3 Gauge Sheet Metal

Steel (MSG) 0.2391″
Galvanized
Stainless 0.2500″
Aluminum 0.2294″

Steel: 6.07 mm · Stainless: 6.35 mm · Aluminum: 5.83 mm . The same gauge number is a different thickness in each material — always confirm which scale a drawing means, or better, specify decimal thickness.

Neighboring gauges (steel column)

Gauge Steel Galvanized Stainless Aluminum
3 0.2391 0.2500 0.2294
4 0.2242 0.2344 0.2043
5 0.2092 0.2187 0.1819

Measuring wire, not sheet? Wire uses the AWG scale — see AWG 3 (0.2294″ Ø). Aluminum sheet happens to share the AWG scale, which is why the aluminum column matches it.

Data provenance. Sheet-metal gauge tables: Manufacturers’ Standard Gauge (steel), galvanized, and stainless (Industry reference). ASTM B258, Standard Specification for Nominal Diameters of AWG Sizes (ASTM International). Steel per Manufacturers' Standard Gauge; stainless per the conventional supplier table (no governing standard); aluminum per B&S (= AWG, ASTM B258). Sheets carry rolling tolerances. See all data sources.