weight follows thickness directly: twice as thick, twice as heavy, for the same outline. To estimate a part, multiply its area by its thickness and by the metal’s density. Steel and stainless weigh a little under 0.3 lb per cubic inch, aluminum about 0.1, and brass and copper a little over 0.3. A flat part 12 inches square cut from quarter-inch steel weighs about 10 lb; the same part in aluminum, about 3.5 lb.

Aluminum is the usual way to take weight out. At the same thickness it’s about a third the weight of steel, but also about a third as stiff, so an aluminum part usually goes thicker than the steel part it replaces — and still ends up lighter.

How thickness changes holes, slots and detail

On the laser, the smallest clean features grow with the metal: plan on holes of about half the material thickness or more, slots no narrower than the material thickness, and at least the material thickness of metal between cuts and out to the edge. So the thickness you choose also sets how fine the design can be.

Thin sheet takes fine lettering, tight perforation patterns and small holes; plate needs bolder features. If a design depends on detail — a logo with thin strokes, a dense screen — check it against the thickness before you commit, or choose a thinner sheet and stiffen it another way. The laser file prep guide covers the rest of the design rules. Fine profiles in thick or hardened metal, held tighter than a laser cut, are wire EDM work, quoted on request.

Thickness matters after cutting, too. Threads need enough metal to grip — a common rule of thumb is two or three full threads of engagement, which thin sheet can’t give — so use a nut, a rivet nut, a thicker plate or a machined part; CNC milling is quoted on request. And if you’ll form the part, thicker sheet needs a larger bend radius and more force.

How thickness changes the price

Thickness moves a laser quote in three places:

• Metal: billed by the area each part uses, at a rate that rises with thickness and with the metal — a square foot of plate costs more than a square foot of thin sheet, and stainless, brass and copper cost more than mild steel.
• Cutting: thicker metal cuts slower, so every inch of cut length costs more.
• Pierces: the beam punches through before each hole or cutout, and that takes longer in plate — so a pattern of small holes gets expensive fastest in thick metal.

So the cheapest thickness is the thinnest one that does the job. Price the part at two thicknesses in the laser quote — it re-prices as you switch — and let the numbers say whether the stiffer option is worth it. The pricing page shows example steel brackets and aluminum plates priced the same way.

Starting points by part

• Covers, enclosure panels and electrical boxes: thin-gauge sheet, stiffened by its folds or by fastening along the edges
• Wall-mounted signs and decorative panels: mid-gauge sheet; heavier for freestanding signs and anything that catches the wind
• Brackets, tabs and mounting plates: heavy-gauge sheet to light plate, sized to the load and the fasteners
• Base plates, gussets and structural parts: plate, specified by whoever engineers the structure
• Welded assemblies: thick enough for the welding process — very light sheet is the hardest to weld cleanly
• Outdoor parts in Las Vegas: choose the metal first — stainless, aluminum or galvanized — then the thickness

Each metal’s guide lists its stocked grades and thicknesses, and the quote picker always shows what’s in stock today.