How to choose a coating thickness gauge
By Grant, Inspection Tool Specialists. Reviewed November 2026.
Two questions decide which coating thickness gauge you need: what metal is under the coating, and how thick the coating will be. A gauge for painted steel will not read on aluminium unless it has a non-ferrous probe, and a gauge with a 1,250 micron range will not measure a 3 mm anti-corrosion lining. Answer those two questions and most of the range falls away.
This guide covers dry film thickness (DFT) gauges for coatings on metal. If you need to check for pinholes, measure wet paint, or measure the thickness of the metal itself, those are different instruments, covered at the end.
What is under the coating?
Coating thickness gauges work by magnetic induction on steel and iron, and by eddy current on non-magnetic metals such as aluminium, brass, copper and stainless steel. Gauges are sold as one of three types:
| Gauge type | Measures coatings on | Typical use |
|---|---|---|
| Ferrous (F) | Steel and iron only | Structural steel, pipelines, vehicle bodies, galvanising |
| Non-ferrous (N) | Aluminium, copper, brass, austenitic stainless steel | Aluminium profiles, anodising, powder coating on aluminium |
| Combined (FN) | Both, with automatic substrate recognition on some models | Workshops and inspectors who meet both metals |
If you are not sure what you will be asked to measure, choose a combined FN gauge. The price difference is small and it saves a second instrument later.
None of these gauges measure coatings on concrete, wood, plastic or other non-metal surfaces. The answer is no: there must be a metal base for the probe to sense. Measuring coatings on non-metal surfaces needs a different method, so ask us and we will check with our suppliers.
How thick is the coating?
Most general-purpose gauges measure 0 to about 1,250 microns (1.25 mm). That covers paint, powder coating, galvanising, plating and most protective coatings applied in two or three coats. Typical values you will meet:
- Automotive paint: roughly 80 to 200 microns
- Powder coating: roughly 60 to 120 microns per coat
- Hot-dip galvanising: roughly 50 to 150 microns
- Two-coat epoxy on steel pipes: roughly 250 to 300 microns total
- Thick anti-corrosion linings, rubber and fibreglass: 1 to 10 mm and more
If your coating can exceed about 1 mm, choose a gauge with a thick-coating probe or a high-range model. A standard probe cannot measure above its range.
Built-in probe or separate probe?
- Built-in probe: one-hand operation, robust, best for flat and gently curved surfaces. The usual choice for inspection rounds and vehicle checks.
- Separate cabled probe: reaches inside pipes, into corners and onto small or curved parts, and you can watch the display while the probe is on the surface. Choose this for pipe interiors, fabricated assemblies and small components.
A V-groove on the probe face helps it sit squarely on pipes and round bar.
What accuracy and features do I need?
Accuracy is usually stated as a percentage of the reading plus a fixed amount. The MCT200, for example, is plus or minus 3 percent of the reading plus 1 micron. For a 100 micron coating that is about 4 microns either way, which is enough for a specification check. The features that matter more in practice are:
- Calibration foils and a zero plate supplied with the gauge, so you can check it against a known thickness on your own substrate before each job.
- Memory and statistics if you report averages, minimums and maximums over a batch of readings, which many coating specifications require.
- USB or Bluetooth output if readings must go into a report rather than be copied by hand.
- Continuous mode for scanning a large surface quickly to find thin spots.
Which gauge should I buy?
| Application | Suggested starting point |
|---|---|
| Painted or galvanised steel, routine checks, tight budget | M2110 digital gauge (ferrous) or M231 digital gauge (ferrous and non-ferrous) |
| Steel and aluminium, automatic substrate recognition, one-hand use | CM8806FN combined gauge or PCE-CT 26FN |
| Pipe interiors, small parts and awkward access | CM8811FN external-probe gauge or PCE-CT 27FN with V-groove sensor |
| Interchangeable probes for different jobs, data storage | MCT200 with F1, N1, F400 or N10 probe |
| Thick anti-corrosion linings up to 12 mm | AC-112H anti-corrosion coating gauge |
As a guide to our current range, prices run from about R4,800 for an entry-level digital gauge to about R14,000 for an external-probe or thick-coating model, including VAT. Prices change, so check the product pages.
When a coating thickness gauge is the wrong instrument
- Pinholes, holidays and thin spots in a protective coating are found with a high-voltage holiday detector for coatings above about 500 microns, or a wet-sponge holiday detector for thin coatings. A thickness gauge will not find them.
- Wet paint during application is checked with a wet film comb gauge, so you can adjust before the coating dries.
- Surface profile after blasting, which a coating specification often also calls for, is measured with a surface profile gauge.
- The thickness of the metal itself, for corrosion surveys, is measured with an ultrasonic thickness gauge, which measures the metal wall from one side.
Questions we will ask you
Tell us the base metal, the coating type and its specified thickness, whether you measure on flat surfaces or inside pipes and on small parts, and whether readings must be stored or reported. With that we can recommend a gauge and provide pricing.