Firewood Moisture Content Calculator
Enter your firewood moisture meter reading and this firewood moisture content calculator estimates how much usable heat is left in each cord — effective BTU, your percentage heat loss, and whether the wood is ready to burn or needs more seasoning.
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Enter a moisture reading to see effective heat, heat loss, and burn readiness.
How to use this calculator
Grab an inexpensive pin-type moisture meter, split a log open, and press the pins into the freshly exposed inner face — not the bark or the weathered ends. Enter that percentage, pick hardwood or softwood, and add how many cords you have.
The results show your effective heat per cord in million BTU, the total for all your cords, what share of the wood's potential heat is lost to moisture, and a readiness rating telling you whether to burn it now or keep seasoning it.
Seasoning tip: split logs season fastest. Stack them off the ground with airflow between rows, cover only the top, and give the stack 6–12 months (up to 2 years for dense oak) before burning.
How it works
This is a simplified estimate model, not a lab measurement. Bone-dry firewood holds roughly 25.0 MMBTU per cord for typical hardwoods and about 17.0 MMBTU per cord for typical softwoods — these are species-average figures, and real values vary by species and how tight the cord is stacked.
Wet wood delivers less heat because energy is wasted evaporating water before the wood can burn, and because wet wood burns cooler and less completely. The model captures this with a penalty factor:
Effective heat = gross heat × (1 − 0.85 × moisture content), where moisture content is a decimal (25% = 0.25), read wet-basis on a pin meter. The 0.85 factor approximates the latent heat lost boiling off the water plus the efficiency loss from cooler combustion. Heat loss % is simply (1 − effective ÷ gross) × 100.
Example: hardwood at 25% moisture gives 25.0 × (1 − 0.85 × 0.25) = 19.7 MMBTU per cord — about 21.3% of the heat is lost. This model does not estimate cord volume; it only prices the moisture penalty on a cord's heat content.
Frequently asked questions
What moisture content is best for firewood?
Firewood burns best at 15 to 20 percent moisture content (wet basis, as read by a pin meter). Below 15 percent it burns hot and clean, 15 to 20 percent is considered ready to burn, and anything over 25 percent should be seasoned longer before use.
How does moisture reduce the heat from firewood?
Wet wood wastes energy boiling off its water before it can actually burn, and it burns cooler and less completely. This calculator uses a simplified estimate: effective heat equals the bone-dry heat content multiplied by (1 minus 0.85 times the moisture content as a decimal). At 25 percent moisture, roughly a fifth of a cord's potential heat is lost.
How do I measure firewood moisture with a meter?
Use an inexpensive pin-type moisture meter. Split a log open first and press the pins into the freshly exposed inner face, not the bark or the dry-looking outer end, since that gives the truest reading of the wood's interior. Take a few readings across several splits and average them.
How long does firewood take to season?
Typically 6 to 12 months: split the logs, stack them off the ground with airflow between rows, and cover only the top so rain stays off but moisture can escape. Dense hardwoods like oak can take up to 2 years to drop below 20 percent moisture.