Firewood Consumption Calculator

How much firewood do I need for one winter?

Between three and six cords for most American homes heated mainly with wood — but that range is wide enough to be useless if you are the one buying. Four things set the real number:

• How much heat the house loses. Floor area is a poor proxy for this, which is why the first method here skips it entirely and reads the answer off your fuel bill instead.
• The climate. Measured in heating degree days, not in latitude or in feel.
• The species. A cord of live oak holds nearly three times the heat of a cord of northern white-cedar.
• The stove. Half the energy in the wood can go up the chimney, or a fifth of it, depending on the appliance and how it is run.

Miss any one of the four and the answer can be out by a factor of two. Most online calculators ask for floor area alone.

How do I turn my propane or oil bill into cords?

This is the most reliable way, and it takes one number you already have. Last year's fuel already reflects your house, your habits and your winter. What remains assumed is the efficiency of the old appliance and of the stove, so the result is an estimate, but a much better-grounded one than floor area alone.

The arithmetic runs in three steps:

1. Fuel into energy. Multiply the quantity by its heat content. The federal figures are 91,452 Btu per gallon of propane, 138,500 per gallon of No. 2 heating oil, 100,000 per therm of natural gas (1,036 per cubic foot), and 3,412 per kilowatt-hour.
2. Energy into heat that reached the rooms. Multiply by the efficiency of the system that burned it. A furnace rated 80 % AFUE sent a fifth of it up the flue.
3. Heat into wood. Divide by the heat in a cord of the species you will burn, times your stove's efficiency.

Worked through: 800 gallons of propane in an 80 % furnace delivered 58.5 million Btu into the house. A cord of northern red oak holds 23.7 million, of which a 50 % stove delivers 11.8. That is 4.9 cords to replace the propane entirely.

Why does the same house need three times more wood in Minnesota than in Alabama?

Because heating demand tracks heating degree days almost exactly, and the spread between states is enormous. A degree day counts how far the daily average temperature falls below 65 °F, added up over the year — it is the closest thing there is to a single number for “how hard is winter here”.

Population-weighted means the figure describes where people in the state actually live rather than its emptiest corner — the average Californian is not on Mount Whitney. All 51 entries, plus the District of Columbia, are in the calculator.

Which species gives the most heat per cord?

Density decides it. Heat per pound of ovendry wood barely varies between species — about 8,600 Btu whatever the tree — so a cord's heat is set almost entirely by how much wood mass fits into the 128 cubic feet. Dense hardwoods win, and light softwoods lose, in direct proportion.

That also means you can compute it for any species from its specific gravity rather than hunting for it in a published table. Every figure on this page is computed that way, which is why softwoods that the usual tables ignore are covered too. The Firewood BTU Chart ranks all 146 species, heat in the wood and heat delivered, and shows what burning them green costs.

Why is “one cord = 20 million Btu” wrong?

Because there is no such thing as a generic cord. The US Energy Information Administration does publish that single figure, and it is a reasonable national average for statistics — but applied to the wood in your own shed it is badly wrong at both ends.

Across the 146 species in the USDA dataset, a cord runs from 11.6 million Btu (northern white-cedar) to 33.1 million (live oak). Against those, the flat figure overstates the cedar by 72 % and understates the live oak by 40 %. Buy on the flat figure and you can end the winter two cords short.

How efficient is my wood stove, really?

Lower than the brochure says, and the gap is systematic rather than accidental. The EPA warns that advertisements normally quote combustion efficiency, the higher of the two numbers, and that the overall efficiency — the share that actually reaches the room — runs 10 to 20 points below it. A stove advertised at 85 % may deliver 65 %.

The EPA publishes no default value to fill the gap, and says as much: the figure for a specific stove comes from its certification. Any stove built after 1 May 2015 has one on file. An open masonry fireplace is a separate case — most of its heat leaves by the chimney, and it can pull more warm air out of a house than it puts in.

How much space will that wood take up?

A cord is 128 cubic feet stacked, so the wall of wood is easy to picture once the piece length is fixed. Stacked four feet high in 16-inch pieces, one cord is 24 feet long. Five cords is 120 feet — which surprises most people planning their first season, and is worth checking against the space you actually have before the delivery arrives.

Longer pieces make a shorter stack for the same volume: at 24 inches, a cord needs only 16 feet of wall. The calculator follows the piece length you enter.

Weight is the other surprise: a seasoned cord of hardwood is about 3,000 to 3,400 lb, so a winter's supply is several tons to move. The Cord of Wood Weight Calculator gives the weight by species and the number of trips your vehicle needs.

Frequently asked questions

Is a face cord enough for a winter? Almost certainly not, and it is not a legal unit of sale in the first place. A “face cord” of 16-inch pieces is a third of a cord, so three of them make one. If a seller quotes you face cords, the Face Cord Calculator converts the quote into full cords, and how firewood must legally be sold explains why the term is banned.

Should I buy green wood and season it myself? It is cheaper per cord and it works, provided you buy a year ahead. Wood burned before it has dried gives up a large share of its energy evaporating its own water, so a cord of green wood delivers noticeably less heat than the figures here — which assume seasoned wood throughout.

Does a heat pump change the calculation? Yes, and this tool deliberately leaves heat pumps out. They move heat rather than make it, so they deliver two to four times the energy they consume, and expressing that as an efficiency percentage alongside a furnace would be misleading.

My house is bigger than average. Can I just scale the answer? On the house method, yes — the estimate is linear in floor area. But a bigger house is not reliably a proportionally leakier one, which is why the fuel-bill method is the better road whenever you have a bill.

Why does the calculator ask what share wood will cover? Because most people who heat with wood do not heat only with wood. Covering half the load needs half the wood, and the saving should be compared against half the fuel bill, not all of it.

Sources

• U.S. Energy Information Administration, British thermal units (Btu) — heat content per unit of fuel.
• U.S. EIA, State Energy Data System, Population, GDP, and degree days — heating degree days by state, 1960–2024.
• U.S. EIA, Residential Energy Consumption Survey 2020, Table CE3.1, annual household site end-use consumption — released June 2023, revised March 2024.
• U.S. EIA, RECS 2020, Table HC10.1, total square footage of U.S. homes — released March 2023.
• U.S. Department of Energy, FEMP, Purchasing Energy-Efficient Residential Furnaces — AFUE reference levels, updated December 2024.
• U.S. EPA Burn Wise, Energy Efficiency and Your Wood-Burning Appliance — overall versus combustion efficiency.
• Miles, P.D.; Smith, W.B. 2009. Specific Gravity and Other Properties of Wood and Bark for 156 Tree Species Found in North America. USDA Forest Service, Research Note NRS-38.
• University of Arkansas Extension, FSA-1091, Basics of Heating with Firewood — 8,600 Btu per ovendry pound, 50 % burning efficiency.