Paint Depth Gauge

Paint depth gauges can be used to measure the thickness of car paint. There are various mechanisms by which they work, mechanical gauges use magnets but can only be used over ferrous metals. Ultrasonic and Eddy Current can be used on other materials. Advanced models can not only tell the total thickness of the paint coatings, but also produce a graph from which it is possible to distinguish clear-coat from base coat.

These tools became popular in the boutique detailing industry and among enthusiasts around 20 years ago for measuring paint thickness, as a more scientific approach to polishing cars.

As polishing removes material from the paint surface, especially when wet-sanding is involved, it can be essential to know how much paint is left on the car. This is certainly the case for cars which are repeatedly polished, as in the case of show cars.

Controversy

Since they became 'popular' in certain circles within the industry, there has been controversy about paint depth gauges. Opinions vary as to their usefulness, with some saying they are a useful if not essential tool, to others saying they are just a gimmick to make detailers look more professional.

Early in their history within the detailing industry, they were the cause of much drama between a celebrity detailer and Ferrari over the actual thickness of their paint. With many detailers, professional and hobbyists publishing their work on YouTube, there have been numerous examples shown of paint depth gauges giving false or misleading readings.

We take a view, similar to that expressed in the video above from Canadian Gearhead. Experience, the evidence of your own eyes and common sense is generally better than working to the numbers.

What it means

A paint depth gauge is a handheld electronic tool that tells you how thick the paint is on a panel. You place the probe flat on the surface and it gives a reading, usually in microns (thousandths of a millimetre). On metal panels it typically uses magnetic or eddy current methods to measure the total coating stack – primer, basecoat and clearcoat together. More advanced gauges can also read on aluminium and some plastics with the right probe.

Why it matters

• Sets safe limits for polishing: Knowing paint depth helps detailers decide how aggressive they can be with machine polishing or wet sanding without risking burn-through.
• Helps spot repaints and repairs: Refinished panels often have noticeably higher or more uneven readings than original factory paint, which is useful when inspecting used cars or lease returns.
• Shows thin and risky areas: Very low readings on bonnets, roofs or high points can indicate previous heavy polishing or factory thinness, so technicians know to tread carefully or refuse certain correction work.
• Supports clear explanations to customers: Gauge readings provide an objective way to explain why some defects can be safely removed while others should be left alone or need repair and repaint.

Where you’ll see it

You will see paint depth gauges mentioned on professional detailing menus, inspection reports and bodyshop appraisals. Typical phrases include readings taken with paint depth gauge, low readings on edges or high paint depth indicates previous respray. They are commonly used during paint correction consultations, pre-purchase inspections and when assessing classic or prestige vehicles.

Context

A paint depth gauge is a key part of modern, risk-managed polishing and refinishing. Factory clear over base systems only give a limited amount of clearcoat to work with, and every correction removes a little more. By mapping paint readings across a car, technicians can build a picture of where the paint is original, where it has been repainted, and where it is thin or uneven. This information feeds into decisions about machine choice, pad and compound selection, whether to attempt flat and polish, and when to recommend repair and repaint instead of further correction.

Common mistakes

• Assuming that a high reading always means “safe” paint to attack heavily, without considering that a thick, unknown repaint can still be fragile or poorly adhered.
• Relying on a few random readings instead of building a proper map across each panel, missing localised thin spots on edges and high points.
• Using a gauge designed only for steel on aluminium panels or plastics and trusting obviously incorrect readings.
• Quoting micron numbers to customers without explaining that only part of the total thickness is clearcoat and that there are still limits to what correction can safely achieve.

Written by Danny Argent. Last updated 21/11/2025 15:38