Tool · Paint-thickness gauges
Paint gauge surface finder
Pick a body surface to see which paint gauge method reads it (magnetic, eddy current or ultrasonic), what the reading includes and what to check first.
Short answer
Choose a surface in the finder on this page to see which gauge method can read it, what the reading includes and what to check before you measure or polish. The short version: steel reads with a magnetic (Fe) gauge, aluminum with an eddy-current (NFe) gauge, and plastic or fiberglass only with an ultrasonic gauge.[1]
Which method reads which panel
| Surface | Gauge method | What to expect |
|---|---|---|
| Steel panels | Magnetic, Fe mode | Reads the full paint stack to the steel[2] |
| Aluminum panels | Eddy current, NFe mode | Reads the full paint stack to the aluminum[1] |
| Plastic bumpers | Ultrasonic, with couplant | No reading on an Fe/NFe gauge is expected[2] |
| Fiberglass panels | Ultrasonic, with couplant | Layer reporting depends on the model[2] |
UNI-T explains that FE means magnetic substrates such as iron and steel, NFE means non-magnetic metals such as aluminum and copper, and that Fe/NFe readings need a metal object with a non-conductive coating.[3] DeFelsko's PosiTector 200 ultrasonic gauge measures coatings over plastic bumpers and fiberglass, needs a couplant gel, and in its B3 model can report total thickness and up to three individual layers.[2]
One car can mix all of these. DeFelsko notes that recent vehicles can combine steel doors and fenders, aluminum hoods and roofs, and plastic bumpers and mirrors.[1] That is why a combination Fe/NFe gauge suits most used-car checks.
Layers and repairs
The finder also covers what sits on the panel:
- Clear coat: an Fe/NFe gauge cannot isolate it, because it reads the whole stack.[2]
- Factory paint and refinished panels: published ranges and comparison methods, never a pass or fail number.
- Body filler repairs and tin-filled repairs: AUTO BILD notes that tin-filled repairs on steel only show up on a gauge with NFe capability.[4]
The two family pages, metal panels and non-metal panels, group the substrates.
What each surface page shows
- Material and gauge method: which principle reads it and which mode to select.
- What the reading includes: for metal panels, everything from probe to metal, including primer, color, clear coat, repaint, filler and dirt.[2]
- Published thickness: figures from named sources, side by side, where they exist.
- Inspection tip and polishing note: what to check before measuring or polishing that surface.
Where the data comes from
Every confirmed field carries its source. Gauge makers come first: DeFelsko's automotive inspection and detailing articles and UNI-T's gauge FAQ. Independent sources, such as AUTO BILD's 2021 paint-gauge test of German-market gauges, are named as such and dated. Paint-maker figures, such as PPG's Australia and New Zealand refinish guidance, are labeled with their region. When no source we checked confirms a value, the field says "Not confirmed".
A surface page tells you what a gauge can read, not what a reading means for a car's history: a gauge shows thickness, not the cause. The used-car paint inspection overview explains how to compare readings, and the paint thickness gauges overview covers choosing a gauge.
Choose your surface to see the key facts. Each one links to its source on the full page.
Questions
Which gauge reads an aluminum hood?
An eddy-current gauge, or a combination gauge in NFe mode. DeFelsko says paint over aluminum and other non-ferrous metals is measured with eddy-current gauges.[1]
Why does the finder list plastic bumpers if my gauge cannot read them?
So you know a blank reading there is expected. DeFelsko says plastic and fiberglass need an ultrasonic gauge, such as its PosiTector 200, used with a couplant gel.[1][2]
How do I know what a panel is made of?
Check the car's documentation or a body shop. DeFelsko notes that recent vehicles can combine steel doors and fenders, aluminum hoods and roofs, and plastic bumpers and mirrors, so do not assume one material for the whole car.[1]
Why do some fields say 'Not confirmed'?
We show a value only when a maker, certifier or named independent source states it. When none does, the field says so instead of guessing.