Sheet metal is metal rolled into thin, flat pieces, usually less than about 1/4 inch thick, that can be cut, bent and formed into parts. In construction it almost always means steel sheet, plain, galvanized or aluminum-zinc coated, though aluminum, stainless steel and copper sheet are common too.
This guide explains how sheet metal is made, how thickness is measured, the main types and the ASTM specifications behind them, and where each one is used, from ductwork and roofing to metal studs and floor deck.
Sheet vs Plate vs Foil
Flat-rolled metal is grouped by thickness. Foil is the thinnest and is mostly used for packaging and insulation facings. Sheet is the middle range and is the material for panels, flashing, ducts and light framing. Plate is the heavy end, used for base plates, gusset plates and fabricated beams.
There is no single universal cutoff between sheet and plate. Product standards and supplier catalogs set their own limits, and the line usually falls somewhere around 3/16 to 1/4 inch. If you are ordering, describe the thickness in inches or millimeters as well as the gauge so there is no confusion.
How Sheet Metal Is Made
Steel sheet starts as a thick cast slab. The slab is reheated and squeezed through a series of rolling stands until it is thin enough to be coiled. That product is hot-rolled sheet, and it carries a dark oxide scale. Some of it is sold as is. The rest is pickled to remove scale and then rolled again at room temperature, which makes cold-rolled sheet: thinner, flatter, with tighter thickness tolerances and a smooth surface. Our guide to hot rolled vs cold rolled steel covers the differences in more detail.
Cold-rolled coil can then be run through a coating line, where it is dipped in molten zinc or aluminum-zinc, and sometimes through a paint line that bakes on primer and a colored topcoat. The finished coil is slit to width, cut to length or fed into roll formers that shape it into roofing panels, studs, deck and trim.
How Sheet Metal Thickness Is Measured
In the US, steel sheet is usually described by gauge, where a bigger number means thinner metal. The Manufacturers’ Standard Gauge for uncoated steel sheet is based on weight per square foot, which is why the steps between gauges are uneven. A few common sizes:
| Gauge | Thickness (in) | Thickness (mm) | Weight (lb/ft²) | Typical uses |
|---|---|---|---|---|
| 26 | 0.0179 | 0.45 | 0.750 | Light roofing and siding panels, flashing |
| 24 | 0.0239 | 0.61 | 1.000 | Standing seam roofing, ductwork |
| 22 | 0.0299 | 0.76 | 1.250 | Heavier roof panels, floor deck, enclosures |
| 20 | 0.0359 | 0.91 | 1.500 | Framing, deck, brackets |
| 18 | 0.0478 | 1.21 | 2.000 | Structural studs, deck, equipment housings |
| 16 | 0.0598 | 1.52 | 2.500 | Heavy studs, trailer and truck parts |
| 14 | 0.0747 | 1.90 | 3.125 | Heavy-duty brackets, tool boxes, guards |
Values are the Manufacturers’ Standard Gauge for uncoated steel. Galvanized, aluminum and stainless sheet use different gauge tables, so the same number gives a different thickness. Our steel gauge thickness chart lists the full range. Some products are also specified directly in mils or inches; cold-formed steel framing, for example, is commonly ordered by its minimum base-metal thickness in mils.
Types of Sheet Metal and Their Specifications
Most steel sheet sold in the US is made to an ASTM specification. Knowing the spec tells you what you are buying.
| Type | ASTM spec | What it is | Common uses |
|---|---|---|---|
| Hot-rolled sheet | A1011/A1011M | Carbon, structural and high-strength low-alloy sheet and strip, hot rolled | Brackets, trailers, heavier formed parts |
| Cold-rolled sheet | A1008/A1008M | Carbon, structural and high-strength low-alloy sheet, cold rolled | Appliances, cabinets, parts to be painted |
| Galvanized sheet | A653/A653M | Steel sheet hot-dip coated with zinc (or zinc-iron for galvannealed) | Ductwork, studs, deck, roofing, culverts |
| Galvalume (55% Al-Zn) | A792/A792M | Steel sheet hot-dip coated with a 55% aluminum-zinc alloy | Metal roofing and siding |
| Stainless sheet | Various (by grade) | Chromium-bearing alloy, often grade 304 or 316 | Kitchens, food plants, coastal trim |
| Aluminum sheet | Various (by alloy) | Light, non-magnetic, corrosion resistant | Gutters, trim, marine and vehicle panels |
The descriptions above come from the published scopes of ASTM A1011/A1011M-23, ASTM A1008/A1008M-21a, ASTM A653/A653M-23 and ASTM A792/A792M-21 (all checked November 2026). Each spec has designations inside it. A1008, for instance, covers commercial steel (CS), drawing steel (DS), structural steel (SS) in grades from 25 to 80 ksi, and high-strength low-alloy (HSLAS) grades, so “A1008 SS Grade 33” tells a supplier much more than “cold-rolled sheet.”
Coated vs uncoated
Uncoated sheet rusts quickly outdoors, so anything exposed to weather is usually coated. Zinc (galvanized) protects steel even at small scratches because the zinc corrodes first; see what galvanized steel is for how that works. The aluminum-zinc coating on Galvalume is the most common base for painted metal roofing. Both come in several coating weights, and a heavier coating lasts longer in the same environment.
What Sheet Metal Is Used For
- Roofing and siding. Corrugated, ribbed and standing seam panels, mostly galvanized or Galvalume with a baked paint finish.
- HVAC ductwork. Galvanized sheet formed into rectangular and round duct.
- Framing. Cold-formed studs, tracks, joists and purlins are roll-formed from galvanized sheet.
- Floor and roof deck. Fluted deck panels that span between joists or beams.
- Flashing and trim. Drip edges, valleys, gutters and wall caps.
- Manufacturing. Vehicle bodies, appliances, enclosures, machine guards and furniture.
Steel vs Other Sheet Metals
Steel sheet is the cheapest and strongest per dollar, and it is magnetic and easy to weld. Aluminum sheet weighs about a third as much for the same thickness and does not rust, but it is softer and costs more; our steel vs aluminum comparison covers the trade-offs. Stainless sheet resists corrosion without a coating but costs considerably more and is harder to cut and form. Copper and zinc sheet are mostly used for architectural roofing and flashing where appearance matters.
When sheet metal is part of a structure, such as roof deck acting as a diaphragm, load-bearing studs or purlins, its gauge, grade and fastening have to be designed and checked by a licensed structural engineer, not picked from a chart.
FAQ
What is sheet metal made of?
Most sheet metal is low-carbon steel, often coated with zinc or aluminum-zinc. Sheet is also made from aluminum, stainless steel, copper, brass and titanium.
How thick is sheet metal?
Building sheet commonly runs from about 0.018 in (26 gauge) to about 0.075 in (14 gauge). Anything much over 3/16 to 1/4 inch is usually called plate.
Is sheet metal the same as tin?
No. “Tin” is an old name for thin steel sheet, from tinplate, which is steel with a thin tin coating. Modern “tin roofs” are almost always galvanized or Galvalume steel.
Is sheet metal steel or aluminum?
It can be either. In construction and HVAC the default is galvanized steel. A magnet test tells you quickly: steel sheet is magnetic, aluminum is not.
Why does a higher gauge mean thinner metal?
Gauge is a traditional system rather than a measurement. The usual explanation is that it traces back to wire drawing, where each extra pass through a die made the wire thinner and added to the count. Whatever the origin, the steel sheet gauge today is tied to weight per square foot, so always confirm the actual thickness.
Reference information only, not engineering advice. Disclaimer.