### Calculator (Celsius)

Average Annual Outdoor Temperature (Degrees Celsius)
Average Annual Outdoor Relative Humidity (Percent)
AWI Climate Zone
Optimum Climate-Controlled Moisture Content
Optimum Climate-Controlled Relative Humidty
Average Non-Climate-Controlled Equilibrium Moisture Content

### Calculator (Celsius)

Average Annual Outdoor Temperature (Degrees Fahrenheit)
Average Annual Outdoor Relative Humidity (Percent)
AWI Climate Zone
Optimum Climate-Controlled Moisture Content
Optimum Climate-Controlled Relative Humidty
Average Non-Climate-Controlled Equilibrium Moisture Content

This calculator is provided for ease of reference and convenience. The values produced by this calculator should not be used without independent calculation and verification.

This calculator assumes climate-controlled temperatures of 15.5–32°C [60–90°F] and compares a given project location's outdoor climate conditions to the USDA Forest Products Laboratory's data on equilibrium moisture content averages. This defines a range of optimum climate-controlled relative humidity and moisture content levels for the maintenance of architectural woodwork. It then suggests which AWI Climate Zone your project is likely to fall into based on the calculated values.

### Equilibrium Moisture Content

Equilibrium Moisture Content is a measure of the moisture content of wood held in an environment with a consistent temperature and relative humidity for such a period of time that the moisture content stabilizes.

The non-climate-controlled values generated by this calculator are based on the data and formulas published by the USDA Forest Products Laboratory's "Equilibrium Moisture Content of Wood in Outdoor Locations in the United States and Worldwide" and provide a range of possible EMC values for wood and wood products in outdoor or non-climate controlled environments for which ranges of average temperatures and realtive humidity levels are known.

The formula used for calculating EMC is:

$$\small{EMC = {1,800 \over W} \Biggl( {Kh \over 1-Kh}+{{K_1Kh+2K_1K_2K^2h^2} \over {1+K_1Kh+K_1K_2K^2h^2}} \Biggr)}$$

For temperatures in Celsius,

$$W = 349 + 1.29T + 0.0135T^2$$

$$K = 0.805 + 0.000736T - 0.00000273T^2$$

$$K_1 = 6.27 - 0.00938T - 0.000303T^2$$

$$K_2 = 1.91 + 0.0407T - 0.000293T^2$$

For temperatures in Fahrenheit,

$$W = 330 + 0.452T + 0.00415T^2$$

$$K = 0.791 + 0.000463T - 0.000000844T^2$$

$$K_1 = 6.34 + 0.000775T - 0.0000935T^2$$

$$K_2 = 1.09 + 0.0284T - 0.0000904T^2$$

where T is temperature, h is relative humidity (%/100), EMC is moisture content (%), and W, K, K1, and K2 are coefficients of an absorption model developed by Hailwood and Horrobin (1946).