Equilibrium Moisture Content Calculator for Wood (EMC)

Wood trades moisture with the air around it until it reaches a balance, its equilibrium moisture content (EMC). Enter the temperature and relative humidity of the room, shop or storage area and this calculator gives the EMC from the sorption equation in the USDA Wood Handbook, then compares it with the Handbook’s recommended moisture contents for interior and exterior wood. Below the calculator are an EMC chart and the Handbook’s monthly outdoor EMC for 49 US cities.

Wood equilibrium moisture content calculator

How it works

The Handbook models sorption with the Hailwood-Horrobin equation (Eq. 4-5), with T in degrees Celsius and h the relative humidity as a fraction:

M = (1,800 / W) × [Kh / (1 − Kh) + (K₁Kh + 2K₁K₂K²h²) / (1 + K₁Kh + K₁K₂K²h²)]
W = 349 + 1.29T + 0.0135T²
K = 0.805 + 0.000736T − 0.00000273T²
K₁ = 6.27 − 0.00938T − 0.000303T²
K₂ = 1.91 + 0.0407T − 0.000293T²

The equation was fitted to data for Sitka spruce under conditions between gaining and losing moisture, and the Handbook uses it for all species: the EMC of different woods at the same conditions is close enough for practical use. Relative humidity matters far more than temperature.

Worked example

A heated workshop at 70 °F with the hygrometer reading 45% relative humidity:

Temperature unit: Fahrenheit
Air temperature: 70
Relative humidity: 45%

The calculator gives:

Equilibrium moisture content: 8.5%
Compared with installation targets: inside the 6 to 10% range recommended for interior woodwork, flooring and furniture in most of the US
Temperature used: 21.1 C (70 F)

Wood kept in that shop will settle at about 8.5% moisture content, inside the 6 to 10% range the Handbook recommends for furniture, flooring and interior trim in most of the United States (average 8%). Lumber brought in at 12% from an open shed will shrink as it dries toward 8.5%, so let it acclimate before final dimensioning. At 70 °F and 50% the equation gives 9.2%, the same value as the Handbook’s Table 4-2.

Equilibrium moisture content chart (°F)

Temp	10% RH	20% RH	30% RH	40% RH	50% RH	60% RH	70% RH	80% RH	90% RH
30 °F	2.6	4.6	6.3	7.9	9.5	11.3	13.6	16.5	21
40 °F	2.6	4.6	6.3	7.9	9.5	11.3	13.5	16.5	21
50 °F	2.6	4.6	6.3	7.9	9.5	11.2	13.4	16.4	20.9
60 °F	2.5	4.6	6.3	7.8	9.4	11.1	13.3	16.2	20.7
70 °F	2.5	4.5	6.2	7.7	9.2	11	13.1	16	20.5
80 °F	2.4	4.4	6.1	7.6	9.1	10.8	12.9	15.7	20.2
90 °F	2.3	4.3	5.9	7.4	8.9	10.5	12.6	15.4	19.9
100 °F	2.3	4.2	5.8	7.2	8.7	10.3	12.3	15.1	19.5

Wood moisture content (%) from Wood Handbook Eq. 4-5. Rows are air temperature, columns relative humidity.

Use	Most of the US	Dry southwest	Damp, warm coast
Interior: woodwork, flooring, furniture, trim	8% (6 to 10%)	6% (4 to 9%)	11% (8 to 13%)
Exterior: siding, trim, sheathing, laminated timbers	12% (9 to 14%)	9% (7 to 12%)	12% (9 to 14%)

Outdoor equilibrium moisture content by city and month

City	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Avg
Juneau, AK	16.5	16	15.1	13.9	13.6	13.9	15.1	16.5	18.1	18	17.7	18.1	16
Mobile, AL	13.8	13.1	13.3	13.3	13.4	13.3	14.2	14.4	13.9	13	13.7	14	13.6
Flagstaff, AZ	11.8	11.4	10.8	9.3	8.8	7.5	9.7	11.1	10.3	10.1	10.8	11.8	10.3
Phoenix, AZ	9.4	8.4	7.9	6.1	5.1	4.6	6.2	6.9	6.9	7	8.2	9.5	7.2
Little Rock, AR	13.8	13.2	12.8	13.1	13.7	13.1	13.3	13.5	13.9	13.1	13.5	13.9	13.4
Fresno, CA	16.4	14.1	12.6	10.6	9.1	8.2	7.8	8.4	9.2	10.3	13.4	16.6	11.4
Los Angeles, CA	12.2	13	13.8	13.8	14.4	14.8	15	15.1	14.5	13.8	12.4	12.1	13.7
Denver, CO	10.7	10.5	10.2	9.6	10.2	9.6	9.4	9.6	9.5	9.5	11	11	10.1
Washington, DC	11.8	11.5	11.3	11.1	11.6	11.7	11.7	12.3	12.6	12.5	12.2	12.2	11.9
Miami, FL	13.5	13.1	12.8	12.3	12.7	14	13.7	14.1	14.5	13.5	13.9	13.4	13.5
Atlanta, GA	13.3	12.3	12	11.8	12.5	13	13.8	14.2	13.9	13	12.9	13.2	13
Honolulu, HI	13.3	12.8	11.9	11.3	10.8	10.6	10.6	10.7	10.8	11.3	12.1	12.9	11.6
Boise, ID	15.2	13.5	11.1	10	9.7	9	7.3	7.3	8.4	10	13.3	15.2	10.8
Chicago, IL	14.2	13.7	13.4	12.5	12.2	12.4	12.8	13.3	13.3	12.9	14	14.9	13.3
Indianapolis, IN	15.1	14.6	13.8	12.8	13	12.8	13.9	14.5	14.2	13.7	14.8	15.7	14.1
Des Moines, IA	14	13.9	13.3	12.6	12.4	12.6	13.1	13.4	13.7	12.7	13.9	14.9	13.4
Wichita, KS	13.8	13.4	12.4	12.4	13.2	12.5	11.5	11.8	12.6	12.4	13.2	13.9	12.8
Louisville, KY	13.7	13.3	12.6	12	12.8	13	13.3	13.7	14.1	13.3	13.5	13.9	13.3
New Orleans, LA	14.9	14.3	14	14.2	14.1	14.6	15.2	15.3	14.8	14	14.2	15	14.6
Portland, ME	13.1	12.7	12.7	12.1	12.6	13	13	13.4	13.9	13.8	14	13.5	13.2
Boston, MA	11.8	11.6	11.9	11.7	12.2	12.1	11.9	12.5	13.1	12.8	12.6	12.2	12.2
Detroit, MI	14.7	14.1	13.5	12.6	12.3	12.3	12.6	13.3	13.7	13.5	14.4	15.1	13.5
Minneapolis-St. Paul, MN	13.7	13.6	13.3	12	11.9	12.3	12.5	13.2	13.8	13.3	14.3	14.6	13.2
Jackson, MS	15.1	14.4	13.7	13.8	14.1	13.9	14.6	14.6	14.6	14.1	14.3	14.9	14.3
St. Louis, MO	14.5	14.1	13.2	12.4	12.8	12.6	12.9	13.3	13.7	13.1	14	14.9	13.5
Missoula, MT	16.7	15.1	12.8	11.4	11.6	11.7	10.1	9.8	11.3	12.9	16.2	17.6	13.1
Omaha, NE	14	13.8	13	12.1	12.6	12.9	13.3	13.8	14	13	13.9	14.8	13.4
Las Vegas, NV	8.5	7.7	7	5.5	5	4	4.5	5.2	5.3	5.9	7.2	8.4	6.2
Reno, NV	12.3	10.7	9.7	8.8	8.8	8.2	7.7	7.9	8.4	9.4	10.9	12.3	9.6
Albuquerque, NM	10.4	9.3	8	6.9	6.8	6.4	8	8.9	8.7	8.6	9.6	10.7	8.5
New York, NY	12.2	11.9	11.5	11	11.5	11.8	11.8	12.4	12.6	12.3	12.5	12.3	12
Raleigh, NC	12.8	12.1	12.2	11.7	13.1	13.4	13.8	14.5	14.5	13.7	12.9	12.8	13.1
Fargo, ND	14.2	14.6	15.2	12.9	11.9	12.9	13.2	13.2	13.7	13.5	15.2	15.2	13.8
Cleveland, OH	14.6	14.2	13.7	12.6	12.7	12.7	12.8	13.7	13.8	13.3	13.8	14.6	13.5
Oklahoma City, OK	13.2	12.9	12.2	12.1	13.4	13.1	11.7	11.8	12.9	12.3	12.8	13.2	12.6
Pendleton, OR	15.8	14	11.6	10.6	9.9	9.1	7.4	7.7	8.8	11	14.6	16.5	11.4
Portland, OR	16.5	15.3	14.2	13.5	13.1	12.4	11.7	11.9	12.6	15	16.8	17.4	14.2
Philadelphia, PA	12.6	11.9	11.7	11.2	11.8	11.9	12.1	12.4	13	13	12.7	12.7	12.3
Charleston, SC	13.3	12.6	12.5	12.4	12.8	13.5	14.1	14.6	14.5	13.7	13.2	13.2	13.4
Sioux Falls, SD	14.2	14.6	14.2	12.9	12.6	12.8	12.6	13.3	13.6	13	14.6	15.3	13.6
Memphis, TN	13.8	13.1	12.4	12.2	12.7	12.8	13	13.1	13.2	12.5	12.9	13.6	12.9
Dallas-Ft. Worth, TX	13.6	13.1	12.9	13.2	13.9	13	11.6	11.7	12.9	12.8	13.1	13.5	12.9
El Paso, TX	9.6	8.2	7	5.8	6.1	6.3	8.3	9.1	9.3	8.8	9	9.8	8.1
Salt Lake City, UT	14.6	13.2	11.1	10	9.4	8.2	7.1	7.4	8.5	10.3	12.8	14.9	10.6
Richmond, VA	13.2	12.5	12	11.3	12.1	12.4	13	13.7	13.8	13.5	12.8	13	12.8
Seattle-Tacoma, WA	15.6	14.6	15.4	13.7	13	12.7	12.2	12.5	13.5	15.3	16.3	16.5	14.3
Madison, WI	14.5	14.3	14.1	12.8	12.5	12.8	13.4	14.4	14.9	14.1	15.2	15.7	14.1
Charleston, WV	13.7	13	12.1	11.4	12.5	13.3	14.1	14.3	14	13.6	13	13.5	13.2
Cheyenne, WY	10.2	10.4	10.7	10.4	10.8	10.5	9.9	9.9	9.7	9.7	10.6	10.6	10.3

Wood Handbook Table 13-1: EMC (%) for wood exposed outdoors under cover, from 30 or more years of NOAA temperature and humidity records before 1997.

Notes and limits

Use the humidity where the wood will live, not where it is stored. A floor laid in a damp August will shrink in a heated January.
Wood responds slowly: thin boards reach a new EMC in days or weeks, thick timbers in months. The surface changes first, which is why stickered boards can cup.
Kiln-dried lumber sold at 6 to 8% will pick up moisture in a humid shed. Check it with a moisture meter before you build. Air-dried lumber stops at the outdoor EMC; USDA drying times by species are in how long to dry lumber.
Hot-pressed panels such as particleboard and hardboard settle at a lower moisture content than solid wood at the same humidity, so this equation does not apply to them.
Indoor relative humidity swings with the seasons and with heating, air conditioning and humidifiers. Plan for the range, not one reading: compare winter and summer readings in the calculator.

Frequently asked questions

What is the equilibrium moisture content of wood indoors?

In a heated house at 70 °F and 30 to 45% relative humidity, about 6 to 8.5%. The Wood Handbook recommends an average of 8% (6 to 10% for individual pieces) for interior woodwork in most of the United States.

What humidity gives 6% moisture content?

About 30% relative humidity at 70 °F. The calculator gives 6.2% at 70 °F and 30%, and 7.7% at 40%.

What is the EMC at 70 degrees and 50% humidity?

9.2%, which matches Table 4-2 of the Wood Handbook.

Does temperature change the moisture content of wood?

A little. At the same 50% humidity, wood settles at 9.5% at 30 °F and 8.7% at 100 °F. Humidity has a much bigger effect.

What moisture content should lumber be for outdoor use?

About 12% on average in most of the US (9 to 14% for individual pieces), 9% in the dry southwest, per Handbook Table 13-2.

Sources

Last reviewed: 22 October 2026. The calculation is covered by automated tests with known answers taken from the sources above. Found an error? Please let us know.