Sheet Metal Gauge Calculator

Gauge (often written ga or GA) is a legacy numbering system for sheet-metal thickness. It is inverse — a higher gauge number means a thinner sheet: 10 gauge steel (3.42 mm) is much thicker than 20 gauge steel (0.91 mm). The number originally referred to how many times a sheet had been passed through the rolling mill, which is why it runs backwards and why the steps are uneven rather than a neat decimal ladder.

The catch that trips up almost everyone: gauge is not a single universal scale. Each material grew up with its own standard, so the same gauge number is a different thickness in a different material:

• Uncoated (mild/carbon) steel uses the Manufacturers' Standard Gauge for Sheet Steel, defined on a nominal weight basis of 41.82 lb/ft² per inch.
• Galvanized steel uses the Galvanized Sheet Gauge, which is thicker than the bare-steel gauge because the number includes the zinc coating.
• Stainless steel uses a fraction-of-inch based Stainless Steel Gauge.
• Aluminum, brass and copper use the American Wire Gauge (AWG), also called Brown & Sharpe, defined by a geometric formula.

That is exactly why this calculator keeps four separate, real tables instead of one — and shows all four at once so you can see the difference.

Search "16 gauge in mm" and you will get several different answers — all of them correct, for different materials. Here is 16 gauge on each standard:

Material	16 ga thickness (in)	16 ga thickness (mm)	Weight
Mild / carbon steel	0.0598	1.519 mm	11.92 kg/m² (2.44 lb/ft²)
Galvanized steel	0.0635	1.613 mm	12.66 kg/m² (2.59 lb/ft²)
Stainless steel 304	0.0625	1.588 mm	12.70 kg/m² (2.60 lb/ft²)
Aluminum (AWG)	0.0508	1.290 mm	3.48 kg/m² (0.71 lb/ft²)

A "16 gauge" bracket is 1.519 mm if it is bare steel, 1.613 mm if it is galvanized, and only 1.290 mm if it is aluminum — a 25 % spread from top to bottom. On a fabrication drawing this ambiguity is real money and real rework, which is why good practice is to call out the decimal thickness in mm or inches and treat the gauge number as a convenience label, not a spec. The side-by-side panel in the calculator makes this concrete: pick a gauge and watch four different bars appear.

Once you know the thickness, weight per unit area is elementary — it does not depend on the sheet's length or width, only on its thickness and the material density:

w = ρ · t

with ρ the density (kg/m³) and t the thickness (m). Working in the units a detailer actually uses:

Weight (kg/m²) = ρ (kg/m³) × t (mm) ÷ 1000

For carbon steel (ρ = 7850 kg/m³) that collapses to the handy rule 7.85 kg/m² per millimetre of thickness. So 16 ga steel at 1.519 mm weighs 7.85 × 1.519 = 11.92 kg/m². To convert to imperial, 1 kg/m² = 0.204816 lb/ft², giving 2.44 lb/ft².

The densities this calculator uses:

Material	ρ (kg/m³)	kg/m² per mm
Carbon / mild steel	7850	7.85
Galvanized steel	7850 *	7.85
Stainless steel 304/316	8000	8.00
Aluminum 6061 / 3003	2700	2.70

* The galvanized gauge thickness already includes the zinc, so the weight comes out slightly higher than bare steel of the same gauge; the pure zinc mass of a typical G90 coating adds roughly another 1–3 % on thin sheet. Note the big one: aluminum weighs about one third of steel at the same thickness, which is the whole reason it is used for skins, panels and ductwork where weight matters.

In the shop you usually have the opposite problem — you miked a mystery sheet at, say, 1.60 mm and need to know what gauge to order. Because gauge steps are uneven and material-specific, "nearest gauge" is a lookup, not a formula. The Reverse field does exactly that: type a thickness and it returns the closest gauge in the currently selected material, plus the signed percentage difference so you can judge the fit.

For example, 1.60 mm against the galvanized table lands on 16 ga (1.613 mm, +0.8 %) — an excellent match. The same 1.60 mm against the bare steel table lands between 16 ga (1.519 mm) and 15 ga (1.709 mm), nearest 16 ga at −5.1 %. This is the moment the material-specific tables earn their keep: the right answer depends on which metal you are holding.

Mill rolling tolerances also matter here. Sheet is delivered to a thickness band, not an exact number — typically a fraction of the nominal depending on width and the product standard — so a micrometer reading a few percent off the book value is normal and does not mean you have the wrong gauge.

Most of the world outside North America simply orders sheet by its metric thickness (0.8, 1.0, 1.2, 1.5, 2.0, 3.0 mm …), and modern drawings increasingly do the same even where gauge is spoken day to day. The reasons are practical:

1. No ambiguity. "1.5 mm CRS" means exactly one thing; "16 gauge" means four things depending on material and coating.
2. CAD and CAM want a number. Press-brake bend deductions, laser cut parameters and nesting all run on the decimal thickness — the gauge label is translated to it anyway.
3. Cross-material design. If you are substituting aluminum for steel to save weight, matching the thickness (for stiffness/handling) is a different decision from matching the gauge, and only the decimal makes that explicit.

The pragmatic workflow: think in gauge, buy in gauge, but dimension in mm or decimal inches. This tool is built for exactly that hand-off — pick the gauge you know, read the exact thickness and weight, and put the decimal on the drawing. Every value here is the published standard figure, so it matches your supplier's chart to the last digit.

A rough field guide to the gauges you will actually meet (steel thicknesses shown; remember the same number is thinner in aluminum, thicker in galvanized):

• 7–10 ga (4.6–3.4 mm): structural sheet, heavy brackets, trailer decks, wear plates, base plates for light framing.
• 11–14 ga (3.0–1.9 mm): machine guards, enclosures, shelving, heavier HVAC plenums, weldments that must not oil-can.
• 16 ga (1.52 mm): the workhorse — brackets, electrical boxes, automotive panels, general fabrication. The most-searched gauge for a reason.
• 18–20 ga (1.21–0.91 mm): appliance panels, HVAC ductwork, light enclosures, decorative stainless.
• 22–26 ga (0.76–0.45 mm): roofing and siding, flashing, residential ductwork, light galvanized work.
• 28–30 ga (0.38–0.30 mm): the thinnest common sheet — flashing, drip edge, economy roofing.

Because roofing and HVAC are so often galvanized, and architectural work so often stainless or aluminum, the "same gauge, different metal" trap shows up constantly on real jobs — one more reason to confirm the actual thickness here before you cut.