Fabrication Reference
Sheet Metal Gauge to mm and inches (Thickness Conversion)
A sheet-metal gauge has no single universal thickness. Select the material and gauge system before reading its millimeter or inch thickness.
Maintained by mmtoinches.im · Updated
NIST describes the standard inch as exactly equivalent to 25.4 mm
. NIST length definition. OnlineMetals — material-specific gauge chart. Method and limitations.
Convert sheet metal gauge numbers to thickness for steel, galvanized steel, and aluminum. Use the tables to see nominal thicknesses in inches and millimeters, and pick the right material thickness for your project.
Conversion basics
mm = inches × 25.4
inches = mm ÷ 25.4
Gauge values come from material-specific charts. Do not mix steel, galvanized, and aluminum tables.
Need precise conversions?
Use the mm to inches converter for arbitrary thicknesses, then reference the gauge tables to align with stocked sheet sizes.
Reverse lookup — find gauge from thickness
Enter a thickness to see suggested gauge in the selected material.
Nominal values only. Coatings and mill tolerances apply; verify with supplier datasheets.
Weight per area estimator
Densities: steel/galvanized ≈ 7850 kg/m³; aluminum ≈ 2700 kg/m³Using thickness: — enter thickness above
Material: Steel
kg/m²: —
lb/ft²: —
Nominal estimates; coatings and alloy variations affect density and thickness.
Steel gauge chart (nominal thickness)
Nominal thickness. Values shown to 4 decimals (in) and 2 decimals (mm).
| Gauge | Thickness (in) | Thickness (mm) |
|---|---|---|
| 3 | 0.2391 | 6.07 |
| 4 | 0.2242 | 5.69 |
| 5 | 0.2092 | 5.31 |
| 6 | 0.1943 | 4.94 |
| 7 | 0.1793 | 4.55 |
| 8 | 0.1644 | 4.18 |
| 9 | 0.1495 | 3.80 |
| 10 | 0.1345 | 3.42 |
| 11 | 0.1196 | 3.04 |
| 12 | 0.1046 | 2.66 |
| 13 | 0.0897 | 2.28 |
| 14 | 0.0747 | 1.90 |
| 15 | 0.0673 | 1.71 |
| 16 | 0.0598 | 1.52 |
| 17 | 0.0538 | 1.37 |
| 18 | 0.0478 | 1.21 |
| 19 | 0.0418 | 1.06 |
| 20 | 0.0359 | 0.91 |
| 21 | 0.0329 | 0.84 |
| 22 | 0.0299 | 0.76 |
| 23 | 0.0269 | 0.68 |
| 24 | 0.0239 | 0.61 |
| 25 | 0.0209 | 0.53 |
| 26 | 0.0179 | 0.45 |
| 27 | 0.0164 | 0.42 |
| 28 | 0.0149 | 0.38 |
| 29 | 0.0135 | 0.34 |
| 30 | 0.0120 | 0.30 |
| 31 | 0.0109 | 0.28 |
| 32 | 0.0097 | 0.25 |
| 33 | 0.0086 | 0.22 |
| 34 | 0.0076 | 0.19 |
| 35 | 0.0067 | 0.17 |
| 36 | 0.0058 | 0.15 |
Data sources and version: see “Standards & Sources” below. Last updated 2025-11-25.
Practical guidance
- Round inches to 4 decimals and mm to 2 decimals for spec sheets; keep more precision in CAD.
- Coatings and galvanization add thickness; confirm with supplier tolerances for critical bends and fits.
- For HVAC, enclosures, and panels, check rigidity and weight alongside thickness when selecting gauge.
- Document the material and gauge system in drawings to avoid substituting a different chart.
Application scenarios — recommended gauges
- HVAC ductwork: typical 26–24 ga (regional standards apply).
- Enclosures and electrical cabinets: typical 16–18 ga (balance structural strength and weight).
- Automotive body panels: typical 20–22 ga.
- Decorative panels: typical 22–24 ga.
Notes
- Weight and rigidity: consider panel size, reinforcement, and mounting.
- Bend radius: check tooling and alloy; thin sheets may wrinkle, thick sheets may crack.
- Coating impact: galvanization or paint adds thickness; confirm base sheet thickness separately.
Standards & Sources
Gauge numbers for sheet metal are table-driven and differ by material. Values shown are nominal and widely used for industry reference. Always verify with supplier datasheets and applicable specifications when tolerances matter.
- Steel (plain) & Galvanized: Based on Manufacturers' Standard Gauge (MSG). See supplier charts and ASTM references. Examples: OnlineMetals gauge chart,Engineering Toolbox.
- Aluminum: Common charts align to the Brown & Sharpe tradition for non‑ferrous sheet. See supplier references such asOnlineMetals andEngineering Toolbox.
- Background: Sheet metal — gauge explains gauge systems and material differences. For a deeper dive, see Gauge systems explained.
Note: Galvanized thickness can include zinc coating; nominal gauge values are for base sheet and may vary by coating specification.
Frequently Asked Questions
Gauge systems are material-specific. Standards define different nominal thickness per gauge for steel, galvanized steel, and aluminum. Use the correct chart for your material to avoid under- or over-thickness.
No. Gauge numbers are table-driven, not a single formula. Use material-specific charts and convert inches to mm using 25.4 when needed.
Charts list nominal thickness. Actual sheets vary by mill tolerances and coatings. Verify with supplier datasheets and measure critical parts with calipers or micrometers.
Use the reverse lookup card: enter mm or inches, choose the material, and it returns the closest gauge with neighbors for context. Gauge-to-thickness mappings differ by material, so always pick the correct chart.
Yes—zinc coating adds thickness. Specify base sheet gauge separately from coating (e.g., “14 ga galvanized per ASTM A653, Z180”), and confirm tolerances with the supplier for bends and fit-up.
Gauge systems are historically table-driven and material-specific. Different charts and revisions may show small differences. Reference the correct chart for your material and cite the source in documentation.
Enable fraction display and choose a denominator (1/16, 1/32, 1/64). Fractions are rounded; note the tolerance is about ± 1/(2×denominator) inch. Always pair fractions with exact decimals in specs.
Specify sheet thickness with confidence
Use the material-specific gauge charts, then cite both inches and millimeters on drawings to prevent fabrication surprises.
Sources and calculation notes
A sheet-metal gauge has no single universal thickness. Select the material and gauge system before reading its millimeter or inch thickness.
Method: Look up the selected material-specific gauge thickness first, then convert mm and inches using 25.4. Do not use an AWG wire-diameter formula for sheet metal.
Scope: Listed thicknesses are reference values, not a tolerance specification. Confirm the actual material, applicable standard, thickness and tolerance with your supplier.
Content maintained by mmtoinches.im. Updated and reference notes reviewed . How we calculate and present measurements. Sources support the stated definitions; examples and calculators are not certification of a product or compliance with a standard.