How to use this calculator
Select a wood species from the dropdown to see its BTU rating and burning characteristics. Enter the number of cords you plan to burn (decimals like 0.5 are fine for partial cords). Optionally enter a price per cord to see cost per million BTU and a full cost efficiency ranking across all wood types.
Set your heating season length in months so the calculator can show monthly BTU output. The equivalent heating section shows how many therms of natural gas or gallons of propane your firewood supply would replace, along with approximate dollar equivalents.
Understanding firewood BTU values
BTU per cord varies dramatically between species. Dense hardwoods like Osage orange and hickory pack 28 to 33 million BTUs into a single cord, while lightweight softwoods like cedar and spruce deliver only 13 to 16 million BTUs. This means you may need nearly twice as much softwood to produce the same heat as a quality hardwood.
Keep in mind that published BTU values assume properly seasoned wood at around 20% moisture content. Burning green or partially seasoned wood can reduce actual heat output by 25% to 50% because so much energy goes toward evaporating moisture.
Frequently asked questions
What are BTU ratings for firewood and why do they matter?
BTU stands for British Thermal Unit. It measures the heat energy released when wood burns. Higher BTU per cord means more heat from less wood, which saves money, storage space, and effort hauling and stacking.
How long should firewood be seasoned before burning?
Most species need 6 to 12 months of seasoning after splitting. Dense woods like oak benefit from a full year or more. The goal is to reach below 20% moisture content for clean, efficient burning.
How do I calculate cost per million BTU for firewood?
Divide the price per cord by the number of million BTUs that species produces. For example, white oak at $250 per cord with 29.1 million BTUs gives you about $8.59 per million BTU. This makes it easy to compare against natural gas or propane.
How much wood is in a cord and how is it measured?
A full cord measures 4 feet by 4 feet by 8 feet (128 cubic feet) when neatly stacked. A face cord is one row deep (usually 16 inches) at the same height and length, roughly one third of a full cord. Always clarify which measurement a seller is using.