Firewood Moisture Meter: How to Test Wood and Read the Number
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A moisture meter tells you whether firewood is dry enough to burn well. The number to look for is below 20 percent. The U.S. Environmental Protection Agency's Burn Wise program says wood burns best below that level, and the U.S. Department of Energy also gives 20 percent or less, by weight, as the mark of good firewood. Anything above it still has water to lose.
Why 20 percent
Wet wood burns poorly because part of its heat goes into driving water out of the wood instead of heating your home. The heat values on the BTU chart assume dry wood. A cord that tests well above 20 percent will give you less usable heat than the chart says.
The calendar does not tell you the moisture level. How fast wood dries depends on the species, how it was split and stacked, and the weather. A meter reading does. That is why the seasoning guide treats the meter as the real test of whether wood is ready.
How to test a piece of firewood
- Pick a piece and split it in half. The outside of a log or split can be drier than the middle.
- Test the freshly split face. Use the newly exposed surface, not the bark side or an old cut end. Follow the instructions that came with your meter for how to take a reading.
- Test several pieces. One reading proves little. Take readings from pieces from different parts of the stack, such as the top, the middle and the bottom.
- Write the numbers down. Compare them to the 20 percent target.
How to read the number
| Reading | What it means |
|---|---|
| Under 20% | Ready to burn. |
| Above 20% | Not ready. It needs more drying time. |
If a piece reads above 20%, keep it stacked off the ground and test it again later with a freshly split face. Look at the wettest readings, not just the best ones. They tell you how much of the stack still needs time.
Example (made-up readings)
Say you test five pieces from different parts of a stack and get 15, 17, 18, 19 and 26 percent.
- Four of the five pieces are under 20 percent.
- The fifth, at 26 percent, is not ready.
- The stack is not uniformly dry. Burn the pieces that tested under 20 percent first and leave the wetter pieces to dry longer.
One reading of 15 percent would have hidden the 26 percent piece. This is why you test more than one.
When a reading can mislead you
- You tested the outside. The surface of a piece can dry faster than its middle, so an unsplit reading may look better than the wood really is. Split the piece and test the fresh face.
- You tested only one piece. Pieces in the same stack dry at different rates.
- You tested only the best-looking piece. Test pieces from several places, including the ones that look or feel heaviest.
Quick checklist
- Target: under 20 percent.
- Split first, then test the fresh face.
- Test several pieces from different parts of the stack.
- If a reading is above 20 percent, wait and test again.
Sources
- U.S. Environmental Protection Agency, Burn Wise (archived), Best Wood-Burning Practices and Test Your Wood with a Moisture Meter. EPA stopped updating the Burn Wise site on October 30, 2025; the guidance remains online as an archive.
- U.S. Department of Energy, Wood and Pellet Heating: 20% moisture or less by weight.