ISO 2178

Introducing ISO 2178 – Industrial Physics

ISO 2178 is the international standard that sets out the magnetic method for measuring the thickness of non-magnetic coatings on magnetic (ferrous) substrates. In plain terms, it’s how you accurately measure the thickness of a coating – such as paint, powder coating, enamel, plating, or galvanizing – on steel or iron, without damaging the coating or the part.

It gives quality, R&D, and operations experts a fast, non-destructive, and repeatable way to confirm that a coating has been applied to the specified thickness – which is one of the clearest indicators of how well that coating will protect the part underneath.

What ISO 2178 Covers

ISO 2178 specifies how to use a magnetic-type coating thickness gauge for non-destructive measurement of coating thickness. Key elements of the method include:

• Measurement of non-magnetic (non-magnetizable) coatings on magnetic base metals, such as steel and iron
• Coatings covered include paints and varnishes, electroplated coatings, enamel coatings, plastic and powder coatings, and claddings
• A tactile, non-destructive measurement made by placing the probe (or a gauge with an integrated probe) directly on the coating
• Calibration and verification of the gauge against reference standards to keep readings accurate
• Guidance on the factors that affect a reading, such as substrate thickness, curvature, edge effects, and surface roughness

The current version is ISO 2178:2016 (the third edition, published March 2016), which cancelled and replaced the 1982 edition. It was reviewed and confirmed in 2021, so it remains current. The committee responsible is ISO/TC 107, Metallic and other inorganic coatings. It’s worth confirming the current revision at the time of publishing, as ISO reviews its standards on a regular cycle.

Why Coating Thickness Matters

Coating thickness, often called dry film thickness (DFT), is one of the most important checks in any coating or finishing operation. Too little coating and the part may not be properly protected against corrosion or wear. Too much and you waste expensive material, risk cracking or poor adhesion, and add unnecessary cost. Getting it right – and being able to prove it – protects both the product and the bottom line.

A reliable coating thickness measurement helps quality, R&D, and operations experts to:

• Confirm coatings meet the specified thickness for corrosion protection and durability
• Control paint and coating usage, reducing waste from over-application
• Meet customer, contract, and warranty requirements, backed by measurable evidence
• Catch application problems early, before parts leave the line
• Support consistent quality across shifts, operators, and sites

Because coating thickness is easy to get wrong by eye but simple to prove with a gauge, a standardised method like ISO 2178 protects the integrity of both the coating and the customer relationship – especially for protective coatings on steel structures, and across automotive, marine, industrial, and general metal finishing.

How ISO 2178 Testing Works

The magnetic method relies on a simple principle: a probe generates a magnetic field, and the strength of that field – or the magnetic flux between the probe and the steel or iron underneath – depends on how far the probe tip sits from the substrate. That distance is the coating.

When the probe is placed on a coated part, the non-magnetic coating holds the probe tip a small distance away from the ferrous metal. The gauge measures the change in the magnetic field caused by that gap and converts it directly into a coating thickness reading, shown on the display in a matter of seconds. Because nothing is cut or removed, the part stays fully usable.

To keep results trustworthy, the gauge is calibrated and verified against known reference standards, and readings are taken carefully with attention to substrate shape, edges, and surface condition. This controlled, repeatable approach is what gives quality control teams results they can act on with confidence.

ISO 2178 Testing Equipment

Industrial Physics offers a coating thickness gauge from TQC Sheen that supports ISO 2178 magnetic-method coating thickness testing.

TQC Sheen PosiTector 6000 Coating Thickness Gauge

The TQC Sheen PosiTector 6000 is a rugged, fully electronic coating thickness gauge that measures coatings on both ferrous and non-ferrous metals. For ISO 2178 testing, it uses the magnetic method on ferrous substrates like steel and cast iron, and it automatically recognises the substrate to take the right measurement – so the same gauge also handles non-ferrous substrates using the eddy-current method (ISO 2360).

Typical features include:

• Magnetic and eddy-current measurement, with automatic substrate recognition for ferrous and non-ferrous metals
• Suitable for a wide range of coatings, including paint, powder coatings, galvanizing, anodizing, and plating
• A wide range of interchangeable Ferrous, Non-Ferrous, and Combination probes
• Standard and Advanced models, with the Advanced model adding a colour touchscreen, real-time graphing, and compliance modes for SSPC-PA 2, ISO 19840, and PSPC 90/10
• Rugged, weatherproof design with built-in temperature compensation for reliable readings on the shop floor

The PosiTector 6000 conforms to a wide range of national and international standards, including ISO 2178, ISO 2360, and ISO 2808, ISO 19840, and ASTM methods such as B499, D7091, and E376. If you’re not sure which probe or model best fits your substrates and coatings, our experts can help guide you to the right choice.

Your Global Test and Measurement Partner for ISO 2178

Industrial Physics supports quality, R&D, and operations experts around the world with the paint and coating test and measurement expertise needed to work confidently with standards like ISO 2178. Whether you’re checking corrosion protection on a steel structure, controlling paint usage on a production line, or developing a new coating system, we can help you achieve accurate, repeatable, and reliable coating thickness results.

Get in touch to talk through your coating thickness measurement requirements.