How to convert microns to gauge thickness

Updated April 17, 2017

Whether you are purchasing trash bags for the garage, tin foil for the kitchen or sheet metal for your business, it is essential to buy the product with the right properties to get the job done. The properties of the product are determined by the material thickness. Manufacturers often report the thickness of their product in the form of a gauge number, which depends on the material type, rather than using the more common linear units. Converting material thickness to the industry equivalent gauge number ensures that the correct product is purchased.

Identify the material--e.g., plastic or metal--for which the film thickness conversion is required.

Classify the metal type as steel, galvanised steel, stainless steel, aluminium, copper or the appropriate alloy. Plastic need not be categorised, as gauge number scales are the same for all plastic types.

Take a minimum of three thickness measurements at various points on the material sheet, using the screw micrometer, and calculate the average thickness. Report the thickness in micron.

Multiply the plastic film thickness measured in micron by the conversion factor 3.937.

Round the result to three decimal places.

Report the result as a number followed by the word "gauge" to differentiate it from other commonly used units.

Convert the micron measurement to inches, as most sheet metal gauge tables only correlate thickness measurements given in inches with gauge numbers. Multiply the micron measurement by 3.937E-05 to obtain the equivalent measurement in inches.

Consult the Gauge and Weight Chart for Metals provided by the Engineering Toolbox or an equivalent gauge chart and isolate the sheet thickness column associated with the relevant metal--e.g., galvanised steel or aluminium. Gauge numbers for metals are based on the weight or density of the sheet metal, so the same gauge number refers to different thicknesses for different alloys or metal types.

Find the value in the table which is closest in magnitude to the thickness--in inches--requiring conversion, and read off the equivalent gauge thickness.


An increase in the thickness for metal films is indicated by a decrease in the gauge number. An increase in the thickness of plastic films is indicated by an increase in the gauge number. If the calculator does not have an exponent function, enter the value 3.937E-05 as 0.00003937.

Things You'll Need

  • Calculator
  • Screw micrometer
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About the Author

Pearl Lewis has authored scientific papers for journals such as "Physica Status Solidi," "Materials Science and Engineering" and "Thin Solid Films" since 1994. She also writes an education blog entitled Simple Science in Everyday Life. She holds a doctorate from University of Port Elizabeth.