How Does a Moisture Meter Work?

How Does a Moisture Meter Work

Spotting mildew and mold in your own home is perhaps a nightmare. Their presence is certainly an indication of other issues cropping in the structure of your home.

So, is there any way to prevent their occurrence? Well, there is a way; it is of using a moisture meter.

How does moisture meter work? A moisture meter works in different ways to compute the amount of moisture on the surface of the target substance. It uses pins, electric currents, radio waves, reagents, probes, mirrors, or silicone or aluminum oxides.

More and more people are using a moisture meter for this reason. It is a clever device that measures the amount of water or liquid in materials such as paper and wood. This result is useful in determining how damp material is.

Subsequently, you can decide whether the material is ready for use or needs further inspection. Paper and wood items are highly sensitive to moisture content. This content heavily influences their physical properties. High moisture content for a few months can gradually degrade a material.

While several people use these devices for gauging the wood’s water content, a few models work efficiently even on drywall and concrete surfaces. Unfortunately, moisture is found even in surfaces which we consider as dry.

This is exactly why you should have a moisture meter. It is a versatile device that contractors and DIYers use prior to woodworking. So, how do they work to calculate the moisture level? Let’s find out!

MY TOP Moisture Meter Pick:

If you are looking for a good overall moisture meter, I recommend the General Tools MMD4E Digital Moisture Meter (you can check Amazon), because it features an easy-to-read LCD display for quick and easy viewing. It gives you an instant reading of moisture if you stick it in any piece of wood.

Types of Moisture Meters

There is no standard or single mechanism using which moisture meters work. As they can measure a variety of materials, they are available in different styles and use different measurement technologies.

The style indicates the purpose. Considering the relation between the style, application, and measuring technology, these devices are of two types namely, handheld or fixed mounts.

Handheld Moisture Meters

These meters are highly portable and are useful for measuring the level of moisture in building materials, soils, and agricultural products such as bulk grains. Four types of handheld versions exist, which are as follows:


How Does a Pin-Type Moisture Meter Work? These devices employ an invasive mechanism to gauge the moisture level. They come with a pair of pins that are pushed into the material under investigation. As pins go inside the material, they are likely to result in surface damage.

Thus, it is wise to test at the back of the material. These meters work on the basis of electrical resistance. When the pins penetrate the material, an electrical current is passed.

The amount of moisture is inversely proportional to the amount of resistance. As moisture is a good conductor of electricity, its high level means a low material resistance value.

The resulting measurements are affected by the differences in the naturally-occurring composition of woods.

Thus, these moisture meters are typically calibrated for specific woods. As pin-type devices inspect a very small area, they are subject to moisture fluctuations present in a sample.


These meters are non-invasive tools and employ a myriad of gauging methods without damaging the material surface. They emit electromagnetic waves, typically an electric current or radio waves, for gauging moisture.

The presence of moisture influences these waves. By sensing how the returning wave is influenced, the amount of moisture is calculated. In the case of an electrical current, the computation is based on the principle that a material’s resistance is low if the moisture content is high.

In the case of radio waves, the waves’ characteristics help in computing the moisture content on a relative scale and not as a percentage. Unlike the pin-type counterparts, pin-less meters can measure a large surface area.

They can even scan the wood to give you a full moisture profile. However, their reading depth is confined to around 1/4 – 3/4 inches and that they are highly susceptible to surface moisture.


These meters are rarely seen. They use reagents to gauge moisture. They typically grind a test sample and combine the same with a reagent that responds to moisture by generating the gas.

It also results in more pressure inside the unit of testing, which increases in proportion to the sample’s moisture amount. By gauging this rise in pressure, it computes the amount of moisture.


These units come with an outlet to which a probe is attached. Such a setup is seen in a few pin-type and pin-less meters. Probes are versatile for testing some specific solid areas, such as within a bale of hay, instead of testing only near the surface.

They work by implementing capacitive polymer sensing or conductivity. The latter meters work similarly to the pin-type meters in which a small electrical charge moves from one point to another.

On the other hand, capacitive polymers sensors work based on the capacitor’s electrical traits. A capacitor features two conductive plates separated via a dielectric. A thin polymer hygroscopic layer as the dielectric absorbs the moisture. Its conductivity changes proportionally to the present amount of moisture.

Fixed Mount Meters

As the name indicates, these meters remain fixed in place for measuring moisture levels in hydrocarbon liquids or gases.

For investigating these substances, much different technology than those for solids is employed. Following are the types of fixed mount moisture meters:

Chilled Mirrors

These devices operate on the principle that moisture condenses on a mirror when gas flows over it (cool surface). This condensation starts at the dew point and is detected using optical or visual mechanisms.

The mirror’s temperature goes down and the temperature is read when the dew is seen. By fetching the dew point temperature, it is possible to compute the gas’ moisture content. A refrigerant’s flow over the mirror controls the chilled mirror’s temperature.

Silicone/Aluminum Oxide Sensors

These devices are analogous to capacitive moisture sensors in terms of design. They are built using an inert substrate such as aluminum or silicon that is oxidized.

To this, a layer of gold is added through the process of chemical vapor deposition. The aluminum and gold act as a capacitor’s electrodes.

When water vapor passes over the gold layer, it is absorbed by the oxide’s pore walls until equilibrium.

Moisture Content Sensor

For long term monitoring of moisture content in wood frames to detect mold or decay, it is common to measure the resistance of wood and convert that to a moisture content reading.

How Does A Moisture Meter Work Video


Leave a Comment