Gauge number is a convenient shorthand for sheet thickness, but the conversion depends on material and chart. These selected values come from one fabricator’s stainless-steel chart. They are not a universal conversion for carbon steel, galvanized sheet, aluminum or copper. When a drawing or purchase order names a thickness in inches or millimetres, use that specified dimension and its tolerance instead of relying on gauge alone.

Sheet Metal Gauge Conversion and Thickness

Read the stainless-steel chart

In the cited chart, lower gauge numbers correspond to thicker stainless sheet. For example, the 10-gauge entry is 0.14062 inch (3.5710 mm), while 18 gauge is 0.05000 inch (1.2700 mm). The same number should not be assumed to represent the same thickness in another material system. Gauge conventions developed separately and the source values must stay attached to their stainless-steel scope.

The table includes selected points from gauges 10 through 24. It omits other gauges, grades, tempers and product conditions. The chart’s millimetre values are its rounded equivalents; they are not a second independent measurement. A calculator converting from the inch figure may show a small difference because of the rounding basis.

Do not specify by gauge alone

For procurement, state material grade, product form, nominal thickness and applicable specification. Gauge may be included as a familiar reference, but it should not replace the controlled dimension where thickness affects strength, fit, mass, forming allowance or a welded joint. If a drawing uses a gauge term, confirm that buyer and supplier reference the same material-specific chart.

Nominal chart thickness is not the permitted range for delivered sheet. Tolerance depends on material specification, width, product form and sometimes ordered thickness range. The supplier chart does not establish a tolerance or certify a particular sheet. Use the product specification and inspection records for acceptance.

Compare materials carefully

Stainless, carbon steel, galvanized steel and aluminum can have different gauge-to-thickness relationships. A galvanized product also has a metallic coating that may be included in measured thickness under the relevant product standard. Do not combine a stainless entry with a steel gauge chart or infer coating thickness from a nominal gauge number.

If comparing designs made from different materials, compare actual specified thickness and grade rather than gauge labels. Mechanical properties, corrosion resistance and forming behavior are not encoded in the gauge number. Similar nominal thickness also does not guarantee equal stiffness or strength.

Unit conversion and measurement

One inch equals exactly 25.4 millimetres. Values can be converted from inches, but the table preserves millimetre figures as reported by the source so readers can reproduce its chart. If a calculation is sensitive to the final decimal place, convert from the governing dimension using unrounded inputs and retain the specified tolerance separately.

For incoming inspection, use a calibrated thickness instrument and the method required by the material specification. Account for surface texture, protective film and coating where relevant. Gauge label cannot replace measurement, certificate review or a dimensional acceptance plan.

Example conversion

The RMFG chart lists 16 gauge stainless steel as 0.06250 inch and 1.5870 mm. Multiplying 0.06250 by 25.4 gives 1.5875 mm, which explains why a value recomputed from the inch column can differ in the last decimal from the chart’s rounded millimetre entry. Preserve the source basis when reproducing the table, and use the specified nominal dimension rather than either rounded display value when a drawing controls the part.

The 12-gauge entry is shown as 0.10937 inch and 2.7780 mm. This is useful for a quick comparison within the same chart, but it does not mean every stainless grade or supplier delivers sheet at exactly that measured thickness. Surface condition, coating, width and applicable tolerance must be handled under the ordered product specification.

Source and scope

The eight entries are selected from RMFG’s stainless-steel gauge thickness chart. The chart is a fabricator reference, not a standards publication. Other metals use different charts, and exact ordering and acceptance requirements should follow the drawing, supplier agreement and applicable material specification.