How it works
Heat comes from the dry wood substance, so denser species pack more energy into the same cord. The calculator starts from each species' published density (specific gravity), estimates how much dry wood a stacked cord holds, and multiplies by the heating value of dry wood.
Water then costs energy. Every pound of moisture in the wood takes about 1,100 BTU to boil off and carry up the flue, so wet wood delivers far less useful heat than the same wood seasoned. Your stove or furnace efficiency sets how much of what remains reaches the room.
Worked example
One cord of white oak at 20% moisture burned in a 70% efficient stove:
- Dry wood per cord = 0.6 SG × 62.4 lb/ft³ × 128 ft³ × 0.75 = 3,594 lb
- Water = 3,594 lb × 20% ÷ (1 − 20%) = 899 lb
- Usable heat = 3,594 × 8,200 − 899 × 1,100 = 28,484,352 BTU per cord
- = 28.5 million BTU per cord
- Delivered = 28.5 × 1 cords × 70% = 19.9 million BTU (144 gal of fuel oil)
| Input | Value |
|---|---|
| Species | White oak |
| Moisture content (wet basis) | 20 % |
| Cords of wood | 1 cords |
| Stove or furnace efficiency | 70 % |
| Result | Value |
|---|---|
| Dry wood mass per cord | 3,594 lb |
| Usable heat in wood, per cord | 28.5 million BTU |
| Delivered heat, all cords | 19.9 million BTU |
| Delivered heat equals about | 144 gal of #2 fuel oil |
Heat by species
| Species | Specific gravity | Dry wood per cord (lb) | Usable heat at 20% moisture (million BTU per cord) |
|---|---|---|---|
| White oak | 0.6 | 3594 | 28.5 |
| Northern red oak | 0.56 | 3355 | 26.6 |
| Bur oak | 0.58 | 3474 | 27.5 |
| Sugar (hard) maple | 0.56 | 3355 | 26.6 |
| Red maple | 0.49 | 2935 | 23.3 |
| Silver maple | 0.44 | 2636 | 20.9 |
| White ash | 0.55 | 3295 | 26.1 |
| Green ash | 0.53 | 3175 | 25.2 |
| Yellow birch | 0.55 | 3295 | 26.1 |
| Paper birch | 0.48 | 2875 | 22.8 |
| Black walnut | 0.51 | 3055 | 24.2 |
| Black cherry | 0.47 | 2815 | 22.3 |
| American elm | 0.46 | 2756 | 21.8 |
| Hackberry | 0.49 | 2935 | 23.3 |
| Shagbark hickory | 0.64 | 3834 | 30.4 |
| Black locust | 0.66 | 3954 | 31.3 |
| Quaking aspen | 0.35 | 2097 | 16.6 |
| American basswood | 0.32 | 1917 | 15.2 |
| Eastern cottonwood | 0.37 | 2216 | 17.6 |
| Yellow-poplar | 0.4 | 2396 | 19 |
| Eastern white pine | 0.34 | 2037 | 16.1 |
| Red pine | 0.41 | 2456 | 19.5 |
| Tamarack | 0.49 | 2935 | 23.3 |
| Douglas-fir (coast) | 0.45 | 2696 | 21.4 |
| Western redcedar | 0.31 | 1857 | 14.7 |
| Balsam fir | 0.33 | 1977 | 15.7 |
| White spruce | 0.33 | 1977 | 15.7 |
Show the heat by species table
| Species | Specific gravity | Dry wood per cord (lb) | Usable heat at 20% moisture (million BTU per cord) |
|---|---|---|---|
| White oak | 0.6 | 3594 | 28.5 |
| Northern red oak | 0.56 | 3355 | 26.6 |
| Bur oak | 0.58 | 3474 | 27.5 |
| Sugar (hard) maple | 0.56 | 3355 | 26.6 |
| Red maple | 0.49 | 2935 | 23.3 |
| Silver maple | 0.44 | 2636 | 20.9 |
| White ash | 0.55 | 3295 | 26.1 |
| Green ash | 0.53 | 3175 | 25.2 |
| Yellow birch | 0.55 | 3295 | 26.1 |
| Paper birch | 0.48 | 2875 | 22.8 |
| Black walnut | 0.51 | 3055 | 24.2 |
| Black cherry | 0.47 | 2815 | 22.3 |
| American elm | 0.46 | 2756 | 21.8 |
| Hackberry | 0.49 | 2935 | 23.3 |
| Shagbark hickory | 0.64 | 3834 | 30.4 |
| Black locust | 0.66 | 3954 | 31.3 |
| Quaking aspen | 0.35 | 2097 | 16.6 |
| American basswood | 0.32 | 1917 | 15.2 |
| Eastern cottonwood | 0.37 | 2216 | 17.6 |
| Yellow-poplar | 0.4 | 2396 | 19 |
| Eastern white pine | 0.34 | 2037 | 16.1 |
| Red pine | 0.41 | 2456 | 19.5 |
| Tamarack | 0.49 | 2935 | 23.3 |
| Douglas-fir (coast) | 0.45 | 2696 | 21.4 |
| Western redcedar | 0.31 | 1857 | 14.7 |
| Balsam fir | 0.33 | 1977 | 15.7 |
| White spruce | 0.33 | 1977 | 15.7 |
Specific gravity from USDA Wood Handbook Table 5-3a. Heat uses 8,200 BTU per dry pound and 1,100 BTU per pound of water, per stacked cord.
Assumptions and limits
- Specific gravity is basic specific gravity (oven-dry weight ÷ green volume) from the USDA Wood Handbook, Table 5-3a.
- A stacked cord is assumed to be 75% solid wood; loose, crooked, or very small splits are lower.
- Uses 8,200 BTU per dry pound as an average across species. Conifers run a little higher because of resin, so pine and spruce are slightly understated.
- Published cord charts vary by source by ±10%. Use this for comparing species and moisture, not as a precise fuel-supply figure.
Common questions
What is the best firewood for BTU?
Dense hardwoods lead: black locust, shagbark hickory, ironwood, and white oak. In northern Minnesota, sugar maple, white ash, and yellow birch are the practical high-heat choices.
How much does moisture matter?
Evaporating the water costs energy: in this model, going from 20% to 45% moisture costs about 8–10% of the heat in the wood. Real losses are larger, because wet wood also burns cooler, smokes, and builds creosote, which lowers stove efficiency further.
How many BTU is a cord of firewood?
Roughly 16 to 31 million BTU per stacked cord of seasoned wood, depending on species. Use the tool above for a specific species and moisture level.
How long does firewood take to season?
Split, stacked off the ground, and covered on top, most hardwoods need 12–24 months; oak often needs the full two years. Softwoods need 6–12 months.
Sources
- USDA Forest Products Laboratory, Wood Handbook: Wood as an Engineering Material (FPL-GTR-282, 2021): Table 5-3a (green specific gravity).
- Heating value of about 8,200 BTU per oven-dry pound and 1,100 BTU per pound of water evaporated are typical engineering values; published cord charts vary by source.
- Read them: USDA Wood Handbook, Chapter 5 (specific gravity)
Updated 2026-09-30