Firewood Heat Calculator
Cord heat in BTU, kWh, and propane gallons.
What it does
Firewood sells by volume but heats by density and dryness. A cord is a fixed stack of 128 cubic feet, yet the solid wood inside and the water inside vary widely. Dense seasoned oak near 25 million BTU per cord holds almost twice the heat of cottonwood near 14.
The tool above turns cords and species into three comparable numbers. Two cords of oak give 50 million BTU, or 14,654 kWh, near 500 gal of propane. The metric mirror at 7.2 cubic meters gives 49.7 million BTU with 1,880 L of propane. Dividing the seller price by million BTU ranks offers fairly across species.
Moisture decides how much of that gross heat reaches the room. Green wood can hold half its weight as water, and each pound of water steals over a thousand BTU to boil off before the wood burns. Seasoned wood under about 20% moisture, plus a modern stove, delivers far more useful heat than the same species green.
This page reports gross heat in the wood. It does not subtract stove losses, chimney losses, or moisture penalties. Use it to compare fuels and piles, then discount for your stove and wood condition.
How to use
- Pick imperial (cords) or metric (cubic meters).
- Enter the stacked amount.
- Pick the species closest to your pile.
- Read million BTU first, then kWh.
- Read the propane equivalent for cost comparison.
- Divide price by heat to find the best buy per million BTU.
Formula
- cords
- Stacked cords, 128 cubic feet each. Metric converts by 3.6246 cubic meters per cord.
- species
- Seasoned heat per cord: oak 25, maple 24, ash 20, pine 15, cottonwood 14.
- propane
- Propane at near 100,000 BTU per gallon for comparison.
Species values are per seasoned cord: oak 25, maple 24, ash 20, pine 15, cottonwood 14. At zero cords there is no heat. Moisture, stove efficiency, and stacking air space sit outside this gross heat.
Worked example
Example: 2 cords of oak
Defaults: imperial 2 cords of oak. Metric mirror is 7.2 cubic meters. One cord is 128 cubic feet stacked.
- Inputs (imperial default): 2 cords of oak at 25 per cord.
- Heat: 2 times 25 is 50 million BTU.
- Electric: 50 times 293.071 is 14,654 kWh.
- Propane: 50 times 10 is 500 gal propane.
- Metric mirror (7.2 cubic meters oak) gives 49.7 million BTU, 14,554 kWh, 1,880 L propane. Tool shows the same.
Reference table
| Species | Per cord | 2 cords |
|---|---|---|
| Oak | 25 | 50 |
| Maple | 24 | 48 |
| Ash | 20 | 40 |
| Pine | 15 | 30 |
| Cottonwood | 14 | 28 |
Limits
- Gross heat only. Stove efficiency excluded.
- Seasoned values. Green wood gives far less.
- Stacked cords assumed. Loose piles hold more air.
- Species averages. Local wood varies with soil and cut.
Common mistakes
- Buying by pickup load instead of stacked cords.
- Comparing species by price per cord instead of per BTU.
- Burning green wood and blaming the stove.
- Ignoring moisture meter readings above 20%.
- Forgetting chimney and stove losses in heating plans.
Try it yourself
Quick checks. Answers sit tucked under each question.
1 cord of ash?
Heat is 1 times 20 is 20 million BTU. Electric is 5,861 kWh. Propane is 200 gal.
3 cords of cottonwood?
Heat is 3 times 14 is 42 million BTU. Electric is 12,309 kWh. Propane is 420 gal.
Questions
How is firewood heat figured?
Cords times species value. Here 2 times 25 is 50 million BTU.
How do BTU become kWh?
One million BTU is 293.071 kWh. Here 50 times 293.071 is 14,654 kWh.
How much propane equals a cord pile?
About 10 gal of propane per million BTU, since a gallon holds near 100,000 BTU. Here 50 times 10 is 500 gal.
Does species matter much?
Yes, a lot. Dry dense hardwoods lead; wet or light woods trail. Oak near 25 beats cottonwood near 14 per cord.
What is a cord?
A stacked cord is 128 cubic feet, often 4 by 4 by 8 ft. Solid wood inside is nearer 70 to 80 cubic feet.
Can I use green wood figures?
No. Wet wood spends heat boiling water and smokes. Burn seasoned wood under about 20% moisture.