Wood Moisture Equilibrium Calculator

Calculate the Equilibrium Moisture Content (EMC) of wood from temperature and humidity using the Hailwood-Horrobin equation, plus dimensional change and acclimation time.

Inputs

Temperature (F)

Relative humidity (%)

Current wood MC (%)

Board thickness (in)

Board width (in)

Tangential shrinkage %/MC% (0=avg)

Tab to move between fields

Results

Equilibrium MC (%)

9.2

MC change needed (%)

2.8

Current MC (%)12

Width change (in)0.05

Dimensional change (%)0.77

Estimated acclimation (days)17

Interior furniture target MC (%)7

EMC vs interior target (%)2.2

Risk LevelModerate — allow full acclimation

How to Use This Calculator

Enter the ambient Temperature in °F and Relative Humidity percentage where the wood will be installed.
Enter the Current Wood Moisture Content from a moisture meter reading.
Enter the Board Thickness and Width in inches for dimensional change calculations.
Review Equilibrium MC to know the target moisture content and MC Change needed.
Check Width Change in inches and Acclimation Days to plan proper wood conditioning before construction.

How the result changes with Relative humidity (%)

Relative humidity (%)	Equilibrium MC (%)	MC change needed (%)
14	3.3	8.7
38	7.4	4.6
66	12.2	-0.2
90	20.5	-8.5

What each input means

Temperature (F): Ambient air temperature in Fahrenheit where the wood will live.
Relative humidity (%): Average relative humidity of the environment.
Current wood MC (%): Current moisture content of the lumber (from a moisture meter).
Board thickness (in): Thickness of the stock. Thicker boards take longer to acclimate.
Board width (in): Width of the board for dimensional change estimation.
Tangential shrinkage %/MC% (0=avg): Species tangential shrinkage per 1% MC change. Oak ~0.37, Cherry ~0.25, Pine ~0.22. Enter 0 for average hardwood.

What each result means

Equilibrium MC (%): The moisture content the wood will reach at the given temperature and humidity.
Current MC (%): Your entered current moisture content.
MC change needed (%): Positive = wood needs to lose moisture; negative = wood needs to gain moisture.
Width change (in): Expected tangential dimensional change across the board width.
Dimensional change (%): Percentage width change from current MC to EMC.
Estimated acclimation (days): Approximate days to reach EMC in a conditioned shop.
Interior furniture target MC (%): Standard target MC for indoor furniture (6-8%).
EMC vs interior target (%): How far the EMC is from the ideal interior furniture MC of 7%.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Temperature (F) = 70, Relative humidity (%) = 50, Current wood MC (%) = 12, Board thickness (in) = 0.75 = 6 input(s) provided
Calculate Equilibrium MC
Equilibrium MC = max(2, min(30, EMC))
9.2 = 9.2
Calculate MC change needed
MC change needed = currentMC - emcClamped
2.8 = 2.8
Calculate Current MC
Current MC
12 = 12
Calculate Width change
Width change = Math
0.046 = 0.046

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