Gauge to mm and inches: sheet metal thickness chart

A gauge number is not a thickness until you know the metal. This chart gives gauges 3 to 30 in inches and millimetres for the four scales in use — carbon steel, galvanized steel, stainless steel and aluminium (US: aluminum) — with the weight of steel sheet per square foot and per square metre.

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Short answer

• 10 gauge steel — 0.1345 in, 3.42 mm.
• 12 gauge steel — 0.1046 in, 2.66 mm.
• 14 gauge steel — 0.0747 in, 1.90 mm.
• 16 gauge steel — 0.0598 in, 1.52 mm.
• 18 gauge steel — 0.0478 in, 1.21 mm.
• 20 gauge steel — 0.0359 in, 0.912 mm.

The same numbers in stainless steel and aluminium are different thicknesses — see the columns below before ordering or setting a machine.

Gauge chart for steel, galvanized, stainless and aluminium

Steel is listed from 3 gauge, galvanized from 8, stainless from 7 and aluminium from 6: thicker material is usually ordered as plate, by fractional or decimal thickness. The galvanized figures include the zinc coating, which is why they run about 0.004 in above bare steel of the same gauge.

Weight of steel sheet by gauge

The “nominal” column is the weight the scale itself assigns. The Manufacturers’ Standard Gauge was built on weight, at 41.82 lb per square foot for every inch of thickness, and the thicknesses were derived from it. The “calculated” columns take the thickness in the chart and the density of steel, 7.85 g/cm³. They come out 2.3 % lighter at every gauge; for a bill of materials use the calculated figure or the sheet metal weight calculator, which takes any size and any metal.

From millimetres to the nearest gauge

No gauge lands exactly on a round metric thickness. A drawing that calls for 1.5 mm steel gets 16 gauge (1.52 mm) in a US shop, and 2 mm becomes 14 gauge (1.90 mm) — five per cent thinner than drawn. Where the thickness carries load or sets a fit, state it in millimetres and let the supplier quote the nearest stock size.

Four scales, one set of numbers

• Carbon steel — Manufacturers’ Standard Gauge (MSG). Uncoated hot- and cold-rolled sheet. Defined by weight; 16 gauge is 40 oz/ft².
• Galvanized steel. The same base scale plus the coating, so each gauge is a little thicker than bare steel.
• Stainless steel — U.S. Standard Gauge. The 1893 scale of exact fractions: 16 gauge is 1/16 in, 11 gauge is 1/8 in.
• Aluminium, brass, copper — Brown & Sharpe. The American Wire Gauge progression applied to sheet. Noticeably thinner than steel at the same number: 16 gauge is 1.29 mm against 1.52 mm.

Current ASTM specifications do not work in gauges: they give a decimal thickness and a tolerance, and the gauge survives as a trade name. That is why a mill test report shows a thickness, not a gauge.

What the gauge means at the welding machine

Settings charts on US welders are laid out by gauge, so the conversion is the first step in setting up. At 18 gauge (1.21 mm) and thinner, burn-through and distortion decide the technique more than strength does; the settings and the sequence that keep thin panels flat are in welding thin sheet. Starting values for wire feed, voltage and gas by thickness are in the MIG and TIG settings chart — look them up by the millimetre figure from the chart above.

For the other US units on a machine or a procedure sheet — inches per minute, cubic feet per hour, ksi — use the welding unit converter.

Author: Dmitry Frolov, welder and metal fabricator Updated: 13 October 2026