Sheet Metal Gauge Chart: Gauge to mm and Inches

What is sheet metal gauge?

Gauge (also spelled gage) is the traditional way to state the thickness of sheet metal. Each gauge number stands for a fixed thickness in its material’s system, so a drawing that says “16 GA” on a steel part means 0.0598 in (1.52 mm). The number is a label, not a measurement: it has no unit of its own.

Four systems are in everyday use. Uncoated steel follows the Manufacturers’ Standard Gauge, galvanized steel the Galvanized Sheet Gauge, stainless the US Standard Gauge, and aluminum, brass and copper the Brown & Sharpe gauge. The same gauge number gives a different thickness in each, which is why a gauge callout always needs the material beside it.

How thick is 14 gauge steel?

14 gauge steel is 0.0747 in (1.90 mm). The other gauges people look up most are 16 gauge at 0.0598 in (1.52 mm), 11 gauge at 0.1196 in (3.04 mm), 12 gauge at 0.1046 in (2.66 mm) and 10 gauge at 0.1345 in (3.42 mm). All of these are the standard gauge for uncoated carbon steel sheet.

The weight column is the definition: the steel gauge was set by weight per square foot, and the thickness follows from it at 41.82 lb per square foot per inch. Galvanized sheet of the same gauge runs about 0.004 in thicker, because the zinc coating is counted.

What does a sheet metal gauge chart look like?

The full chart gives each gauge in inches and millimetres for the four systems, written as inches / mm. A dash means that system does not define the gauge: galvanized sheet runs from 8 to 32 gauge, stainless from 7 to 36, steel from 3 to 38, and aluminum from 0 to 36.

Aluminum gauges 0, 1 and 2 (0.3249 in (8.25 mm), 0.2893 in (7.35 mm) and 0.2576 in (6.54 mm)) sit above the chart; in practice aluminum that thick is sold as plate by its decimal thickness.

How do I convert gauge to mm or inches?

Look the gauge up in its material’s column, or use the converter at the top of the page. For steel the thickness in inches is the weight in pounds per square foot divided by 41.82, and millimetres are inches multiplied by 25.4: 16 gauge is 2.5 ÷ 41.82 = 0.0598 in, and 0.0598 × 25.4 = 1.52 mm.

Going the other way, from a metric thickness to a gauge, there is rarely an exact match. 2 mm steel sits between 14 gauge (1.90 mm) and 12 gauge (2.66 mm), and 1 mm between 20 gauge (0.91 mm) and 19 gauge (1.06 mm). Metric sheet is ordered and drawn by its thickness in millimetres, so a metric drawing shows no gauge at all.

Why is a higher gauge number thinner?

The numbers come from wire drawing, where the gauge counted how many times the wire had been pulled through a die; more passes meant a thinner wire. Sheet makers kept the convention, so 30 gauge is thin and 3 gauge is nearly a quarter inch. Each step is a roughly constant ratio, not a constant amount.

In the aluminum system the ratio is exact: every gauge is about 11% thinner than the one before, and six gauges halve the thickness. The steel gauge steps are rounder weights, which is why its chart has odd-looking decimals.

Why do steel, stainless and aluminum gauges differ?

Each industry fixed its own table before anyone agreed on one. Steel went by weight per square foot, stainless by fractions of an inch, and the non-ferrous metals by their wire gauge. So 16 gauge is 0.0598 in (1.52 mm) in steel, 0.0625 in (1.59 mm) in stainless and 0.0508 in (1.29 mm) in aluminum.

Galvanized steel adds a fourth table because its gauge includes the zinc coating: 16 gauge galvanized is 0.0635 in (1.61 mm). When a drawing gives a gauge without a material, assume uncoated steel only if the title block or the material note says steel; otherwise ask.

How is sheet thickness called out on a drawing?

A sheet metal drawing gives the thickness in the material note or the title block, as a gauge with the material (“16 GA CRS”, “MATL: 14 GA HRPO”) or as a decimal (“0.060 AL 5052-H32”, “1.5 mm”). Newer prints prefer the decimal because it is unambiguous; older prints lean on the gauge.

The thickness feeds everything else on a sheet metal part: the bend radius, the bend allowance and the flat pattern all depend on it. For flat lengths and K-factors see the bend allowance calculator, and for the other notes on the sheet see engineering drawing symbols. A 3D model needs a real thickness, so a gauge on the print becomes the decimal from this chart in the CAD.

Frequently asked questions

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