EMC—what is it and why does it matter?

What is equilibrium moisture content, and how could ignoring it potentially ruin your wood projects?

If you want the answer, keep reading.

What is EMC?

Equilibrium moisture content is the point at which a wood board neither gains nor loses moisture.

Wood is a hygroscopic material, meaning that it will expand or contract based on how much moisture is in its environment, reaching EMC is important to keep your projects from moisture-related damage.

When the moisture content of the environment, such as the amount of humidity in the air, is equal to the moisture content of the wood plank, then the planks have reached EMC.

It will fluctuate throughout the year. Whenever the temperature changes or the humidity changes, the EMC also changes. In fact, where you live will greatly impact the equilibrium moisture content.

If you live in a climate where the weather doesn’t change much year-round, your EMC will probably remain somewhat stable.

If you live somewhere with a lot of seasonal climate variability, then the EMC will change with the seasons.

Being aware of these changes and pinpointing the equilibrium between the environment and wood is very important. Wonder why?

Let’s find out in the next section.

Blue wooden planks with gaps and cracks as we discuss the issues we run into if we have not taken Equilibrium Moisture Content or EMC into consideration.

Why is the EMC Important for Your Wood Projects?

Understanding EMC is crucial to achieving success in your wood projects because if not, you might experience significant moisture-related problems.

For example, if you are installing a floor and haven’t taken EMC into consideration, your boards might shrink or swell more than you expected.

This can lead to issues like buckling, cupping, crowning, gapping, warping, and cracking, which will, in turn, compromise the wood’s structural integrity, cause more headaches, and cost more money in the long run.

Needless to say, knowing the EMC of a given area and the moisture content of your wood is important for several reasons. Because it varies based on your location, you will want to have the ability to check EMC and moisture content quickly, accurately, and easily, which brings us to our next point…

How is Equilibrium Moisture Content Measured?

Several mathematical formulas have been developed to calculate EMC. This equation provides a reasonable estimation of EMC:

EMC = [-ln (1-ϕ) / 4.5 x 10^-5 (T + 460)] ^ 0.638


ln = natural logarithm (a mathematical equation that calculates the time it takes to reach a specified point)
ϕ = relative humidity expressed as a decimal
T = temperature in Fahrenheit


The use of equations like this can be complicated and time-consuming.

The best option is to find an EMC chart specific to your region.

Then, you can use a pinless moisture meter, like those from Bessemeter, to determine how close–or how far–your wood project is to reaching EMC.

With a Bessemeter pinless moisture meter in hand, you won’t have to fear moisture-related failures because you’ll have the information you need to make wise woodworking decisions.

Let’s look at some of the factors that affect EMC.

What Influences EMC?

Two affecting factors:

  • Humidity
  • Temperature


Thermometer for wood, as we learn how changes in temperature indirectly influences Equilibrium Moisture Content or EMC by affecting the relative humidity.Humidity is, essentially, a measure of the amount of water in the air at a given temperature. This has the greatest impact on how quickly–or slowly–wood will reach EMC. The higher the humidity, the more difficult it will be for the wood to dry sufficiently. At high humidity, the wood will tend to absorb moisture from the air instead of releasing moisture.


Temperature indirectly influences EMC by affecting the relative humidity of the service location. Simply put, lowering or raising the temperature impacts how much water vapor that the air can hold–which impacts the relative humidity. For example, if the temperature were to go down, this would lead to an increase in RH and the wood would tend to respond by absorbing additional moisture to reach EMC. Essentially, temperature can impact whether the wood is absorbing or releasing moisture.

How to Keep Your Wood Projects from Moisture-Related Failure

Not understanding EMC is risky when it comes to working with wood, but now that you’ve read this page, you’ve taken a great step towards guarding yourself against moisture damage in your wood projects.

Take your knowledge a step further by purchasing a Bessemeter pinless moisture meter. With a moisture meter to quickly and easily measure the wood’s moisture content, you can protect your projects from failure and protect yourself from spending time and money unnecessarily. Check out our product page for more information!