Calculator
Moisture content and acclimation guide
Pick your state to see the moisture content the USDA Wood Handbook recommends for indoor woodwork, flooring and furniture. Then check what your shop air will dry wood to.
Target moisture content for your area
JavaScript is off, so the picker and calculator cannot run. Use the table below: most of the US is 8% (6–10%), the dry Southwest is 6% (4–9%), and the damp, warm coast is 11% (8–13%).
Interior use: woodwork, flooring, furniture and trim. From Wood Handbook Table 13–2 and Figure 13–1.
Equilibrium moisture content (EMC)
Wood kept long enough in steady air ends up at a moisture content set by the temperature and relative humidity. Enter your shop or room conditions.
Wood will settle at about —
Enter a temperature from 30 to 200 °F and a humidity from 0 to 98%.
This is an average for typical wood. Real wood can differ by species and by whether it is drying or taking on moisture.
Wood Handbook recommended moisture content, interior use
| Area | Average | Single pieces |
|---|---|---|
| Most of the US | 8% | 6–10% |
| Dry Southwest | 6% | 4–9% |
| Damp, warm coastal area | 11% | 8–13% |
Acclimating wood
- Bring the wood into the room where it will live, or into conditions like it, and let it sit with air around every board.
- For flooring, open the bundles so all sides are exposed to the air inside the house, and run the heating system before the flooring arrives.
- Check random pieces with a moisture meter when the wood arrives and again before you install or build.
- Keep checking until the readings stop changing. The Wood Handbook says that if the average is within 1% of the recommended value and every piece is inside the range, the lot is probably fine.
- There is no set number of days. Thick stock, wet wood and damp weather all take longer.
About moisture meters
- Meters vary by species setting. Set the meter to your species, or apply the species correction that came with it.
- Pin (resistance) meters read lower than true in cold wood and higher in warm wood. Follow the maker’s temperature correction.
- Pinless meters read mostly the surface, so a wet core may not show.
How much will the board move?
To see how much a board shrinks or swells when its moisture content changes, use the wood movement calculator.
The math
The calculator uses Wood Handbook Equation 4–5: EMC = (1,800 ÷ W) × [Kh ÷ (1 − Kh) + (K₁Kh + 2K₁K₂K²h²) ÷ (1 + K₁Kh + K₁K₂K²h²)], where h is relative humidity as a decimal and, for T in °F, 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.
Worked example
At 70 °F and 50% relative humidity, W = 381.98, K = 0.8193, K₁ = 5.936 and K₂ = 2.635, so Kh = 0.4096. The equation gives about 9.2%, the same as the Wood Handbook table. That is a little above the 8% average for most of the US.
Sources
The moisture targets, the 1% rule and the EMC formula come from the USDA Forest Products Laboratory Wood Handbook (2021). Which zone each state falls in is our reading of the Handbook's map, which doesn't list states.
- Wood Handbook FPL-GTR-282, ch. 13, Table 13–2 and Figure 13–1, p. 13–5 (recommended moisture content, interior use); p. 13–3 (within 1% of recommended); pp. 13–2 to 13–3 (meter species and temperature corrections); p. 13–19 (flooring practices) (external site, opens in a new tab)
- Wood Handbook FPL-GTR-282, ch. 4, Equation 4–5, p. 4–3, and Table 4–2, p. 4–4 (equilibrium moisture content) (external site, opens in a new tab)
This guide gives general targets for planning. Indoor conditions vary with heating, air conditioning, basements and crawl spaces, so measure your own wood and room. Flooring and product makers may set their own moisture requirements; follow them.
This calculator runs in your browser only. Your choices aren't sent to us or anyone else, and the calculator doesn't save them or use your location. The page itself uses analytics; see our privacy policy.
Related on this site
We pick tools from independent tests and reviews, not our own testing.