Firewood Calculator
A firewood calculator divides seasonal heat need (sq ft × BTU per sq ft) by about 20 million BTU per cord. 2,000 sq ft at 15,000 BTU/sq ft needs 1.5 cords.
How much firewood you need for a season
A firewood calculator turns your home’s heating need into cords of wood. Multiply the heated floor area by the heat it uses per square foot over a winter. Then divide by the heat in one cord of seasoned hardwood, about 20 million BTU. Cords = (area × BTU per sq ft per season) ÷ 20,000,000. A 2,000 sq ft home at 15,000 BTU per sq ft needs 30 million BTU, or 1.5 cords.
The answer is a planning figure for a home heated entirely by wood. If wood is a supplement, scale it down by the share of heat it supplies.
The two inputs explained
- Home area to heat. Only the space the stove warms. A wood stove in a closed-off living room may heat 800 sq ft, not the whole house.
- Season BTU per sq ft. This bundles your climate, insulation, and air leakage into one number. The default of 15,000 suits a tight, well-insulated house in a mild winter. Older houses in cold regions often run two or three times higher.
The calculator divides by 20 million BTU per cord. That is a common planning figure for seasoned dense hardwood.
Worked examples
- Default: 2,000 sq ft at 15,000 BTU per sq ft
- Heat needed: 2,000 × 15,000 = 30,000,000 BTU
- Cords: 30,000,000 ÷ 20,000,000 = 1.50 cords
- Calibrating from last winter’s oil bill: 1,800 sq ft, 600 gallons of oil
- Heat delivered: 600 × 138,500 BTU × 0.80 furnace efficiency ≈ 66,480,000 BTU
- Per square foot: 66,480,000 ÷ 1,800 ≈ 36,900 BTU per sq ft
- Enter 1,800 and 36,900: 1,800 × 36,900 ÷ 20,000,000 = 3.32 cords
- With a stove at 70% efficiency: 3.32 ÷ 0.70 ≈ 4.7 cords
Example 2 shows why your own bills beat a guessed factor. The same calculator gives 1.5 cords or nearly 5, depending on the house.
Relative heat value of common firewood
| Wood | Heat per cord compared with oak |
|---|---|
| Hickory | a little more |
| Oak (red or white) | baseline |
| Sugar maple, beech | about the same |
| Ash | slightly less |
| Birch, cherry | noticeably less |
| Pine, spruce, fir | roughly a quarter to a third less |
| Aspen, cottonwood, willow | about a third less |
Published BTU-per-cord figures vary between sources. Use this as a ranking, and order more if your wood is mostly lighter species.
How a cord is measured
| Unit | Stack size | Volume |
|---|---|---|
| Full cord | 4 × 4 × 8 ft | 128 ft³ |
| Face cord (16 in logs) | 4 ft high × 8 ft long × 16 in deep | about 43 ft³, one-third of a cord |
| Half cord | 4 × 4 × 4 ft | 64 ft³ |
Sellers use “face cord,” “rick,” and “truckload” differently. Ask for the stack dimensions and check them with the cord of wood calculator.
Common mistakes
- Burning green wood. Freshly cut wood holds a lot of water. Much of its heat goes into boiling that water off. Season split wood for six months to a year or more.
- Buying face cords as full cords. A face cord of 16-inch logs is a third of a full cord.
- Ignoring stove efficiency. The calculator assumes all of the wood’s heat reaches the room.
- Heating the whole house area with a single stove. Enter only the area the stove really reaches.
Related calculators
To see how much heat your house loses, use the heat loss calculator. The BTU calculator sizes heating for a single room, and the furnace size calculator compares the job against a central system.
A rough seasonal planning estimate. Actual firewood use depends on climate, insulation, wood species, moisture, stove efficiency, and how much of your heat comes from wood.
Frequently asked questions
How many cords of firewood do I need for winter?
Multiply your heated area by a seasonal BTU-per-square-foot figure, then divide by about 20 million BTU per cord of seasoned hardwood. A 2,000 sq ft home at 15,000 BTU per sq ft needs 30 million BTU, or 1.5 cords. Cold, drafty houses can need several times that.
Where does the BTU-per-square-foot figure come from?
It is the total heat your house uses over a season, divided by its area. The best way to find it is from past fuel bills: heating oil holds about 138,500 BTU per gallon, so 600 gallons burned at 80% efficiency is about 66.5 million BTU; over 1,800 sq ft that is about 36,900 BTU per sq ft.
Why is a cord measured in BTUs?
Because heat is what you are buying. A full cord is a stack 4 × 4 × 8 ft, or 128 cubic feet, and a cord of seasoned dense hardwood is commonly figured at around 20 million BTU of heat content. Dividing your season's heat need by that figure turns energy into a stack you can order.
Does wood species change how many cords I need?
Yes. Dense hardwoods such as oak, hickory, and sugar maple hold more heat per cord than light woods such as pine, aspen, or cottonwood, which can hold roughly a quarter to a third less. Burning mostly softwood means ordering more cords.
Does my stove's efficiency matter?
Yes. The 20 million BTU figure is the heat in the wood, not the heat delivered to the room. Divide the result by your stove's efficiency: at 70%, 1.5 cords becomes about 2.1 cords. Open fireplaces send most of the heat up the chimney and need far more.
Estimates only. Verify quantities with your supplier before purchasing.