Gauge reference · mm and inches · Updated July 2026
Standard Metal Thickness Chart: Gauge to mm & Inches
A gauge number is incomplete without the material and gauge system. Sixteen-gauge standard steel is about 1.519 mm, common 16-gauge stainless is 1.588 mm, and a legacy Brown & Sharpe nonferrous reference gives 1.290 mm. Use the correct column—and specify decimal thickness on drawings and purchase orders.
Photo: Sunnybansodeva, CC BY-SA 4.0 via Wikimedia Commons.
The short answer
Read a metal thickness chart in four steps
Gauge is a lookup system, not a universal formula. The same number can represent different thicknesses, and the received sheet can legitimately vary around its nominal value.
Carbon steel, stainless, coated steel and nonferrous sheet do not share one reliable gauge-to-thickness column.
Use U.S. Standard Gauge for iron and steel, a stated stainless convention or a specifically agreed nonferrous reference.
Use 1 inch = 25.4 mm exactly. Keep enough decimal places for design, then round only for communication.
Nominal chart thickness is not the acceptance range. Apply the product specification, width, alloy, temper and coating requirements.
How to use this reference
What does a metal gauge number actually tell you?
For common sheet-metal gauge systems, a larger number means a thinner sheet. The sequence is not a linear thickness scale: the difference between adjacent numbers changes across the chart.
The U.S. statutory gauge for sheet and plate iron and steel is historically tied to both approximate thickness and weight per area. Stainless and nonferrous supplier tables developed through different conventions. That is why “18 gauge” by itself is not a complete material specification.
Write the alloy or grade, product form, nominal decimal thickness, unit system, governing specification and required tolerance. Add the gauge only as a convenient secondary reference.
Interactive lookup
Metal gauge-to-thickness finder
Select a material convention and gauge number. The tool returns nominal thickness, approximate mass per square meter and a safer purchase-order description.
Choose the reference
These are planning values. Supplier certificates and the applicable product standard control acceptance.
16 gauge standard steel
U.S. Standard Gauge lists a nominal thickness of 0.0598 inch for 16-gauge sheet steel. The metric value below uses the exact 25.4 mm/in conversion.
Gauge identifies a nominal reference. It does not establish alloy, finish, tolerance, flatness or mechanical properties.
Complete reference chart
Standard metal thickness chart from 7 to 30 gauge
The standard-steel column follows 15 U.S.C. §206. Stainless values are a common North American supplier convention rather than a claim that every stainless product specification uses gauge. The nonferrous column is the legacy Brown & Sharpe sheet reference commonly reproduced for aluminum, brass and copper; specify those materials by decimal thickness.
| Gauge | Standard steel (in) | Standard steel (mm) | Stainless (in) | Stainless (mm) | Legacy nonferrous (in) | Legacy nonferrous (mm) |
|---|---|---|---|---|---|---|
| 7 | 0.1793 | 4.554 | 0.1875 | 4.763 | 0.1443 | 3.665 |
| 8 | 0.1644 | 4.176 | 0.1719 | 4.366 | 0.1285 | 3.264 |
| 9 | 0.1495 | 3.797 | 0.1563 | 3.969 | 0.1144 | 2.906 |
| 10 | 0.1345 | 3.416 | 0.1406 | 3.572 | 0.1019 | 2.588 |
| 11 | 0.1196 | 3.038 | 0.1250 | 3.175 | 0.0907 | 2.304 |
| 12 | 0.1046 | 2.657 | 0.1094 | 2.778 | 0.0808 | 2.052 |
| 13 | 0.0897 | 2.278 | 0.0938 | 2.381 | 0.0720 | 1.829 |
| 14 | 0.0747 | 1.897 | 0.0781 | 1.984 | 0.0641 | 1.628 |
| 15 | 0.0673 | 1.709 | 0.0703 | 1.786 | 0.0571 | 1.450 |
| 16 | 0.0598 | 1.519 | 0.0625 | 1.588 | 0.0508 | 1.290 |
| 17 | 0.0538 | 1.367 | 0.0563 | 1.429 | 0.0453 | 1.151 |
| 18 | 0.0478 | 1.214 | 0.0500 | 1.270 | 0.0403 | 1.024 |
| 19 | 0.0418 | 1.062 | 0.0438 | 1.111 | 0.0359 | 0.912 |
| 20 | 0.0359 | 0.912 | 0.0375 | 0.953 | 0.0320 | 0.813 |
| 21 | 0.0329 | 0.836 | 0.0344 | 0.873 | 0.0285 | 0.724 |
| 22 | 0.0299 | 0.759 | 0.0313 | 0.794 | 0.0253 | 0.643 |
| 23 | 0.0269 | 0.683 | 0.0281 | 0.714 | 0.0226 | 0.574 |
| 24 | 0.0239 | 0.607 | 0.0250 | 0.635 | 0.0201 | 0.511 |
| 25 | 0.0209 | 0.531 | 0.0219 | 0.556 | 0.0179 | 0.455 |
| 26 | 0.0179 | 0.455 | 0.0188 | 0.476 | 0.0159 | 0.404 |
| 27 | 0.0164 | 0.417 | 0.0172 | 0.437 | 0.0142 | 0.361 |
| 28 | 0.0149 | 0.378 | 0.0156 | 0.397 | 0.0126 | 0.320 |
| 29 | 0.0135 | 0.343 | 0.0141 | 0.357 | 0.0113 | 0.287 |
| 30 | 0.0120 | 0.305 | 0.0125 | 0.318 | 0.0100 | 0.254 |
Values are nominal references, rounded to practical display precision. The exact inch-to-millimeter conversion factor is 25.4. Do not use this table as a material certificate or tolerance table.
Why the columns disagree
The same gauge number can mean three different thicknesses
The gauge number is an index into a particular table. It is not a physical unit such as a millimeter. If the buyer and supplier consult different tables, both can believe they fulfilled “16 gauge” while shipping different thicknesses.
0.0598 in / 1.519 mm under the U.S. Standard Gauge iron-and-steel table.
0.0625 in / 1.588 mm in a commonly used U.S. stainless supplier convention.
0.0508 in / 1.290 mm under the legacy Brown & Sharpe reference often reproduced for aluminum, brass and copper.
That difference changes mass, stiffness, bend deduction, slot fit, heat input and weld gap. The safest drawing therefore makes decimal thickness primary and treats gauge as secondary information.
Standards map
Which standard controls metal thickness?
A chart supplies nominal reference values. Product specifications determine chemistry, properties, dimensional tolerances and test requirements.
15 U.S.C. §206
Establishes the U.S. standard gauge table for sheet and plate iron and steel, including approximate inch, millimeter and weight-per-area values.
ASTM A568/A568M
Provides general requirements for hot- and cold-rolled carbon, structural and HSLA sheet, including applicable dimensional tolerance frameworks.
ASTM A480/A480M
Provides general requirements for flat-rolled stainless and heat-resisting steel. Product specifications such as ASTM A240/A240M may also apply.
ASTM B209/B209M
Covers aluminum-alloy sheet and plate by alloy, temper and decimal thickness; Aluminum Association H35.2/H35.2M addresses dimensional tolerances.
Do not combine inch-pound and SI tolerance tables casually
ASTM A480/A480M explicitly treats the inch-pound and SI systems separately; bracketed values are not always exact equivalents for conformance. Put the intended specification system on the order.
Material-specific interpretation
Steel and stainless: similar labels, different references
The steel values in the full chart have a statutory U.S. reference. Stainless “gauge” values remain common in catalogs and fabrication conversations, but the purchase order should identify decimal thickness and the governing stainless product specification.
Carbon steel
Use the standard-steel gauge chart as a nominal cross-reference. Then apply the actual hot-rolled, cold-rolled, structural or HSLA product specification and its tolerances.
Stainless steel
State alloy, finish and thickness—for example, 304 stainless sheet, No. 4 finish, 1.50 mm nominal—rather than assuming “16 gauge stainless” is a complete global specification.
Plate boundary
“Sheet” versus “plate” definitions vary with the product standard and industry. Do not use an arbitrary gauge cutoff when a specification defines the product form.
Mass calculations
Weight per area depends on actual thickness and density. A chart-based estimate is useful for quoting, but certified weight and measured thickness control receiving decisions.
Finish and coating
Paint, plating, polymer film and metallic coating can increase caliper thickness without changing the nominal base-metal designation.
International drawings
Metric drawings should state millimeters directly. Sending only a North American gauge number to a global supplier creates unnecessary interpretation risk.
Galvanized steel
Base-metal thickness and coated thickness are not the same
A metallic-coating designation describes coating mass on both sides, while the substrate has its own nominal thickness and tolerance. A handheld micrometer reads the combined caliper of steel plus coating.
GalvInfo’s technical reference gives the following nominal total-both-sides zinc thicknesses for common designations. These are useful estimates, not receiving limits for an individual point measurement.
Nominal zinc thickness added across both faces.
Nominal zinc thickness added across both faces.
Nominal zinc thickness added across both faces.
Nominal zinc thickness added across both faces.
Example: 20-gauge base steel with G90 coating
The standard-steel chart gives 0.912 mm nominal base thickness. Adding 0.0413 mm nominal total coating gives an illustrative combined caliper of about 0.953 mm. Actual point readings vary with substrate tolerance, coating distribution and measurement method.
Specify the coating designation
“22-gauge galvanized” does not state whether corrosion protection is G30, G60, G90 or another coating class. A complete order names the base product, grade, nominal thickness, ASTM A653/A653M coating designation and required dimensions.
For dimensional fit, decide whether the engineering dimension applies to the base metal or the final coated surface. For corrosion performance, coating mass and environment matter more than the visual brightness of the sheet.
Aluminum and other nonferrous sheet
Use decimal thickness as the primary specification
Many online charts place aluminum under Brown & Sharpe or AWG-style gauge values. Those values are useful for interpreting legacy shorthand, but ASTM B209/B209M and Aluminum Association dimensional standards specify flat products through alloy, temper and decimal thickness—not a universal aluminum-sheet gauge.
Commonly stocked nominal decimal sizes include:
Replacing 16-gauge steel with “16-gauge aluminum” changes both thickness and elastic modulus. Equal gauge, equal thickness and equal stiffness are three different assumptions—and none is automatically valid.
Nominal is not actual
Gauge conversion and thickness tolerance answer different questions
The chart answers: “What nominal decimal thickness is associated with this gauge reference?”
The tolerance standard answers: “What measured range is acceptable for this ordered product?”
The acceptance range can depend on nominal thickness, product width, product form, alloy, temper, edge distance, coating and whether the order uses inch-pound or SI provisions.
Nominal thickness and the intended unit system.
Alloy or grade, temper where applicable, finish and coating.
The ASTM, EN, JIS or other specification governing the order.
Default, restricted or specially negotiated thickness limits.
Instrument, location, surface condition and coating treatment.
Mill test report or certificate of conformance matched to the heat or coil.
Receiving inspection
How to measure sheet-metal thickness reliably
A chart tells you the nominal target. Measurement tells you what arrived. For thin sheet and tolerance decisions, an outside micrometer generally provides better control than a ruler or a slotted gauge tool.
Identify the applicable standard, tolerance, measurement locations and whether coating is included.
Remove dirt and burr interference; verify zero and use an instrument with suitable resolution and calibration status.
A ratchet or friction thimble helps prevent operator force from changing the reading, especially on softer or very thin stock.
Do not invent a universal edge distance or sample count. Follow the material specification and quality plan.
Log coil or heat, sheet location, coating state, instrument ID, reading and acceptance decision.
Selection examples
How to choose thickness for a real project
Application tables can suggest a starting range, but structure, pressure, span, fastener spacing, impact, vibration, corrosion and code requirements determine the final thickness.
Panels and cabinets
Consider door size, unsupported span, hardware load, impact resistance, grounding provisions, gasket compression and finish. A large door may need formed returns or reinforcement rather than simply thicker sheet.
Ductwork
Minimum metal thickness depends on duct dimensions, pressure class, reinforcement and the governing construction standard. Do not choose from a generic “22–26 gauge” rule.
Body and brackets
Formability, crash function, fatigue, corrosion protection and joining method matter. Modern vehicle sheet selection is grade- and function-specific.
Panels and flashing
Wind uplift, clip spacing, panel profile, substrate, coating and local building requirements control. “Gauge” claims can differ between nominal and minimum thickness marketing.
Brackets and frames
Evaluate load path, bend geometry, hole-edge distance, weld size, distortion and process availability. Geometry can improve stiffness more efficiently than thickness alone.
Trim and signage
Flatness, surface quality, handling damage and forming often dominate structural strength. A protective film can also affect measured caliper and tooling setup.
Fabrication impact
Why a 0.1 mm thickness error matters in production
Thickness enters machine setup, tooling geometry and quality acceptance. A chart-selection error can propagate through the whole routing.
Focus, speed and kerf
Material thickness changes required energy, focal strategy, gas behavior and achievable speed. Coating and alloy identity further change the process window.
Tooling and bend deduction
Thickness influences die opening, inside radius, tonnage, neutral-axis behavior and flat-pattern compensation. Use measured production data for tight work.
Heat input and fit-up
Thin sheet is more sensitive to gap, burn-through and distortion. A wrong gauge conversion can invalidate the parameter starting point and joint fit.
Tabs, slots and fasteners
Actual caliper affects press fits, clinching, rivet grip, thread engagement and stack height. Include coating and finish where the final interface requires it.
Do not use gauge alone to set cutting or welding parameters. Confirm material grade, finish, coating, measured thickness, joint geometry and the specific machine configuration.
Procurement checklist
Turn the chart result into an unambiguous RFQ
A strong request for quotation describes the product you want suppliers to certify, not merely a shop-floor nickname.
304 stainless steel sheet, ASTM A240/A240M, No. 4 finish, 1.50 mm nominal thickness, tolerance per the specified metric provisions, 1000 × 2000 mm, protective film requirements stated.
Examples: low-carbon steel, 304 stainless, 5052-H32 aluminum.
Include rolled condition, temper, finish and edge requirements.
Use mm or decimal inches; add gauge only in parentheses if helpful.
State whether inch-pound or metric provisions apply.
For galvanized steel, include ASTM A653/A653M and G/Z designation.
Specify certificates, inspection, packaging and traceability requirements.
Bottom line
Use the chart to translate—not to finish the specification
A standard metal thickness chart is valuable when it answers a narrow question: what nominal thickness is associated with this material-specific gauge reference? It becomes risky when the gauge number is treated as a complete drawing, order or acceptance rule.
For reliable fabrication:
- Select the correct material column and gauge system.
- Convert inches and millimeters with 25.4 mm per inch.
- Write the decimal thickness on the drawing and RFQ.
- Apply the correct product specification and tolerance system.
- Measure received material according to the inspection plan.
- Use actual thickness—not gauge shorthand—for cutting, bending and welding setup.
This workflow prevents the most important class of gauge error: using a perfectly accurate number from the wrong table.
Frequently asked questions
Standard metal thickness chart FAQ
What gauge is 1 mm sheet metal?
It depends on the material table. One millimeter is closest to 19-gauge standard steel at 1.062 mm, 20-gauge common stainless at 0.953 mm, and 18-gauge legacy B&S nonferrous at 1.024 mm. Specify 1.00 mm directly when that is the design requirement.
Is 16 gauge thicker than 18 gauge?
Within the same gauge system, yes. Standard steel is about 1.519 mm at 16 gauge and 1.214 mm at 18 gauge. Do not compare numbers across different material systems without the chart.
How thick is 16-gauge steel?
U.S. Standard Gauge lists 16-gauge sheet steel at approximately 0.0598 inch, which converts to about 1.519 mm.
How thick is 18-gauge stainless steel?
A common U.S. stainless supplier convention lists 18 gauge at 0.0500 inch or 1.270 mm. The order should still state decimal thickness and the applicable stainless product specification.
Are steel and aluminum gauges the same thickness?
No. A commonly reproduced legacy B&S nonferrous chart differs from the standard-steel chart. Modern aluminum sheet should be specified by alloy, temper and decimal thickness.
Does galvanized steel have the same thickness as steel?
The steel substrate has its own nominal thickness, while the zinc coating adds caliper thickness. The amount depends on the coating designation and distribution.
Does higher gauge mean thicker metal?
For the sheet-metal systems shown here, the relationship runs backward: a higher gauge number means a thinner nominal sheet. Other gauge systems may behave differently, so name the system.
Can I convert gauge to mm with one formula?
No single formula covers all materials because the charts use different conventions. Use the correct material-specific table, then convert inches to millimeters using 25.4.
Is nominal thickness the same as measured thickness?
No. Nominal thickness is the ordering target or reference value. Actual sheet may vary within the tolerance permitted by the governing product specification.
Should engineering drawings use gauge or millimeters?
Use decimal thickness in millimeters or inches as the primary dimension, together with material and tolerance requirements. Gauge can be included as secondary purchasing shorthand.
What tool should measure sheet-metal thickness?
An outside micrometer with suitable range, resolution, calibration and controlled measuring force is normally preferable for precision thickness checks. The inspection method must match the specification.
Does paint or protective film count in the thickness?
A direct caliper measurement includes layers between the anvils. The engineering or inspection requirement must state whether it applies to bare base metal, metallic coating or final finished caliper.
What is the difference between sheet and plate?
The dividing thickness is not universal across every material and industry. Use the definition in the applicable product specification rather than a generic gauge cutoff.
Can I use this chart to set laser-cutting or welding parameters?
Use it only to interpret a nominal gauge. Production parameters require confirmed material, coating, actual thickness, joint or cut geometry, machine configuration and validation.
Continue planning
Related fabrication resources
Source notes
Technical references
- 15 U.S.C. §206 — Standard gauge for sheet and plate iron and steel.
- NIST — SI Units: Length; one inch equals exactly 25.4 mm.
- ASTM Subcommittee A01.19 — A568/A568M steel sheet requirements.
- ASTM A480/A480M — Flat-rolled stainless general requirements.
- ASTM A653/A653M — Hot-dip zinc-coated and zinc-iron alloy-coated steel sheet.
- ASTM B209/B209M — Aluminum and aluminum-alloy sheet and plate.
- The Aluminum Association — ANSI H35.2M dimensional tolerances for aluminum mill products.
- GalvInfo Center — Galvanizing 2022 coating designation and nominal thickness tables.
Gauge conventions and product availability vary by supplier and region. Use the latest applicable product standard, drawing and purchase order for acceptance.
From thickness to process
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