Firewood Calculator: How Many Cords Do You Need for Winter?

What Is a Cord of Firewood?

A full cord is the only legally defined unit for firewood in most U.S. states: a stack 4 ft × 4 ft × 8 ft = 128 cubic feet of space. Because logs aren't solid — there's air between pieces — the actual wood volume is roughly 80–90 cubic feet per cord, with 38–40 cubic feet of air.

Common terms that mean less than a cord:

A pickup truck load sold as "a cord" is almost always a face cord at most. Always buy by the full cord if you're heating primarily with wood.

How Much Firewood to Heat a Home

Heating needs vary enormously by climate, home insulation, stove efficiency, and how much of your heat comes from wood.

General estimates for a primary wood-heating home:

"Cold climate" = 5,000–8,000 heating degree days per year (northern states, New England, Upper Midwest). "Mild climate" = under 3,000 heating degree days (mid-Atlantic, Pacific NW coastal).

BTU Content by Wood Species

Not all firewood is equal. Hardwoods contain significantly more BTU per cord than softwoods.

Softwoods (pine, spruce, fir) burn faster and produce more creosote. They're acceptable for shoulder-season fires but are poor choices for extended cold-weather heating.

How Stove Efficiency Changes the Calculation

A traditional open fireplace converts only 10–25% of the wood's BTU content into room heat — most goes up the chimney. An EPA-certified wood stove achieves 70–80% efficiency.

If your calculator asks for stove efficiency and you have an open fireplace, use 15%. For a modern EPA-certified stove, use 75%.

This matters significantly: burning the same cord of oak in a fireplace vs. a wood stove produces 4–5× more usable heat from the stove. If you've been buying 8 cords per year for a fireplace, an efficient stove might reduce that to 2–3 cords.

Seasoning: Why Freshly Cut Wood Doesn't Count

Green (unseasoned) wood contains 50–60% moisture by weight. Dry seasoned wood is below 20% moisture. Burning green wood:

• Releases only 30–40% of the potential BTU
• Produces 4–6× more creosote than seasoned wood
• Can void insurance policies and stove warranties

Minimum seasoning time: 6–12 months for split hardwood stored under cover, out of contact with the soil. Dense species like oak need 12–24 months to fully season.

The calculator assumes seasoned wood. If you're burning green wood, expect to use 50–80% more volume to achieve the same heat.

How the Calculator Works

The calculator typically takes:

• Heating area (sq ft) — the space you want to heat
• Climate severity — approximated as heating degree days or a region selection
• Stove type and efficiency — fireplace, insert, or freestanding stove
• Wood species BTU value — or a general hardwood/softwood selection
• Percentage of heat from wood — 100% if it's your primary heat source, less if it supplements gas or electric

It outputs an estimated cord count for the heating season.

Common Mistakes

Confusing face cords with full cords. Face cords are ⅓ of a full cord. If a seller quotes you "three cords" at a suspiciously low price, confirm whether they mean full cords.

Calculating from green wood weight. A freshly cut cord weighs 2× a seasoned cord. Weight-based estimates are unreliable; always estimate in cord volumes and BTU.

Forgetting backup heat needs. Even experienced wood-heaters need backup for periods when you can't tend the fire — illness, travel, cold snaps when the stove can't keep up.

Not accounting for stove size. A small stove rated for 1,200 sq ft can't heat a 2,500 sq ft home even with the most efficient hardwood. Match stove output (BTU/hr) to your home's heat loss before estimating cord count.