History of Wood Moisture Meters

Even before the science of wood’s relationship with moisture was well-understood, woodworkers had to factor in how moisture would affect their materials.

Today, we understand the hygroscopic properties of wood well, and that knowledge has made it possible to design wood moisture meters that give us measurable data about a piece of wood’s moisture condition. As our collective understanding has advanced, the testing methods have evolved as well.

Today, there are two main types of hand-held wood moisture meters: pin and pinless. Each relies on different electrical properties that are impacted by the amount of moisture held in the wood being measured, which we’ll explore in detail later in this article.

For now, it’s enough to say that pin-type meters use two nail-like electrodes that get inserted into the wood and measure the current that flows between them. Pinless meters use sensor plates that lie flat on the wood’s surface and measure the behavior of an electromagnetic wave they send into the wood.

Without getting into the science of each moisture meter type, the most apparent differences between them are what they do to the wood being measured, and how easy they are to use.

Pin meters leave holes in the wood being measured. This makes them useful for evaluating the moisture content of firewood or pieces of wood where leaving multiple holes won’t negatively impact the structural integrity or aesthetics of the final product.

In contrast, pinless meters don’t leave any physical markers behind. They can only be used on flat wood, and the whole sensor needs to stay in contact with the wood during a reading.

Having to insert or hammer in pins also makes pin meters slower to use. Inserting the pins to the right depth, removing them, and ensuring the pins remain in good condition to take a reading takes time.

Consequently, when having to assess the moisture condition of a large piece or large batch of wood, you have to invest a significant amount of time. The more likely scenario is that you’ll simply take fewer readings. One extends project timelines and costs, while the other means you’ll be making decisions with fewer data points guiding you.

You can work much more efficiently with pinless meters, since they take less physical effort and aren’t as vulnerable to damage as pin electrodes.

But this is where we are today. Electric moisture meters have nearly a 100-year history. Interestingly, they still rely on an even older method, oven drying, to validate their accuracy. To appreciate how hand-held wood moisture meters of today operate, it’s worth digging into the evolution of the technology on which they rely.

Oven-Dry Methods Are the Gold Standard for Measuring Wood Moisture

The earliest method used to dry wood is air drying or “weather drying.” That takes time. Wood would often be left for years before being used. Early attempts to speed up the drying process resulted in various types of “dry-houses” being built. These were simple structures set over dugout cellars holding a brick or tile furnace.

In the United States, the use of “dry-houses” wasn’t the norm, in part because they presented enormous fire risk. There was some experimentation using steam pipes in the 1850s, but it didn’t go well. Eventually, the first successful wood drying kilns, drying chambers that had some thermal insulation, were popping up around the Midwest in the 1870s.

Through trial and error, kiln operators discovered that drying wood at lower temperatures with circulating air produced better results than turning the heat on high. Eventually, the trial and error approach by businesses seeking to minimize drying times while maximizing outputs got assistance from the scientists and researchers. Through scientific inquiry, researchers began discovering and validating a wide range of physical properties of wood. Some of their discoveries included understanding the cellular structure and chemical properties of wood.

In turn, this led to understanding how physical differences among wood species, and even among the same species grown in different locations, impact the drying process of the wood.

Through the rise of wood research, wood scientists developed a formula for specifying the moisture content of a piece of wood as a function of its weight and expressed as a percentage.

Moisture content (MC) = (wet weight − oven-dry weight) ÷ oven-dry weight × 100

As such, the oven-dry method provides a direct measurement of a piece of wood’s moisture content. If you have a wood-drying oven, you can weigh the wood both before and after it’s run through a drying cycle in the oven. ASTM D4442 (standard test method for direct moisture content measurement of wood and wood-based materials) states that oven-drying provides “the highest accuracy or degree of precision” and is “the reference (primary) standard for determining the moisture content of wood and wood-based materials.”

As a result, oven drying wood in compliance with ASTM D4442 is used as the reference point for calibrating hand-held moisture meters per ASTM D4444 (standard test method for laboratory standardization and calibration of hand-held moisture meters).

Hand-held moisture meters provide an indirect measure of moisture. Since water conducts electricity, the hand-held meters collect data about the behavior of electric currents or waves in a piece of wood. This data is then used, along with other relevant data points, to calculate the wood’s moisture content.

Evolution of Electric Wood Moisture Meters

Humanity has long understood that wood contains moisture; that it dries out and can reabsorb moisture when in contact with water. In truth, scientists have also known about the relationship between water and electricity from nearly the moment electricity was discovered. Specifically, they knew that water conducts electricity, even if the specific chemical process that occurs in water as it allows electrical charges to pass through it has been more recently documented.

Researchers first showed in the late 1920s that the electrical properties of wood could be used to measure its moisture content. One of the first documented portable electric wood moisture meters was a “blinker-type” meter in 1927. This meter had a neon lamp attached to a capacitor, which was in contact with the wood. The capacitor would absorb the charge running through the wood. When the capacitor was fully charged, the neon lamp would briefly light up. The faster the capacitor could recharge, the faster the lamp would blink.

How quickly the capacitor could recharge was a function of how much resistance was in the wood. Since moisture conducts electricity, the more moisture in the wood, the faster the capacitor would reach a full charge. If the wood had high resistance (low moisture), the lamp would blink slowly.

Within the following ten years, a new type of electric moisture meter was developed: a vacuum tube meter. This meter used a vacuum tube voltmeter as part of a Wheatstone bridge circuit, which uses a resistor to measure against the wood being measured. The vacuum tube meter is the direct precursor to the resistance moisture meters used today.

By the mid-1940s, pin-type meters were commercially available. They worked (and still do) by measuring the flow of an electric current between probes inserted into the wood. As with the early blinker-type meter, more current flowing between the probes meant more moisture in the wood.

Dry wood, without much moisture to conduct electricity, has such high resistance that very little current flows. Some early pin meters used four probes. Modern pin type moisture meters require only two probes.

During this period when resistance meters were hitting the market, researchers were also exploring how dielectric properties could be used to measure moisture in wood. Dielectric materials are insulators, but an electric field can still pass through them and polarize them. This research ultimately resulted in two other types of wood moisture testing methods that work on two different dielectric principles.

Without diving too deeply into electrical engineering, these two types of dielectric meters used radio waves to measure moisture levels. The power-loss type of meter looks at how much electromagnetic energy is lost, which correlates to moisture levels. The capacitance moisture meter looks instead at how much electrical energy the wood can store. What they have in common, on a practical level, is that neither requires pins to break through the wood’s surface.

Instead, they use sensor plates that emit a radio frequency through the wood. The USDA Forest Service’s Forest Products Laboratory (FPL) had developed a capacitance-type machine to measure wood moisture, but it wasn’t commercially available. By this time, many manufacturers were selling pin-style moisture meters.

The Modern Era of Electric Wood Moisture Meters

By the early 1960s, there was one common power-loss type moisture meter on the market. During this period, Delmer Wagner, the founder of Wagner Meters, was working at a sawmill in Redmond, Oregon. Like other mills, it used a large, unwieldy moisture detector built with vacuum tubes.

In 1963, Delmer developed the first in-line moisture detector to use transistors, which made it smaller, more reliable, and easier to calibrate. In 1965, he founded Wagner Electronics (known today as Wagner Meters), which built in-line moisture meters for the lumber industry.

For decades, nearly all handheld wood moisture meters were pin meters. The pinless meters available were large, hard to calibrate, and too sensitive to ambient conditions, so the pin meter market thrived while there were very few pinless meters.

Wagner introduced its first pinless wood moisture meter, the L600, in 1980. Its pinless meters use electromagnetic wave technology and are less sensitive to ambient and wood temperature. In the early 1990s, Wagner developed smaller handheld pinless meters designed for wood flooring and woodworking customers who needed to scan lumber quickly.

Later Wagner meters added digital displays and microprocessors, and the meters kept getting smaller. Accuracy studies have found that Wagner’s pinless meters can deliver more accurate readings than pin meters, which challenges the common assumption that pin meters are more accurate.

The fundamental technologies used in both pin-style and pinless meters remain unchanged. Today, most advances in wood moisture meters are focused on the value-added features embedded in the meters and related services.

Wagner’s Orion^® line of wood moisture meters includes features that make woodworkers’ lives easier.

For example, Orion meters can be calibrated on-site with the On-Demand Calibrator that comes with each meter, instead of being sent back to the factory for recalibration, which costs time and money.

Some of the most useful value-added features improve the meter’s data collection and management. Knowing the equilibrium moisture content (EMC) for the location where the wood will be used is vital to preventing moisture damage, so the Orion 950 calculates EMC for you.

The meter takes an ambient temperature and relative humidity reading and uses it to calculate EMC. That EMC can then be used as the “target moisture content” for the project you’re working on, or be used to predict drying patterns. Moisture meter-based EMC calculations relieve users of the hassle and uncertainty of calculating EMC themselves.

Pinless Meters Prove More Accurate and Reliable than Pin-type Moisture Meters

Pin and pinless moisture meters both rely on the electrical properties of wood, but they measure different ones. Put simply, pin meter readings are affected by the wood’s chemical makeup, and pinless meter readings are affected by its density (specific gravity).

Both chemical makeup and density vary by species. This is the reason why both meters require adjustment for the species being measured to get an accurate moisture reading.

According to the FPL, some of the issues that impact the accuracy of a meter reading are weather conditions, electrode contact, wood temperature, and the skill of the operator. Many of these issues affect pin type moisture meters more readily than they do pinless meters. Studies have shown that pinless meters are often more accurate and reliable than pin (resistance) meters.

For instance, pin meters are highly sensitive to wood temperature. When the wood is much warmer or cooler than about 70°F, the operator has to correct the readings for the wood’s temperature.

Making wood temperature adjustments is only one way where the subjective skill of the meter operator can impact a pin meter’s accuracy. Pin meters also require precise operator skill to ensure both electrodes are correctly driven into the wood and to the right depth. Without proper alignment or depth, the electrodes may not measure moisture accurately for that spot’s moisture level.

The most critical operator skill in placing a pinless moisture meter is simply to ensure that the sensor plates lay flat on the wood’s surface.

That’s why pinless meters aren’t typically used on firewood or other rough, uneven wood. Otherwise, because pinless meters are so fast and easy to use, woodworkers usually take more readings with them than with pin meters, and more readings give a more accurate picture of a batch of wood’s moisture condition.

The History of Wood Moisture Meters: From Trial and Error to an Essential Woodworking Tool

As the lumber industry grew apace with the industrial revolution during the 19th century, it’s logical that lumber mills sought ways to speed up the drying process in ways that didn’t destroy the wood. Their trial and error methodology, along with their anecdotal knowledge of weather drying, helped them innovate.

They realized how circulating air helped maximize outputs by allowing for lower temperatures to be used to dry lumber. They saw how different wood species reacted under similar circumstances. Their practical explorations were the foundation of formalized wood science.

Through the rigors of scientific and academic inquiry, our understanding of wood’s physical and mechanical properties expanded significantly throughout the 20th century. Through this research, the industry has been able to specify how moisture moves through wood and how excessive moisture negatively affects wood.

Coming full circle, the lumber industry has used wood science contributions to develop the tools needed to measure the moisture content of wood, both directly and indirectly, with a high degree of accuracy.

As wood science revealed more about the interplay of moisture and electricity in wood, meter manufacturers used those advances to build commercially viable moisture meters, especially handheld meters.

With reliable and accurate hand-held wood moisture meters, every woodworker, from the operator of a lumber mill to the weekend hobbyist, has the ability to make informed decisions about when wood is ready to take the next step in its journey towards its intended use. Wood moisture meters have become a staple for many woodworkers, and now that accurate moisture information is this easy to get, there’s little reason to work without it.

Shop Orion Moisture Meters

Last updated on October 9th, 2026