Sheet Metal Gauge Chart: Steel, Galvanized, Stainless, Aluminum

mm and inch thickness for every gauge number, why aluminum is not steel, and how to stop ordering the wrong sheet.

1. What gauge actually means

Gauge is a thickness number inherited from the old wire-drawing tradition: it counted how many passes a wire took through a draw plate. For sheet metal the rule is the opposite of what intuition suggests — a HIGHER gauge means a THINNER sheet. In the US, the Manufacturers' Standard Gauge (MSG) system is defined by weight, not by direct measurement: 41.82 lb per square foot for every inch of thickness, so steel gauge numbers trace back to a weight-based scale.

2. The chart: gauge to mm by material

Thickness in millimeters by material — same gauge number, four different sheets:

Gauge	Steel	Galvanized	Stainless	Aluminum
10	3.42	3.51	3.57	2.59
12	2.66	2.75	2.78	2.05
14	1.90	1.99	1.98	1.63
16	1.52	1.61	1.59	1.29
18	1.21	1.31	1.27	1.02
20	0.91	1.01	0.95	0.81
22	0.76	0.85	0.79	0.64
24	0.61	0.70	0.64	0.51

(all values in mm)

3. Steel sheet gauge chart: mm, inches, kg/m²

Manufacturer's Standard Gauge for plain sheet steel; weight at 7.85 kg per m² per mm:

Gauge	mm	inch	kg/m²
6	4.94	0.1943	38.8
7	4.55	0.1793	35.7
8	4.18	0.1644	32.8
9	3.80	0.1495	29.8
10	3.42	0.1345	26.8
11	3.04	0.1196	23.8
12	2.66	0.1046	20.8
13	2.28	0.0897	17.9
14	1.90	0.0747	14.9
15	1.71	0.0673	13.4
16	1.52	0.0598	11.9
17	1.37	0.0538	10.7
18	1.21	0.0478	9.5
19	1.06	0.0418	8.3
20	0.91	0.0359	7.2
21	0.84	0.0329	6.6
22	0.76	0.0299	6.0
23	0.68	0.0269	5.4
24	0.61	0.0239	4.8
25	0.53	0.0209	4.2
26	0.46	0.0179	3.6
27	0.42	0.0164	3.3
28	0.38	0.0149	3.0
29	0.34	0.0135	2.7
30	0.30	0.0120	2.4
31	0.27	0.0105	2.1
32	0.25	0.0097	1.9
33	0.23	0.0090	1.8
34	0.21	0.0082	1.6

4. Galvanized sheet: why the numbers shift

Galvanised sheet has its own standard because the zinc coating counts toward the gauge: 16 gauge galvanized is 1.61 mm against 1.52 mm for plain steel; 20 gauge is 1.01 mm against 0.91 mm.

Gauge	mm	inch
8	4.27	0.1680
10	3.51	0.1382
12	2.75	0.1084
14	1.99	0.0785
16	1.61	0.0635
18	1.31	0.0516
20	1.01	0.0396
22	0.85	0.0336
24	0.70	0.0276
26	0.55	0.0217
28	0.48	0.0187

Aluminium uses yet another system (Brown & Sharpe): 16 gauge aluminium is 1.29 mm, 14 gauge 1.63 mm, 20 gauge 0.81 mm. When a drawing says 16 gauge, ask which material — the word alone is ambiguous.

5. The costly mistake: gauge is not a material

Gauge alone does not define a thickness — it only means something together with the material. 16 gauge steel is 1.52 mm, but 16 gauge aluminum is only 1.29 mm, about 15% thinner. A classic HVAC story: a shop orders 16 ga sheet for ductwork, receives aluminum instead of steel, and the whole run comes out floppy and out of spec. Always specify material AND thickness in mm — "1.5 mm galvanized steel", never just "16 gauge".

6. Gauge vs AWG vs SWG

Three different gauge systems are often confused. Sheet metal uses the Manufacturers' Standard Gauge; AWG (American Wire Gauge) sizes electrical wire; SWG (Imperial Standard Wire Gauge) is the old British standard. A 16 AWG wire and a 16 gauge sheet have nothing in common. ASTM A480, the standard for stainless sheet, explicitly discourages gauge numbers and calls the term archaic — order by decimal inch or mm.

7. 15/10ème, chapa 16 and other local conventions

Not every country speaks gauge. France often states thickness in tenths of a millimetre: 15/10ème is 1.5 mm, 20/10ème is 2.0 mm. Brazil and Portugal use the chapa number — chapa 16 is about 1.5 mm of black steel sheet, close to 16 gauge steel but a different standard, so convert rather than assume. Germany and most of Europe state millimetres outright. Anchor points:

Convention	Meaning	mm
10/10ème	One millimetre	1.0
15/10ème · chapa 16 · 16 gauge steel	General-purpose sheet	1.5
20/10ème	Two millimetres	2.0
25/10ème	Light plate	2.5

8. A practical workflow

Measure the old sheet with a caliper in mm, order in mm, and convert back to gauge only when an older spec sheet forces you to. When in doubt, write both on the order: gauge for the shop floor, mm for the invoice. The Sheet metal gauge converts both ways for steel, galvanized, stainless and aluminum and adds sheet weight, so quotes and orders always match.

9. How thick is…? Gauge quick answers

The gauge questions asked most, answered in one place: 16 gauge steel is 1.52 mm (0.0598 in); 14 gauge 1.90 mm; 12 gauge 2.66 mm; 10 gauge 3.42 mm; 18 gauge 1.21 mm; 20 gauge 0.91 mm; 22 gauge 0.76 mm; 24 gauge 0.61 mm; 26 gauge 0.46 mm. All values are plain sheet steel: galvanized runs 0.05–0.10 mm thicker at the same gauge, aluminium follows a different standard.

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