Sheet Metal Gauge Chart: Thickness in mm and Inches

A gauge number is not a measurement. It is a trade designation that maps to a different thickness for each material family, so 16 gauge steel, stainless and aluminum are three different sheets. The charts below give nominal thickness in inches and millimeters for carbon steel, galvanized, stainless and aluminum from 3 to 30 gauge, with weight per square foot. Use them to read a drawing, check a quote, or convert an old gauge callout.

What a Sheet Metal Gauge Chart Tells You

A gauge chart converts a gauge number into a nominal thickness for one material family. It defines no tolerance, alloy or finish. 16 gauge carbon steel is 0.0598 in (1.52 mm), 16 gauge stainless is 0.0625 in (1.59 mm), and 16 gauge aluminum is 0.0508 in (1.29 mm).

A chart reads a drawing; it does not place an order. Millimeters, a tolerance and a material standard control the part, because the mill ships inside a tolerance band set by ASTM, EN or GB. Gauge runs from 3 (6.07 mm) to 30 (0.30 mm); thicker stock is ordered as plate by decimal thickness, and thinner stock as foil.

Standard Steel Gauge Chart (3 to 30 Gauge)

In US Standard Gauge, the table used for carbon steel sheet in North America, 3 gauge is 0.2391 in (6.07 mm) and 30 gauge is 0.0120 in (0.30 mm). The sizes you will see most are 16 gauge at 0.0598 in (1.52 mm), 18 gauge at 0.0478 in (1.21 mm) and 20 gauge at 0.0359 in (0.91 mm).

Weights assume 0.2836 lb/in³ (7.85 g/cm³). 16 gauge is 1.519 mm, so a 1.5 mm drawing and 16 gauge are 0.02 mm apart, inside most mill tolerances.

Galvanized Steel Gauge Chart

Galvanized sheet has its own gauge progression because the zinc coating adds thickness. 16 gauge galvanized is nominally 0.0635 in (1.61 mm), roughly 0.004 in heavier than 16 gauge uncoated steel. 20 gauge is 0.0396 in (1.01 mm), 24 gauge is 0.0276 in (0.70 mm), and the standard numbers run from 8 to 30 gauge.

Two thicknesses are in play: the steel substrate and the coated overall thickness. ASTM A653 controls the product, ASTM A924 the general requirements, and coating class is separate (G60 to G300). G90 adds about 0.0015 in (0.04 mm), which is why 16 gauge is 0.0635 in rather than 0.0613 in. Order base metal plus coating class.

Stainless Steel Gauge Chart (ASTM A480)

Stainless sheet has a separate table, published through ASTM A480. 16 gauge stainless is 0.0625 in (1.59 mm), 18 gauge is 0.0500 in (1.27 mm), 20 gauge is 0.0375 in (0.95 mm), and 14 gauge is 0.0781 in (1.98 mm). A stainless callout read against a carbon steel chart lands about 4% low.

At the heavy end the table follows a fractional series (0.2500, 0.2344, 0.2187 in) rather than USS steps, so 3 gauge stainless is 0.2500 in against 0.2391 in for steel. Stainless work-hardens, so thickness drives bend radius and springback.

Aluminum Gauge Chart (Brown & Sharpe)

Aluminum sheet is gauged on Brown & Sharpe (B&S), which is thinner than steel at the same number. 16 gauge aluminum is 0.0508 in (1.29 mm), 20 gauge is 0.0320 in (0.81 mm), 12 gauge is 0.0808 in (2.05 mm), and 3 gauge is 0.2294 in (5.83 mm). B&S is also the sheet gauge for copper and brass.

ASTM B209 covers sheet from 0.006 to 0.249 in and plate from 0.250 in up, so 3 gauge aluminum is still sheet. Density varies by alloy: 3003 is about 2.73 g/cm³, 5052 about 2.68, 6061 about 2.70. Temper changes formability, not thickness.

Why a Higher Gauge Number Means Thinner Metal

Gauge numbering came from wire drawing, where each pass through a smaller die reduced the diameter and advanced the count. The scale was never designed as a measurement system, so the steps are uneven and were fixed by trade associations rather than arithmetic.

Birmingham gauge came from the 19th century wire trade, Brown & Sharpe was standardized in the 1850s, and US Standard Gauge was adopted by American steel producers later. The steps explain why no multiplier works: 13 to 14 gauge is 0.0150 in (0.38 mm), 16 to 17 gauge is 0.0060 in (0.15 mm), and a two gauge jump removes 0.0149 in near 16 gauge but 0.0299 in near 8 gauge.

Production splits by thickness: 24 to 30 gauge (0.61 to 0.30 mm) is normally blanked in a metal stamping die, 16 to 20 gauge is laser cut and formed, and 3 to 8 gauge is heavy fabrication.

Gauge Systems Compared: USS, Stainless, Brown & Sharpe and Metric

Four conventions cover most sheet metal orders: US Standard Gauge for carbon and galvanized steel, the stainless table in ASTM A480, Brown & Sharpe for aluminum, copper and brass, and straight millimeters under EN standards. The same number gives four different thicknesses, so the material decides which table applies.

Older UK drawings may carry Birmingham gauge (BG) or Standard Wire Gauge (SWG), which run heavier than USS at the same number; ask for the original standard or the decimal thickness. AWG is the wire version of Brown & Sharpe, so 16 AWG wire is 0.0508 in, the same as 16 gauge aluminum sheet; a wire gauge is still not a sheet callout.

Thickness Tolerances: ASTM A480, A924 and What They Permit

A gauge chart gives nominal thickness; the material standard gives the permitted variation around it. ASTM A480 covers stainless sheet, ASTM A924 covers hot-dip coated sheet including galvanized, and ASTM A1011, A1008 and B209 cover carbon and aluminum sheet. The permitted band widens as sheet gets thicker and wider.

For cold-rolled sheet between 0.5 and 2.0 mm the permitted band is usually ±0.03 to ±0.10 mm, set by thickness and width; on thin sheet it can approach the 0.15 mm step between 18 and 19 gauge. A480 and A924 tabulate these limits, and A924 controls coating weight separately.

Certificates report the heat and specification, not the thickness of every square meter. When thickness is critical, measure away from sheared edges, which are thinner and work-hardened. Incoming inspection and first-article reports are the proof.

How to Specify Sheet Thickness to a Fabricator

Specify the material and grade, the thickness with a tolerance, the material standard, the finish and the blank size. Never write only 16 gauge. If a legacy drawing uses gauge, add the decimal equivalent in brackets and state which table produced it.

A complete callout reads: 304L stainless steel sheet, 1.50 mm ±0.05 mm, ASTM A240/A480, 2B finish, 1219 × 2438 mm, laser cut and deburred, 25 pieces. The grade sets corrosion resistance and weldability, and thickness and tolerance set the inspection criterion.

Choose the direction deliberately: symmetric ± for fit, a minimum (1.50 mm min) when strength or corrosion allowance governs, a maximum when weight or clearance governs. A minimum is not nominal plus tolerance.

For coated sheet, state base metal and coating class separately, for example 0.048 in base metal, G90, ASTM A653, which settles whether the number includes zinc. Two questions belong in every RFQ: which gauge table do you use, and do you measure base metal or overall thickness? A sheet metal fabrication partner answers both.

Converting Gauge to mm: Formula and Worked Example

There is no formula from gauge number to thickness, because the table is a set of conventions with uneven steps. Conversion is a lookup plus one multiplication: read the inch value from the correct table, then multiply by 25.4. 16 gauge steel is 0.0598 in, so 0.0598 × 25.4 = 1.52 mm.

• millimeters = inches × 25.4
• inches = millimeters ÷ 25.4
• lb/ft² = thickness (in) × 40.8 steel, 41.8 stainless, 14.1 aluminum
• kg/m² = thickness (mm) × 7.85 steel, 8.0 stainless, 2.70 aluminum

Worked example. A drawing calls for 14 gauge 5052-H32 aluminum sheet, 48 × 96 in, 20 pieces.

1. The material is aluminum, so use Brown & Sharpe: 14 gauge is 0.0641 in.
2. Convert: 0.0641 × 25.4 = 1.628 mm. Specify 1.63 mm with the ASTM B209 tolerance for the ordered width.
3. Weight: 0.0641 × 14.1 = 0.90 lb/ft². At 32 ft² per sheet that is 28.9 lb (13.1 kg), or 578 lb for 20 sheets.
4. If the shop used the steel table, 14 gauge would be 0.0747 in (1.90 mm): 16.5% thicker, 33.7 lb per sheet, 58% stiffer in bending, and a different bend allowance.

A 2.0 mm drawing is 0.0787 in, between 13 gauge (0.0897 in) and 14 gauge (0.0747 in). No gauge equals 2.0 mm: 14 gauge is 1.90 mm, 5% thin, and ordering it as 14 gauge under-runs the design.

Actual thickness sets the process. Fiber laser cutting up to 20 mm holds a kerf of 0.1 to 0.3 mm on thin sheet, and thickness sets cut speed and edge quality. Bending is more sensitive: bend deduction moves with actual thickness, so a 4% error accumulates over every flange.

Sheet Weight per Square Foot and per Square Meter

Weight follows from thickness and density. Carbon steel is 40.8 lb/ft² per inch (7.85 kg/m² per mm), stainless 41.8 and 8.0, aluminum 14.1 and 2.70. A 1.5 mm steel sheet at 1219 × 2438 mm weighs 35.0 kg (77 lb).

The weight column is for checking quotes and freight. 16 gauge steel at 2.44 lb/ft² and 14 gauge at 3.05 lb/ft² differ by 25% in material cost for the same area, visible before anyone cuts metal. G90 adds about 0.056 lb/ft². Alloy density matters more on aluminum; grade data is on the materials page.

FAQ: Sheet Metal Gauge Questions

What is 16 gauge sheet metal in mm?

It depends on the material. 16 gauge carbon steel is 0.0598 in (1.52 mm), galvanized about 0.0635 in (1.61 mm), stainless 0.0625 in (1.59 mm), aluminum 0.0508 in (1.29 mm) on Brown & Sharpe. Check the material before you convert the number.

Is 16 gauge thicker than 18 gauge?

Yes. Lower gauge numbers are thicker in every sheet gauge system. 16 gauge carbon steel is 0.0598 in (1.52 mm) and 18 gauge is 0.0478 in (1.21 mm), so 16 gauge is about 25% thicker. The same direction applies to stainless and aluminum.

Why is 16 gauge aluminum thinner than 16 gauge steel?

Aluminum uses Brown & Sharpe, a table built for non-ferrous metals, while steel uses US Standard Gauge. Different trades fixed the two, so the same number lands on different thicknesses. 16 gauge aluminum is 1.29 mm against 1.52 mm, about 15% thinner.

Can I specify gauge on a tolerance-critical drawing?

No. A gauge number is a nominal trade designation with no tolerance attached, and suppliers may use different tables for the same material. Specify millimeters or decimal inches plus a tolerance and the material standard, such as 1.50 mm ±0.05 mm to ASTM A480.

How do I convert gauge to millimeters?

Look up the inch value for the material in the correct table, then multiply by 25.4. For example, 14 gauge carbon steel is 0.0747 in, and 0.0747 × 25.4 = 1.90 mm. There is no direct formula because the gauge steps are not uniform.

Getting the Thickness Right on Your Next Order

Send a drawing with a millimeter thickness, a tolerance and the material standard, and the fabricator can hold it. YC Prime Precision laser cuts sheet to 20 mm, press-brakes to 6 m at ±0.1 mm, and stamps from 0.1 to 6 mm in a 90,000 m² plant in Qingdao, Shandong.

Sheet metal orders ship 5 to 12 business days after drawing approval. Gauge also limits finishing: thin sheet distorts at cure temperature, so check powder coating cure schedules and film thickness before specifying 24 gauge. If your drawing still says 16 gauge, send it as it is and we will confirm the table, the decimal and the tolerance before quoting. Start with an instant quote.