Firewood BTU Calculator

A full cord is 128 cubic feet of tightly stacked wood — the classic pile is 4 feet high, 4 feet deep, and 8 feet long. That measurement is of the stack as a whole, including the air gaps, so only about 80 percent is actually solid wood.

Because it is a volume, the same cord can be stacked many ways: 2 ft × 4 ft × 16 ft gives the same 128 cubic feet. Always measure a delivery stacked and square rather than loose in a truck bed.

A face cord, also called a rick, is a stack 4 feet high and 8 feet long but only one log deep — so its volume depends entirely on how long the logs are cut. A full cord is always 128 cubic feet.

At a common 16-inch log length, three face cords make one full cord. At 12 inches it takes four, and at 24 inches only two. That is why face cord is a loose term to watch when buying — always ask for the log length before comparing prices.

It depends heavily on the species. A cord of dense hardwood like oak, hickory, or black locust holds roughly 24 to 28 million BTU, while a cord of softwood like pine or aspen holds closer to 12 to 17 million BTU.

Those are gross figures for seasoned wood. What actually reaches your room is lower, because both the moisture in the wood and your appliance’s efficiency take a cut before the heat is delivered.

The densest hardwoods top the list. Osage orange (hedge) leads at around 33 million BTU per cord, followed by shagbark hickory, black locust, and white oak in the high-20s, with sugar maple, beech, and red oak in the mid-20s.

Heavier wood holds more energy per cord, which is why hardwoods are prized for long, overnight burns. Softwoods light easily and are fine for shoulder-season fires, but you will burn through more of them for the same heat.

Yes, a great deal. Freshly cut green wood can be over 45 percent water, and boiling off that water steals energy that would otherwise heat your room — cutting usable output by roughly a quarter.

Properly seasoned wood sits under 20 percent moisture, lights easily, burns hotter, and produces far less creosote. Most hardwoods need six to twelve months split and stacked before they are ready to burn well.

A rough rule is two to five full cords to heat an average home for a season, depending on climate, house size, insulation, and how much of the load the wood carries versus a backup system.

The calculator turns this around: enter your stack and a daily heat need, and it estimates how many heating days your wood will cover. A home in a cold climate often needs 400,000 to 600,000 BTU of delivered heat on a winter day.

A cord of seasoned hardwood delivers heat roughly on par with 140 to 200 gallons of heating oil or 180 to 210 therms of natural gas, once furnace and stove efficiencies are accounted for. The calculator shows the exact equivalents for your own wood.

Whether wood is cheaper depends entirely on local prices. The cost-per-million-BTU figure lets you compare your firewood price directly against your utility rates on the same footing.

Two losses stand between the wood and your room. First, any moisture has to be boiled off before the wood can burn hot. Second, no appliance is perfectly efficient — an open fireplace may deliver only about 10% of the wood’s energy, an older stove around 50%, and a modern EPA-certified stove 70–80%.

The rest goes up the chimney as heat and unburned gases. That is why a smaller load in an efficient stove can out-heat a roaring open fire.