How the firewood calculator works
Firewood is sold as a stacked volume that includes the air between the logs. In Europe the unit is the stère, one cubic metre of neatly stacked 1 m logs. In North America it is the cord, a pile 4 ft high, 4 ft deep and 8 ft long, or 128 ft³ (3.62 m³). Many sellers also quote a face cord or rick: a 4 × 8 ft face of logs of any length, which at the usual 16 in is one third of a full cord. The calculator measures your pile the same way, as length × height × log length.
Wood per season = heat needed ÷ appliance efficiency ÷ energy per stère (or per cord)For the season estimate it assumes seasoned wood below 20% moisture, which releases about 2,000 kWh of heat per stère for dense hardwood, 1,700 kWh for medium hardwoods and 1,400 kWh for softwood. The appliance efficiency then decides how much of that reaches the room: most of the heat from an open fire goes up the chimney.
Worked example
A pile 4 m long and 1.5 m high of 50 cm logs holds 4 × 1.5 × 0.5 = 3 stères, or 0.83 cord. A house that needs 8,000 kWh of useful heat from a modern stove at 75% must burn 8,000 ÷ 0.75 = 10,667 kWh of wood energy. With oak at 2,000 kWh per stère that is 5.3 stères, so the pile covers 56% of the winter. Burn the same wood in an open fireplace and the requirement jumps to about 27 stères, five times as much.
In the US, a stack 12 ft long and 5 ft high of 16 in logs is 60 ft² of face, which sellers would call 1.9 face cords; its true volume is 80 ft³, or 0.63 of a full cord.
Heat value by species
| Wood (seasoned) | Per stère | Per full cord |
|---|---|---|
| Oak, beech, ash, hickory | about 2,000 kWh | about 24–25 million BTU |
| Birch, maple, cherry | about 1,700 kWh | about 20–21 million BTU |
| Pine, spruce, fir, poplar | about 1,300–1,400 kWh | about 15–17 million BTU |
| Freshly cut wood, any species | roughly half of the above | water must be boiled off first |
By weight, all dry woods carry similar energy; dense species simply pack more mass into each stère, so a stack of oak lasts longer between refills than the same stack of spruce.
Buying and storing firewood
- Shorter logs stack tighter. One stère of 1 m logs cut to 50 cm settles to about 0.8 m³ of stacked volume, and to about 0.7 m³ at 33 cm. Check whether a price is per stère or per stacked cubic metre of the cut length.
- Ask for the full dimensions. A "load" or "truckload" has no fixed size. In most US states a cord is a defined legal measure, and a face cord is only valid if the log length is stated.
- Measure moisture. A cheap moisture meter on a freshly split face should read below 20%. Wet wood smoulders, wastes heat and coats the flue with creosote, a common cause of chimney fires.
- Season a year ahead. Split wood stacked off the ground, covered on top and open on the sides, needs about one summer for softwood and 18–24 months for oak.
- Keep the chimney swept. Have it inspected and cleaned at least once a year, and use a carbon monoxide alarm in any room with a stove.
Frequently asked questions
How many stères of wood do I need for a winter?
A stove used as the main heat source in a detached house typically burns 6–12 stères of hardwood a winter; a stove that only tops up central heating burns 2–4.
How many face cords are in a full cord?
With 16 in logs, three face cords make one full cord of 128 ft³. With 12 in logs you need four, and with 24 in logs only two.
How big is a cord of wood in cubic metres?
A cord is 128 ft³, which is 3.62 m³ of stacked wood, or about 3.6 stères.
How much does a cord of wood heat?
A seasoned hardwood cord holds about 24 million BTU. In a 75% efficient stove that gives roughly 18 million BTU of room heat, similar to 5,300 kWh.
Is it better to buy firewood by the stère or by weight?
Weight is fair only for dry wood, since water adds weight but no heat. Stacked volume is easier to check, as long as you know the log length and the wood is seasoned.
Last reviewed: 2026-09-27 · How we calculate