Buying task · Used-car paint inspection
Used-car paint inspection with a gauge
How to check a used car's paint with a gauge: find the panel material, compare panels and mirrored spots, and know why no single number proves a repaint.
We may earn a commission if you buy through links on this page, at no extra cost to you. Unless a page says otherwise, our picks come from published specifications and listing research, not hands-on testing. As an Amazon Associate I earn from qualifying purchases. How we make money · How we research
Short answer
Find out what each panel is made of, measure every panel in the same places, and compare: adjacent panels with each other and each spot with the same spot on the other side.[1][2] Use a combination Fe/NFe gauge so steel and aluminum both read. A gauge shows thickness, not the cause, so an odd reading is a question to ask, not proof of a repaint.
What a gauge can tell you on a used car
A magnetic or eddy-current gauge reports the total distance from the probe to the metal: primer, color, clear coat, any repaint, filler and dirt together, with no split between layers.[3] That makes it useful for spotting where a car's coating changes, and useless for proving why it changed.
Know the panel material first. DeFelsko notes that recent vehicles can combine steel doors and fenders, aluminum hoods and roofs, and plastic bumpers and mirrors.[1] Steel reads in Fe mode, aluminum in NFe mode, and plastic or fiberglass needs an ultrasonic gauge instead.[1] A blank reading on a plastic bumper is expected, not a fault.
There is no single "normal" number
Published figures for factory paint differ, so treat each as one source's guidance, not a pass or fail line:
| Source | What it says |
|---|---|
| DeFelsko | Factory paint typically 100-180 µm, but no absolute "right" thickness: some roofs about 75 µm, some SUV rocker panels about 430 µm[3] |
| PPG Refinish (Australia and New Zealand) | Approximate OEM finish 90-120 µm; refinish films of 300 µm or more should be removed or sanded back[4] |
| AUTO BILD (2021, German market) | Factory finishes usually 80-150 µm and manual repaints typically above 200 µm, given as rough guidance only, with a warning that factories sometimes repaint[2] |
DeFelsko also notes that some vehicles are repainted at the factory.[3] The normal paint thickness guide puts these ranges side by side.
The key decisions
Compare panels, not numbers. DeFelsko advises looking for consistent thickness around the vehicle and measuring near seams about one inch from the edges, and it says a significant difference between adjacent panels strongly indicates repainting.[1] We would put it more cautiously: a difference is a reason to look closer.
Compare mirrored spots. AUTO BILD compares the same spot on both sides: a much higher reading on one side than on the other suggests a repair with repaint.[2] It also says interpreting readings takes experience with vehicle generations and paint systems.
Use both modes on steel cars too. AUTO BILD notes that tin-filled repairs on a steel body can only be found with a gauge that also has NFe capability.[2]
Expect filler to behave oddly. In one DeFelsko case study, readings around a vehicle were 105-115 µm, but one lower front panel read 270 µm and then 930 µm, which turned out to be plastic body filler over a rust repair.[1] That is one car, not a threshold for others.
Every page in this topic
Guides
- How to check a used car's paint with a gauge
- Normal car paint thickness: why there is no single number
- How to spot a repainted panel with a paint gauge
- Can a paint gauge detect body filler?
- Paint gauge readings that mislead: edges, curves, filler and drift
Surface pages
- Factory paint: the published ranges
- Refinished panels: comparison methods
- Body filler repairs
- Tin-filled repairs
Gauge types, accuracy and calibration are covered in the paint thickness gauges overview, and the surface finder shows which gauge reads each panel.
How to choose a gauge for inspection
- Fe/NFe in one tool, so steel and aluminum panels both read and tin-filled repairs on steel can show up.
- A range well above the readings you expect, so filler does not push the gauge off scale.
- A way to check it before use, such as zero plates or a reference film.
UNI-T specifies the UT343E for ferrous and non-ferrous substrates with a 0-2000 µm range,[5] and its where-to-buy page links no AliExpress or Amazon store.[6]
A paint reading is an observation, not a verdict on the car's history. If a car matters to you, have a qualified body shop or inspector look at any panel that reads differently.
Next
Everything in this topic
Guides
- Can a paint gauge detect body filler?Helps you recognize a likely filled area on a used car and know what the gauge can and cannot prove.
- How to check a used car's paint with a gaugeGives you a repeatable routine for a pre-purchase paint check and a sober way to read the results.
- How to spot a repainted panelShows you how to find panels worth questioning on a used car without over-reading a single number.
- Normal car paint thicknessStops you judging a car against a single 'normal' paint number that no source supports.
- Paint gauge readings that misleadHelps you tell a real difference between panels from a measuring error before you act on it.
Common questions
What does body filler read like on a paint gauge?
As much thicker coating than the paint around it. In one DeFelsko case study a panel read 270 µm and then 930 µm against 105-115 µm elsewhere, and it turned out to be plastic filler over a rust repair. More in Can a paint gauge detect body filler?
Why does my gauge show no reading on one spot of a metal panel?
DeFelsko says no reading may mean the thickness exceeds the gauge's limit, which could mean filler. Check the mode, the edge distance and that the part is metal first. More in Can a paint gauge detect body filler?
Can filler fool a paint gauge?
DeFelsko warns that some magnetic instruments can be fooled when steel particles are added to body filler, even on steel. More in Can a paint gauge detect body filler?
Can a steel-only gauge find tin filler?
No, according to AUTO BILD: tin-filled repairs on a steel body can only be found with a gauge that also has NFe (eddy-current) capability. More in Can a paint gauge detect body filler?
Where should I measure on each panel?
Several points per panel on clean, flat areas, staying about one inch from edges and seams as DeFelsko advises, and the same spots on both sides of the car. More in How to check a used car's paint with a gauge
Does a thicker panel mean the car was in an accident?
Not by itself. A gauge shows thickness, not the cause, and AUTO BILD notes factories sometimes repaint. Treat a difference as a reason to look closer and ask. More in How to check a used car's paint with a gauge
Why do I get no reading on part of the car?
On a bumper or mirror the part may be plastic, which Fe/NFe gauges cannot read. On metal, DeFelsko says no reading may mean the coating is beyond the gauge's limit, which could mean filler. More in How to check a used car's paint with a gauge
Do I need a gauge with NFe mode for a steel car?
It helps. AUTO BILD notes tin-filled repairs on a steel body can only be found with a gauge that also has NFe capability, and many cars mix steel and aluminum panels. More in How to check a used car's paint with a gauge
Questions
Does a reading above 200 µm mean the car was repainted?
Not on its own. Published ranges differ: DeFelsko calls 100-180 µm typical factory paint, PPG's Australia and New Zealand refinish guidance gives about 90-120 µm, and AUTO BILD calls its own figures rough guidance and warns that factories sometimes repaint.[3][4][2]
Why does my gauge show nothing on the bumper?
Bumpers are often plastic, and magnetic or eddy-current gauges cannot read paint over plastic. DeFelsko says plastic and fiberglass need an ultrasonic gauge.[1]
What is the most useful comparison on a used car?
Compare like with like. DeFelsko looks for consistent thickness around the car and differences between adjacent panels, and AUTO BILD compares the same spot on both sides of the car.[1][2]
Do I need an Fe/NFe gauge if the car is all steel?
It helps. AUTO BILD notes that tin-filled repairs on a steel body can only be found with a gauge that also has NFe (eddy-current) capability.[2]
Can a gauge tell me whether the car was in an accident?
No. A gauge shows how thick the coating is, not why. Treat an unusual reading as a reason to ask questions or book a professional inspection.