How to use equilibrium moisture content
What this calculation does
Equilibrium moisture content estimates the level wood may approach under the entered air temperature and relative humidity.
Enter the surrounding air temperature in Fahrenheit and relative humidity as a percentage within the displayed range.
Enter the measurements
- Air temperature: Use air temperature in degrees Fahrenheit.
- Relative humidity: Enter relative humidity as a percentage, not a fraction.
Formula and variables
EMC = 1800/W × [Kh/(1−Kh) + (K1Kh+2K1K2K²h²)/(1+K1Kh+K1K2K²h²)]. h=RH/100; W=330+0.452T+0.00415T²; K=0.791+0.000463T−0.000000844T²; K1=6.34+0.000775T−0.0000935T²; K2=1.09+0.0284T−0.0000904T²; T in °F.
The calculator applies the cited FPL Eq. 4-5 model: temperature determines W, K, K1 and K2, while h is relative humidity divided by 100.
Read the result
At 70°F and 50% RH, the model estimates about 9.246% EMC; this is not a measurement of the current board.
Worked example
Inputs: 70°F and 50% RH
- Set h = 50÷100 = 0.5 and T = 70°F in the stated FPL coefficients.
- Substitution in Eq. 4-5 gives about 9.2463%, displayed as 9.246%.
Expected result: about 9.2% EMC
Frequently asked questions
Is EMC the board’s measured moisture content?
No. It is an equilibrium estimate for the entered conditions; actual wood may differ.
Why are some temperature and humidity values unavailable?
The calculator follows the practical range recorded for this model and does not extrapolate beyond it.
Conditions, presets and technical notes
The practical input range is 30–210°F and 5–95% RH. This estimates equilibrium moisture content, not current board moisture content. Species variation and hysteresis apply; the alternative model is not mixed into this estimate.