Firewood Calculator

Firewood estimation relies on volume and heat output to determine how much wood you need for a full heating season.

A cord of firewood is the standard unit of measurement: a neatly stacked pile measuring 4 ft × 4 ft × 8 ft = 128 cubic feet. A face cord (or rick) is the same height and length but only as deep as one log (typically 16 inches), so it equals roughly one-third of a full cord.

How this calculator works

There is a textbook way to do this and a practical way, and they give the same answer while asking very different amounts of you.

The textbook way is BTU accounting: heating days × your stove’s hourly output × hours burned per day, divided by the BTU in a cord of your species. Correct, and it needs four numbers most people do not have to hand, starting with how many hours a day they actually run the stove.

The practical way, which is what the inputs above use, works from a monthly burn rate:

Cords = Monthly rate × Months × Heating role × Wood factor

• Monthly rate by stove size: 0.4 cords for a small stove, 0.65 for a medium, 0.9 for a large. These are what a stove of that size gets through in a month when it is doing the heating.
• Heating role: full rate as a primary heat source, half for supplemental, a fifth for the occasional evening fire.
• Wood factor: hardwood 1.0, mixed 1.2, softwood 1.5. Softwood carries roughly a third less heat per cord, so you burn correspondingly more of it.

The two methods agree. A medium stove running as primary heat for five months on hardwood comes to 0.65 × 5 = 3.25 cords here; the same stove at 60,000 BTU/hr for 8 hours a day over 150 days on 26 million BTU oak comes to 2.8. The gap is the difference between “8 hours a day, every day” and how a stove really gets used.

BTU output by stove size:

• Small stove (40,000 BTU/hr): ~2–3 cords/season
• Medium stove (60,000 BTU/hr): ~3–5 cords/season
• Large stove (80,000+ BTU/hr): ~5–7 cords/season

BTU per full cord by wood species:

• Oak: 24–28 million BTU (excellent, long burn)
• Hickory: 25–28 million BTU (very dense, slow burn)
• Maple: 22–25 million BTU (great all-rounder)
• Ash: 20–24 million BTU (splits easily, burns clean)
• Birch: 20–23 million BTU (good, burns faster than oak)
• Cherry: 18–22 million BTU (pleasant aroma)
• Pine: 15–18 million BTU (fast burn, more creosote risk)
• Poplar: 13–16 million BTU (low density, best for kindling)

Worked example: You heat your home 150 days/year using a medium stove (60,000 BTU/hr) burning 8 hours per day. You use seasoned oak (26 million BTU/cord).

Daily BTU = 60,000 × 8 = 480,000 BTU/day Season BTU = 480,000 × 150 = 72,000,000 BTU Cords needed = 72,000,000 ÷ 26,000,000 = ~2.8 cords

Add 10–15% buffer for cold snaps, and always buy seasoned wood (dried at least 6–12 months). Green wood loses 30–40% of its heat value.