Paint-check guidelines
How to check a car body with a thickness gauge
Checking a body with a thickness gauge is an important step when buying a car. Understanding how measurements work helps you avoid a vehicle with hidden damage.
About thickness charts
Don’t trust charts blindly
Even cars from the same plant can have slightly different paint layers from batch to batch. The exact thickness matters less than consistency — the coating should be even across the whole body. Large variation between panels, or small repainted “islands”, is a sure sign of repair.
See figures by make and modelThe roof as a reference
Start with the roof
The roof is usually the best comparison point: a car rarely flips over, so its paint is almost always original. Measure the roof first and use that reading as your baseline for the other panels.
Walk-around order
Cover the whole body, not a few spots
Checking a couple of places proves nothing: repairs are often local, and hitting one by chance is luck. Walk around the car and take readings on every exterior panel. That is about fifteen points and roughly ten minutes.
- 01
Roof
The first panel and your baseline — every check starts here.
- 02
Hood and boot lid
Horizontal panels take stones and hail first, and are repainted more often than the rest.
- 03
Doors and wings
Go around and compare in pairs: left with right, front with rear.
- 04
Pillars and sills
They get looked at least, yet a panel replaced after a serious hit shows up exactly here.
Measuring technique
How to hold the gauge
The reading depends on how the gauge is held. It measures a spot around the probe rather than a point, so near a panel edge, on a crease or at a rim you get an edge effect and the reading drops.
- Hold the probe perpendicular to the surface, firmly and without skew.
- Do not move the gauge until it beeps: shifting mid-measurement ruins the result.
- Stay at least a centimetre away from panel edges, creases and rims.
- The surface must be clean and dry — dust between probe and paint adds 5–10 micrometres.
- Take two or three readings in one area: a single number means nothing yet.
What thickness is normal
A baseline of 80–180 µm
On most vehicles the factory paint layer is around 80–180 µm, with a tolerance of ±10–30 µm. These values indicate original paint with no repainting. A reading above 200 µm on most models suggests the panel has been repainted.
Average factory paint by region
| Region | Thickness |
|---|---|
| European | 90–180 µm |
| Japanese | 80–160 µm |
| Korean | 70–140 µm |
| Russian | 60–150 µm |
| Chinese | 90–200 µm |
| American | 90–190 µm |
Acceptable variation
What counts as normal
- Variation on a single panel of ±10–30 µm is normal.
- Paint on vertical panels and the roof is usually thinner.
- Three-layer paints (pearl, metallic) are 20–30 µm thicker.
- Protective films add about 100–150 µm to gauge readings.
- Inner body panels usually measure 40–80 µm.
The main rule
Compare symmetrical panels
Compare not the numbers but symmetrical panels — for example, the left and right fenders. If the readings are similar, both parts are likely original. A significant difference means one of them was repaired or replaced.
False readings
What will mislead you
Paint protection film
Polyurethane film adds 100–150 micrometres and looks like a respray. If the whole body reads exactly plus one hundred, look for film, not repair.
Plastic panels
Bumpers — and on many cars the wings too — are plastic. A magnetic probe does not work on them at all; that is not a fault.
Aluminium panels
Aluminium hoods and doors are measured by the eddy-current method. A gauge with automatic metal recognition switches by itself; a single-range one does not.
Frost and moisture
Measure a dry body: a film of water or ice sits on top of the paint and goes straight into the reading.
Frequently asked
Frequently asked
How many points should you measure when checking a body?
Work across the body on a grid of roughly 15 centimetres, and go denser on the panels that suffer most — wings and doors. If you find a thicker spot, do not move on: take several readings around it and find the point of maximum thickness. That is the centre of the damage, and readings in a circle around it show its extent. Go over pillars in small steps of one or two centimetres: that is how welds are found.
What if the roof has been resprayed too?
Then compare symmetrical panels with each other: left wing against right, left door against right. A second reference is the inner surfaces and door apertures — factory paint there is almost never touched.
Does the gauge read on a bumper?
No. The gauge measures the layer between metal and probe tip, and a bumper is plastic: there is no metal under the coating, so there is nothing to measure. This is not a fault — on plastic a gauge of this type shows nothing at all.
Can you measure a car in the rain?
Water droplets on the body do not affect the readings. But the gauge has no water protection, so measure in a way that keeps water out of the housing.
Does dust on the car affect measurements?
Yes: dust or dirt between the probe tip and the paint is counted as part of the coating and inflates the reading. The effect is small, though — the CARSYS probe is spherical and touches the surface over less than a square millimetre. On a dusty car it is enough to wipe the measuring point or pick clean areas.
How should you hold the gauge while measuring?
Hold it closer to the probe — that way the gauge is easier to press flat and without skew. A common mistake is holding it by the tail end: the body is then hard to press against the surface and wobbles from side to side.
The gauge shows no galvanising, although the car is said to be galvanised. Why?
Manufacturers change their processes without announcements, and different plants build the same model slightly differently. Often it is not the whole body that is galvanised but only the panels that suffer most from corrosion: sills, wings, doors. More often still you meet so-called cold galvanising, or cataphoresis — which is not classic galvanising at all. It is essentially a primer filled with zinc: it is not electrically conductive, so to a gauge it is no different from ordinary coating. That property has a useful side — you cannot apply zinc-rich primer before painting and fool the gauge.
Why does the gauge stop showing galvanising above 1500 µm?
At that thickness the panel-replacement clue is no longer needed: 1500 micrometres and above is already an excessively thick layer, so the damage has been found without any zinc indication.
What to do with a finding
A deviation is not a reason to walk away
A gauge check gives you facts, not a verdict. A resprayed wing and filler in a sill are different stories, and they call for different decisions.
One panel out of fifteen
A repainted bumper or wing is ordinary on a used car. On its own that is city life, not a hidden crash.
Look at the area
A local 300 µm spot is probably a filled scratch. An even layer across the whole panel means it was resprayed entirely.
Count adjacent panels
Two neighbouring panels with the same deviation point to an impact that landed on the joint. A single one is more likely cosmetic.
Structural parts are different
Filler on a pillar, sill or chassis rail matters more than on a door: there it can hide geometry work.
The sensible outcome of a check is not “buy or walk” but understanding what actually happened to the car. After that it is either a bargaining point or a reason to look at the next one.
Types of body repair
What the gauge reveals
01
Minor repair
A repaint (for example, after a scratch) adds roughly 50–100 µm to the total thickness.
02
Dent repair
If a panel was repaired with filler, the readings in those areas will be 300 µm or more.
03
Serious damage
If you find filler measuring 1000 µm (1 mm) or more, it’s best to walk away — that area may eventually peel or separate.
Thickness values are approximate and vary with production year, factory and market region.
Knowledge base
Read next
Material that carries the topic on: how to check a body, what the gauge does and which one to choose.
Check a body with an accurate device
The method only works with a reliable gauge. Choose a CARSYS device that fits your work.