Guide · Paint-thickness gauges
Can a paint gauge measure clear coat?
A magnetic or eddy-current paint gauge reads the whole paint stack, not the clear coat. What the published clear-coat figures are, and who says them.
Short answer
Not on its own. A magnetic or eddy-current paint gauge reads the whole stack from probe to metal (primer, color, clear coat, any repaint, filler and dirt) with no distinction between layers.[1] It cannot tell you how much clear coat is left. DeFelsko gives 35-50 µm as a typical clear coat thickness, but that is DeFelsko's rough figure, not a carmaker specification.[1]
What the number on the screen is
On a metal panel, an Fe/NFe gauge measures the full distance from the probe to the base metal. DeFelsko lists what that includes: primer, base color, clear coat, any repaint, filler and dirt.[1] The gauge adds them all up and shows one number.
So a reading of 120 µm is total coating, not clear coat. Two panels with the same total could have very different clear-coat layers.
Gauges that report layers
DeFelsko's PosiTector 200 B3, an ultrasonic gauge, can report total thickness and up to three individual layers. It is made for coatings over non-metals such as plastic bumpers and fiberglass, and it needs a couplant gel.[1] DeFelsko says its affordable ultrasonic models are intended only for non-metal substrates.[1]
We found no verified source for a layer-reading gauge on steel or aluminum car panels aimed at detailers, so on metal panels assume you get the total only.
The clear-coat figures you will see quoted
| Figure | Who says it | How to treat it |
|---|---|---|
| 35-50 µm (1.5-2.0 mils) typical clear coat | DeFelsko[1] | A rough figure from a gauge maker's article, not an OEM specification |
| Remove at most about 8 µm (0.3 mil) | DeFelsko, attributing it to "most auto manufacturers"[1] | DeFelsko's statement; it names no carmaker document |
We have no carmaker's own clear-coat thickness or removal limit in our sources. If your car's maker publishes refinishing guidance, follow it over any general figure.
Why a gauge cannot track polishing removal
DeFelsko's removal figure is about 8 µm. A gauge's own error band is not much smaller. UNI-T's stated accuracy for the UT343E, ±(2%H + 2 µm), works out to ±4 µm at 100 µm.[2] That is half of DeFelsko's 8 µm figure, before you add the difference from not hitting the exact same spot twice.
So a before-and-after reading can flag a large change, but it cannot show that you removed 2 µm rather than 6 µm. Use the gauge before polishing to find panels that read well below or above the rest of the car, and polish those conservatively. See paint gauge accuracy vs resolution.
Units
One mil is one thousandth of an inch, 25.4 µm; a micron is one thousandth of a millimeter.[1] DeFelsko gives its 35-50 µm figure as 1.5-2.0 mils.
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Questions
How thick is clear coat on a car?
DeFelsko gives 35-50 µm (1.5-2.0 mils) as typical. That is a gauge maker's rough figure, not a carmaker specification, and we have no OEM figure in our sources.[1]
How much clear coat can I safely polish off?
DeFelsko states that most auto manufacturers recommend removing at most about 8 µm (0.3 mil), but it names no carmaker document. Follow your own car maker's refinishing guidance if it publishes one.[1]
Can my gauge tell me the clear coat is getting thin?
No. A magnetic or eddy-current gauge shows the total from probe to metal, including primer, color, clear, any repaint, filler and dirt, with no distinction between layers.[1]