ISO 19840-2012 "Paints and varnish - Criteria for measurement and acceptance of dry-film thickness on rough surfaces" is the international standard for coating dry-film thickness on rough surfaces. This standard was developed by ISO/TC 35/SC 14 as a supplement to the ISO 12944 series and applies to protective coatings systems for steel structures. The standard specifies a uniform method for instrumental measurement of dry-film thickness using the principle of permanent and induction magnets and describes the application of eddy current measurement equipment. For rough surfaces, the measurement complexity is high, especially when the coating is sand blasting or abrasion prepative on steel substrates. This standard provides detailed guidance on instrument calibrating, inspection area definitions, sampling plans and acceptance criteria to ensure Reliability and conformity of measurement results. ISO 19840-2012 applies to coatings of nominal dry-film thickness greater than or equal to 40 μm and provides important technical support and operational guidance for the Coatings industry and steel structure protection.