How it works
Wood is hygroscopic: it gains or loses water until it matches the humidity of the surrounding air. That balance point is the equilibrium moisture content, or EMC. It depends mostly on relative humidity and only slightly on temperature.
The Wood Handbook publishes EMC for temperatures from 30 to 210°F and relative humidities from 5 to 95%. This tool reads that table and interpolates between its points. Use it to see what moisture content your shop or home will push wood toward, and how far it swings between winter heat and summer humidity.
Worked example
A shop at 70°F that runs 30% relative humidity in winter and 65% in summer, aiming for 8% wood moisture content:
- Wood Handbook Table 4-2 at 70°F and 30% RH (interpolated) = 6.2% MC
- Table 4-2 at 70°F and 65% RH = 12% MC
- Seasonal swing = 12 − 6.2 = 5.8 points of moisture content
- A 8% target needs about 42% RH at 70°F
| Input | Value |
|---|---|
| Air temperature | 70 °F |
| Relative humidity, dry season (winter heat) | 30 % |
| Relative humidity, humid season (summer) | 65 % |
| Target wood moisture content | 8 % |
| Result | Value |
|---|---|
| Wood moisture content, dry season | 6.2 % |
| Wood moisture content, humid season | 12 % |
| Seasonal swing | 5.8 points of MC |
| Relative humidity that holds the target moisture content | 42 % |
Equilibrium moisture content table
| Relative humidity (%) | At 50°F (%) | At 70°F (%) | At 90°F (%) |
|---|---|---|---|
| 10 | 2.6 | 2.5 | 2.3 |
| 20 | 4.6 | 4.5 | 4.3 |
| 30 | 6.3 | 6.2 | 5.9 |
| 40 | 7.9 | 7.7 | 7.4 |
| 50 | 9.5 | 9.2 | 8.9 |
| 60 | 11.2 | 11 | 10.5 |
| 70 | 13.4 | 13.1 | 12.6 |
| 80 | 16.4 | 16 | 15.4 |
| 90 | 20.9 | 20.5 | 19.8 |
Show the equilibrium moisture content table table
| Relative humidity (%) | At 50°F (%) | At 70°F (%) | At 90°F (%) |
|---|---|---|---|
| 10 | 2.6 | 2.5 | 2.3 |
| 20 | 4.6 | 4.5 | 4.3 |
| 30 | 6.3 | 6.2 | 5.9 |
| 40 | 7.9 | 7.7 | 7.4 |
| 50 | 9.5 | 9.2 | 8.9 |
| 60 | 11.2 | 11 | 10.5 |
| 70 | 13.4 | 13.1 | 12.6 |
| 80 | 16.4 | 16 | 15.4 |
| 90 | 20.9 | 20.5 | 19.8 |
Excerpt of USDA Wood Handbook Table 4-2, which lists 30 to 210°F in 10-degree steps and 5 to 95% humidity in 5-point steps.
Assumptions and limits
- Moisture content is measured on an oven-dry basis, the way moisture meters read it.
- Values are for clear wood of all species combined. Species with more extractives, such as some tropical woods and cedar, sit lower at high humidity.
- Wood in a room takes days to months to reach equilibrium, depending on thickness and finish.
- A moisture meter reads a board directly. Use this table to understand what to expect, not to replace a meter reading.
Common questions
What is the equilibrium moisture content of wood indoors?
It depends on your room's humidity. At 70°F the Wood Handbook table gives 6.2% at 30% relative humidity, 9.2% at 50%, and 12.0% at 65%.
What moisture content should furniture lumber be?
Match it to where it will live: the average EMC of that room across the seasons. Log the room's humidity with a hygrometer and read the average moisture content off this calculator.
Does temperature change the EMC much?
Only a little. Going from 70°F to 100°F at 50% humidity lowers EMC from 9.2% to 8.7%. Relative humidity is the big factor.
How do I measure relative humidity?
Use a hygrometer in the room where the wood will be stored or used, and log it over a season. Weather-station humidity is outdoors and can differ a lot from your shop.
Sources
- USDA Forest Products Laboratory, Wood Handbook: Wood as an Engineering Material (FPL-GTR-282, 2021), Chapter 4, Table 4-2: Moisture content of wood in equilibrium with stated temperature and relative humidity.
- Read them: USDA Wood Handbook, Chapter 4 (Table 4-2)
Updated 2026-09-30