How Many Calories in Firewood? Oak Firewood Heat Value and the Highest-Calorie Wood?

Short answer: according to Forest Research, the UK forestry research agency, oven-dry wood has a net calorific value of about 19 MJ/kg, roughly 4,540 kcal/kg, and dry species differ little. Moisture makes the real difference: wood at 20% moisture gives about 3,510 kcal/kg, fresh wood at 50% about 1,980 kcal/kg. Oak wins by volume, not by weight.

Current prices and types: Oak firewood prices →

How many calories in firewood? A table by moisture content

These are net (lower) calorific values from Forest Research's calorific value versus moisture spreadsheet; moisture is on a wet basis. kWh/kg = MJ/kg ÷ 3.6; kcal/kg = MJ/kg × 1,000 ÷ 4.1868 (rounded to tens).

From 20% to 50% moisture, the heat in a kilogram of wood roughly halves. Forest Research likewise says a fresh green log has only about half the energy of a well-seasoned one.

How many calories in oak firewood?

Per kilogram, not much different from other wood. Forest Research's technical supplement says there is little variation in calorific value between species tested at the same moisture content. The same document gives freshly felled oak a moisture content of 47% and 2,635 kWh per tonne, roughly 2,270 kcal/kg (2.635 × 860). Oak dried to 20% gives about 3,510 kcal/kg, as in the table.

The moisture figures on our products are the sack declarations: 15-20% for dry oak firewood and 25-30% for 6-month oak firewood. On the Forest Research table, dry oak lands at roughly 3,510–3,770 kcal/kg, 6-month oak at roughly 3,000–3,260 kcal/kg. Keep drying 6-month wood at home and the gap closes: how to dry firewood.

Which firewood has the highest calorific value?

By weight they are almost equal. According to Michael Jacobson of Penn State, pound for pound softwoods (such as pine) have more heat value, but per unit volume they give about half the heat of dense hardwoods. A firebox fills by volume, so volume is what matters.

The USDA Wood Handbook gives a specific gravity of 0.68 for white oak, 0.64 for American beech and 0.35 for eastern white pine (oven-dry mass, volume at 12% moisture). So a cubic metre of oak holds about 680 kg of dry wood, the same volume of that pine about 350 kg. With Forest Research's typical values at 20% moisture, a cubic metre of hardwood holds about 2,670 kWh and softwood about 1,890 kWh. Species by use: oak, beech or pine.

What are the properties of oak firewood?

• Density: oak is a hard, dense wood; the same weight takes up less space.
• Burn time: according to Forest Research, dense woods burn longer, so you top up the stove less often.
• Drying: fresh oak is around 47% moisture. The EPA recommends at least 6 months of seasoning, Penn State a year or more.
• Lighting: softwoods are easier to light (Forest Research); start oak with pine kindling.

How many calories in charcoal?

According to FAO's charcoal-making guide, the energy of 1 tonne of charcoal is equivalent to about 7,260 kWh, or to 1.65 tonnes of dry wood at 15% moisture. 7.26 kWh/kg × 860 ≈ 6,240 kcal/kg. The same guide gives a gross calorific value of 32,500 kJ/kg on a dry basis for a charcoal sample made from oak (≈ 7,760 kcal/kg). For barbecues, see how to light barbecue charcoal. Stove coal carries more heat per kilogram (Forest Research: house coal 7.5–8.6 kWh/kg); to compare, see wood or coal in a stove and how many calories coal should have.

What does it depend on?

• Moisture: the biggest factor; between 20% and 50% the heat per kilogram roughly halves.
• Density: sets the heat per volume; oak is far more wood than pine in the same space.
• Unit of sale: whether you buy by weight or by stere; for conversions see how many steres in 1 tonne of firewood.
• Stove efficiency: how much heat reaches the room depends on the stove and chimney.

For a rough estimate of your seasonal needs use our fuel calculator, and see all types on our firewood page.

Safety: burn only dry wood

Wood, like coal, produces carbon monoxide. The CDC describes it as an odourless, colourless gas; Türkiye's Ministry of Health lists headache, dizziness and weakness as the first signs. If you suspect it, open the windows, leave the room and call 112. See stove gas symptoms and carbon monoxide detectors.

Frequently asked questions

How many calories in 1 kg of firewood?

It depends on moisture: air-dry wood at 20% gives about 3,510 kcal/kg (4.09 kWh/kg), fresh wood at 50% about 1,980 kcal/kg.

What is oak wood ash good for?

Per Oregon State University Extension, wood ash contains small amounts of potassium and phosphorus, carries calcium and magnesium and raises the pH of acidic soil. Use no more than 10 pounds per 100 square feet a year (roughly 0.5 kg/m²); keep it away from acid-loving plants such as blueberries, azaleas and rhododendrons and from soil above pH 7. Cool ashes in a lidded metal container at least 10 feet (3 m) from the house (USFA).

Why does wet wood give less heat?

The water has to evaporate before the wood burns, and that uses heat. According to Forest Research, wet logs smoulder, make tar and smoke and increase the risk of a chimney fire.

Does beech or oak give more heat?

Per kilogram they are very close if dried to the same moisture. Their Wood Handbook densities are also close (0.64 and 0.68); dryness is what decides.

Sources: Forest Research, “Typical calorific values of fuels”; Forest Research, “Moisture content” and calorific value vs moisture spreadsheet; Biomass Energy Centre, “Wood as Fuel – Technical Supplement”; “Wood as Fuel”; USDA FPL, Wood Handbook (FPL-GTR-190), Table 5–3a; Penn State, Michael Jacobson; FAO, Simple technologies for charcoal making, chapter 1 and chapter 10; Oregon State University Extension, “Use fireplace ash sparingly”; EPA Burn Wise; USFA Heating Fire Safety; CDC, carbon monoxide; Ministry of Health, CO poisoning.