How to USE a Coating Thickness Gauge

coating thickness gauges

What is the first idea to pop into your head whenever such an item as a coat thickness gauge (CTG) is mentioned? Automotive business, car paint, auto body repair do to come to mind, don’t they? And rightly so, as CTGs do play a big part in evaluating the thickness of car paint, helping determine whether factory paint job has been tampered with, how much paint is left to work with, etc … But there is so much more to CTGs that you need to know if you are to get your money’s worth out of a potential purchase. We’ve put together a concise CTG 101 to bring you into the loop!

What is a CTG and What is it Good For?

CTG, popularly known as a paint meter, is a device used to measure dry film thickness (DFT). Simply put, DFT is the thickness of the coating as measured above the substrate. Why even bother when purchasing a brand-new product, you might wonder? A legitimate query and the answer is very prosaic – nothing serves as a better benchmark in appraising coating’s projected lifespan, overall product quality, future performance, and general appearance than a pin-point accurate coating thickness measurement (CTM).

What are CTMs prime Targets?

CTMs can be done on various magnetic substrates such as iron, steel, mild steel as well as nonmagnetic ones, including stainless steel, aluminum, copper, tin, gold – (the difference between the two is the former has iron content and the latter does not). CTM’s are primarily used to appraise the thickness of nonmagnetic coating materials, such as paint, plastic, porcelain enamel, copper, zinc, aluminum, chrome, and many others. Pretty cut-and-dried if you ask us and before we get down to outlining what makes for a flawless CTG acquisition let’s take a quick gander at the few different but basic measurement techniques inherent in the manifold models available on the market at the moment.

So How many Techniques are There for Appraising the CT in Its Entirety?

To make a long story short, there are two kinds of approaches to measuring CT, – destructive (where it is cut to the substrate using a cutter) and nondestructive (which leaves its surface intact and is in general use in most walks of life today). That’s the long and the short of it!

The Key difference between various CTG Models is Defined By Their Functionality

It’s no surprise that in the current highly-computerized day and age most CTGs come in digital form. However, the importance of mechanical variations can’t be overstated. If you are planning to use your device in any kind of hazardous atmosphere either on land or underwater that has too much or too little oxygen, is rich in easily ignitable, combustible or explosive agents or where high temperatures are prevalent, it’s absolutely imperative you apply a mechanical CTG only; since the entire concept of electricity and hazardous environment don’t exactly gel with each other. When it comes to mechanical gauges the ubiquitous “Banana-Gauge” is the prime example.

What puts Digital Devices into a Separate Category?

coating thickness gauge photo

Digital models are a different story entirely. They are electricity powered and have much broader functionality. Their operation depends totally on what kind of material (magnetic or non-magnetic) serves as a substrate and what kind of coating (magnetic or non-conductive) is being measured. Permanent magnet and magnetic induction CTGs are used to measure the thickness of a nonmagnetic coating on magnetic substrates. Eddy Current CTGs are used to measure the thickness of non-conductive coatings on non-magnetic metal substrates. We know, we know, the terminology can throw some for a loop, but we are only laying the necessary groundwork here.

There are also ultrasonic units that calculate the data based on the speed of the sound through the tested sample, but while they carry a number of benefits over their mechanical and digital counterparts, they are mostly confined to manufacturing applications. Purchasing one for your basic coating appraisal would be a financial overkill. 

There are a few things that need to be said about the be-all and end-all of any high-quality CTG – accuracy, as well as the next most important factor – calibration.

The Accuracy Factor Overrides Everything Else

The degree of accuracy your target model provides will largely determine the amount of money you’ll have to cough up. More expensive units provide laser-like precision, cheaper alternatives allow for different margins of error. If unerring precision is an absolute necessity in your line of work than buying a more expensive product and consistently testing it against preset standards is a must! There are two basic types of CT standards:

Calibration-foils – an array of individual precision foils and foil sets; and precoated metal, which is basically a calibration set from aluminum, steel, iron (etc) plates. These sets often come as part of a package deal when you purchase your CTG. For lack of these, you might want to purchase one separately.

Why is Correct Calibration of Paramount Importance?

Different coatings and substrates have different conductivity and require different calibration to give a correct reading. Surface condition, profile, roughness as well as multiple other outside influences all need to be factored in for a more impeccable eventual reading. For instance, If you work in an area with likely outside magnetic field interference or increased atmosphere temperature – your calibration must be adjusted to that. Present-day digital products have a broad range of values stored in the memory bank, so you won’t encounter any difficulty in tackling any kind of tough coating adversary that happens along. With the small but necessary chemistry lesson in the books, let’s scope out all the possibilities before you decide on a specific model.

Buyers Guide


First off, realistically establish your financial status quo. On average, run of the mill CTG with a customary array of options can set you back $50-150. You won’t get a decent professional one for anywhere less than $350-400.


This might raise a few eyebrows but if you are planning to use your CTG a lot, then a wide, high-definition, high-contrast backlit liquid crystal display is vital. It enables you to read your readouts at all angles and in various environments. A common grievance among users operating lower-priced models is they can’t make heads or tails out of their readings in broad daylight.

Accuracy and Consistency

Make sure the device gives out accurate digits on all kinds of surfaces, including smooth, rough, thin and curved. Getting consistent and repeatable CTM’s is a must for any foolproof CTG.

Auto Options

It would be a good idea to purchase an item that takes at least a part of the manual operation burden off your shoulders and into the automatic realm. The basic auto functions to have are:

Automatic shutdown – your battery will appreciate it.

Automatic recognition of magnetic and nonmagnetic substrates (models that don’t have this function come with a Fe or NFe probes – an extra inconvenience you could do without).

Auto rotatable display – this option is a lifesaver when you work in cramped spaces.

Automatic temperature compensation – this function is a must-have to obtain accurate readings in the desert, alpine conditions or anywhere where serious temperature fluctuations are a factor.

User-programmable high and low limit alarms.

Why is Getting a Quick on The Trigger Gadget Vital?

Most CTGs come equipped with three measurement units (mils, um or mm), however, the rate of work is a much more important spec – the quicker it is the better. Some models seem to take an eternity to refresh, which is a major pain in the neck when time is of the essence.

Calibration Options

Getting a model with an included calibration set would be a good idea, especially if you plan to use it a lot on various substrates and coatings. It’ll give you a chance to recalibrate your device at will. Having a zero and multi-points calibration option is essential to obtain higher overall measurement precision.

Basic Parameters

Basic parameters on any CTG are measuring range, accuracy, and resolution. They in their entirety define the overall functionality of the model in question. In comparative terms, a cheaper 60-70 bucks model gives you a measuring range of 1.5 up to 2 millimeters, allows for a plus/minus 2 to 4 percent margin of error, and provides for a 0.01 mils resolution (resolution is the ability of the measurement system to detect and faithfully indicate small changes in the characteristic of the measurement result). A lower-tier professional upgrade (350 bucks) has a 0.1 to 0.2-inch measuring range and admits of a 0 to 2 percent margin of error, all of which leads to many higher-precision measurements.


Taking your measurements in tight spaces can be an uphill battle and some models are specially designed to remedy that. They come with a wide range of flexible probes of different lengths that can negotiate deep and narrow recesses your ordinary hand-held device could never reach.

Special Features

Here are some extra features that could come in handy as an added bonus:

Increased reading resolution for thin coatings.

Larger sized buttons (key when you are working with your gloves on)

Low battery and an error indicator.

USB port for data transmission.

A shockproof case for carrying and storage.

See also: The Best Laser Measuring Tools

Instruction Manual

When purchasing a foreign-made product make sure it comes with a detailed, totally legible instruction manual, as some offers on the market do seem to be grievously inadequate in this regard.