ASTM E376

Introducing ASTM E376 – Industrial Physics

ASTM E376 is the broad ASTM practice for measuring coating thickness using electromagnetic gauges – both magnetic-field-type and eddy-current-type instruments. It is the general, umbrella standard that sits above the more application-specific ASTM coating thickness methods, describing how these gauges work and how to use them for non-destructive measurement on a metal substrate.

Because it covers both measurement principles and applies to a wide range of substrate and coating combinations, ASTM E376 gives quality, R&D, and operations experts a single reference point for electromagnetic coating thickness measurement – whichever metal and coating they are working with.

What ASTM E376 Covers

ASTM E376 describes the use of magnetic-field and eddy-current thickness gauges for non-destructive measurement of a coating on a metal (electrically conducting) substrate. Key elements of the practice include:

• Both measurement principles: magnetic-field gauges (for coatings on ferrous metals) and eddy-current gauges (for coatings on non-ferrous metals)
• Ferrous or non-ferrous substrates, and coatings that may be conductive or insulating – the broadest scope of the ASTM coating thickness standards
• How the two gauge types operate, their limitations, calibration, and the factors that affect accuracy
• A general framework under which the more specific ASTM methods are applied

ASTM E376 is the general practice, and it points to more specific methods for particular applications – including Practice D7091 and Test Methods B244 (anodic coatings on aluminium), B499 (magnetic method on ferrous metals), and B530. It aligns with the requirements of the ISO magnetic method, ISO 2178.

The current version is ASTM E376-19, published under ASTM Committee E07 on Nondestructive Testing. It’s worth confirming the current revision at the time of publishing, as ASTM reviews its standards on a regular five-year cycle.

Why Coating Thickness Matters

Coating thickness is one of the clearest indicators of how a coating will perform. Too little and the part may not be properly protected against corrosion or wear. Too much and material is wasted, and the coating may crack or lose adhesion. Being able to measure it accurately – on any metal, with the right technique – and prove it, is central to quality control across coating and finishing operations.

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

• Confirm coatings meet the specified thickness for corrosion protection and durability
• Measure confidently across ferrous and non-ferrous parts using one consistent electromagnetic practice
• Meet customer, contract, and specification requirements with measurable evidence
• Control coating usage and cost by avoiding both under- and over-application
• Support product development and finishing work with repeatable data

Because coating thickness is easy to get wrong by eye but simple to prove with a correctly calibrated gauge, a standardised practice like ASTM E376 protects the integrity of both the coating and the customer relationship – across protective coatings, automotive, aerospace, marine, industrial, and general metal finishing.

How ASTM E376 Testing Works

ASTM E376 covers two gauge principles. Magnetic-field gauges work on coatings over ferrous (magnetic) substrates: they sense either the magnetic attraction between a magnet and the steel, or the change in a magnetic flux path through the coating and substrate – the coating holds the probe away from the steel, and that gap is displayed as thickness. Eddy-current gauges work on coatings over non-ferrous (conductive) substrates: a high-frequency coil induces eddy currents in the metal, and the gauge measures the change in the coil’s impedance caused by the coating gap.

In both cases the measurement is non-destructive – nothing is cut or removed – and accuracy depends on calibrating the gauge against known reference standards and using it under suitable conditions. Selecting the right principle for the substrate, calibrating correctly, and measuring this way is what makes the result repeatable and defensible.

ASTM E376 Testing Equipment

Industrial Physics offers a coating thickness gauge from TQC Sheen that supports ASTM E376 electromagnetic coating thickness measurement.

TQC Sheen PosiTector 6000 Coating Thickness Gauge

The TQC Sheen PosiTector 6000 fits ASTM E376 especially well, because the practice covers both electromagnetic principles and the gauge uses both. It applies the magnetic-field method on ferrous substrates like steel and cast iron and the eddy-current method on non-ferrous metals like aluminium and copper, automatically recognising the substrate and measuring accordingly – a rugged, fully electronic instrument for both principles in one device.

Typical features include:

• Magnetic-field and eddy-current measurement in one gauge, with automatic substrate recognition
• 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 additional compliance modes
• Rugged, weatherproof design with built-in temperature compensation for reliable readings in the field

The PosiTector 6000 conforms to a wide range of national and international standards, including ASTM E376, ASTM D7091, ASTM B244, and ASTM B499, alongside ISO 2178, ISO 2360, ISO 2808, and ISO 19840. If you’re not sure which model or probe best fits your substrates and coatings, our experts can help guide you to the right choice.

Your Global Test and Measurement Partner for ASTM E376

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 ASTM E376. Whether you’re measuring a coating on steel, on aluminium, or across a mixed range of parts, we can help you achieve accurate, repeatable, and reliable coating thickness results.

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