A seasoned cord of firewood holds about 20 million Btu, and roughly 15.3 million Btu of that ends up as usable heat at the efficiency the US Forest Service uses. Divide your season’s heat need by that number to get cords. The tables below do it for typical heat needs and for the fuel you burned last winter.
Cords of seasoned firewood by heat needed
| Usable heat needed in a season | Full cords | Face cords (16 in pieces) |
|---|---|---|
| 10 million Btu | 0.7 | 2.0 |
| 25 million Btu | 1.6 | 4.9 |
| 50 million Btu | 3.3 | 9.8 |
| 75 million Btu | 4.9 | 14.7 |
| 100 million Btu | 6.5 | 19.6 |
| 125 million Btu | 8.2 | 24.5 |
| 150 million Btu | 9.8 | 29.4 |
Same heat as last winter’s fuel
| Fuel | Amount | Cords of seasoned firewood for the same usable heat |
|---|---|---|
| Heating oil (#2) | 100 gallons | 0.75 |
| Propane | 100 gallons | 0.47 |
| Natural gas | 100 therms | 0.52 |
| Electricity | 1,000 kWh | 0.22 |
| Premium wood pellets | 1 ton | 0.89 |
Calculator: from your fuel bills
How to read these numbers
- Typical use. FPL says that between 50 and 150 million Btu of energy are typically used to heat an average-sized home over a heating season, which is about 3 to 10 cords of seasoned wood if wood is the only heat.
- Efficiencies are typical values. FPL’s figures were developed with commercial boilers in mind, not residential units. A stove or furnace that is less efficient than 77% needs more wood; check your appliance’s rating.
- Species matters. A cord of dense oak or hickory holds much more heat than a cord of pine or aspen; see the firewood BTU chart by species.
- Dry wood only. FPL’s figure is for seasoned wood (20% moisture content). EPA says wood burns best below 20% moisture and recommends seasoning for at least six months.
- Burn only dry, split, well-seasoned wood, and test it with a wood moisture meter before you burn it (EPA).
- Store wood outdoors, off the ground, with only the top covered (EPA).
- Never burn coated, painted or pressure-treated wood, plywood or particle board, household trash or plastics (EPA).
- Have a professional inspect fireplaces, wood stoves, chimneys, flues and vents each year (CPSC).
- Fuel-burning heating, fireplaces included, can produce carbon monoxide: put CO alarms on every level of the home and outside sleeping areas (CPSC).
Buying wood? See cord, face cord and rick sizes. To compare wood with other fuels, see the heating fuel BTU chart.
Frequently asked questions
How much firewood do I need for a winter?
If wood is your only heat, FPL’s typical range of 50 to 150 million Btu a season works out to about 3 to 10 cords of seasoned wood. Supplemental use in one room needs far less.
How many BTU are in a cord of firewood?
About 20 million Btu gross for seasoned wood (FPL; EIA also uses 20 million Btu per cord), or about 15.3 million Btu of usable heat at 77% efficiency. Dense hardwoods hold more and softwoods less.
How long should firewood season?
EPA recommends at least six months, and says wood burns best at a moisture content of less than 20 percent.
Sources
- USDA Forest Service, Forest Products Laboratory. Techline WOE-3, “Fuel Value Calculator” (updated January 2024): gross and net heating values and efficiencies. A US Government work, available from the Forest Products Laboratory, Madison, Wisconsin.
- US Energy Information Administration. “British thermal units (Btu)”, Energy Explained (sample Btu conversion factors), eia.gov, read 12 November 2026.
- US Environmental Protection Agency, Burn Wise. “Best Wood-Burning Practices”, epa.gov, read 12 November 2026.
- US Consumer Product Safety Commission. “Keep Warm and Safe This Winter: Tips for Using Generators, Furnaces and Space Heaters”, news release, 23 January 2026, cpsc.gov.
Last reviewed: 12 November 2026. Numbers in the tables are our arithmetic from the sources listed. How we check our work: methodology and corrections. Spotted an error? Please let us know.