Measuring the Thickness of Coatings on Metallic Material

Many of the material used in today’s products have some sort of coating, whether it’s galvanized coating or painting on the structural / marine / automobile materials. Coating thickness refers to the thicknesses of those coating. There are two different methods used to measure the coating thickness; a Magnetic Induction method and Metallography method.



Magnetic Induction Method: This technology measures non-magnetic coatings over ferrous substrates and magnetic coatings over non-magnetic substrates. When the probe is positioned on the sample, the linear distance between the probe tip that contacts the surface and the base substrate is measured.

Metallography Method: This test method consists of cutting out a portion of the test specimen mounting it, and preparing the mounted cross section by suitable techniques of grinding, polishing and etching. The thickness of the cross section is measured with an optical microscope.


Common case coating thickness specification are:


  • ASTM E3 – Standard Guide for Preparation of Metallographic Specimens
  • ASTM E407 – Standard Practice for Micro-etching Metals and Alloys.
  • ASTM B487 – Standard Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of Cross Section.
  • ASTM D7091 – Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous Metals


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