The Petroleum Planning and Analysis Cell lists firewood at 4,750 kilocalories a kilogram, but the Intergovernmental Panel on Climate Change says 15.6 megajoules. Which heat value should I use?

The Petroleum Planning and Analysis Cell (PPAC) Ready Reckoner lists firewood at 4,750 kilocalories (kcal) per kilogram (kg), which is 19.9 megajoules (MJ). The Intergovernmental Panel on Climate Change (IPCC) default net calorific value is 15.6 MJ per kg. Charcoal, hard coal and lignite also sit inside the IPCC ranges.

The four fuels side by side

PPAC values from Table 9.1, converted at PPAC's own 1 kcal = 4.19 kilojoules. IPCC values are the Table 1.2 net calorific values in terajoules per gigagram, which equal MJ per kg, with the 95% range in brackets (the wood and charcoal ranges are IPCC expert judgement).

• Firewood: PPAC 4,750 kcal per kg = 19.9 MJ per kg. IPCC wood and wood waste 15.6 (7.90 to 31.0). PPAC is 27.6% higher.
• Charcoal: PPAC 6,900 = 28.9 MJ per kg. IPCC 29.5 (14.9 to 58.0). PPAC is 2.0% lower.
• Hard coal: PPAC 5,000 = 20.95 MJ per kg. IPCC other bituminous coal 25.8 (19.9 to 30.5), sub-bituminous 18.9 (11.5 to 26.0). PPAC is 18.8% below the first.
• Lignite-brown coal: PPAC 2,310 = 9.68 MJ per kg. IPCC lignite 11.9 (5.50 to 21.6). PPAC is 18.7% lower.
• Each PPAC figure falls inside the matching IPCC range.

What PPAC does not say

• The table is titled Average international Calorific Values of different fuels, yet these four rows sit under a heading marked India, with the source given as Indian Petroleum & Natural Gas Statistics from the Ministry of Petroleum and Natural Gas (MOP&NG).
• It does not say whether the values are gross or net, or at what moisture. IPCC's values are net.
• So the two columns are not guaranteed to describe the same fuel on the same basis. Part of the 27.6% gap on firewood is probably moisture and basis, though PPAC does not say.

Which one to use

1. A heat value from your own fuel test, on the basis you weigh the fuel, beats both.
2. With no test and an IPCC emission factor per terajoule (TJ), take the IPCC net value. The factor and the energy are then on the same basis. That is my reading of how to avoid mixing bases.
3. If you need energy in joules for a report and only PPAC's figure is to hand, use it, name PPAC and Table 9.1, and say the basis is not stated.
4. Pick one source and keep it for every year of the same fuel.

10 tonnes of firewood, carbon dioxide on both bases

• IPCC: 10,000 kg x 15.6 MJ = 156,000 MJ = 156 gigajoules (GJ)
• 156 GJ x 112 kg carbon dioxide (CO2) per GJ = 17,472 kg CO2
• PPAC: 10,000 kg x 19.9025 MJ = 199,025 MJ = 199.0 GJ
• 199.025 x 112 = 22,291 kg CO2
• Gap: 22,291 minus 17,472 = 4,819 kg, which is 27.6% more on the PPAC value

112,000 kg CO2 per TJ is IPCC's Table 1.4 default for wood. This CO2 is biogenic and goes on its own line outside Scope 1, as the firewood answer on this site explains. The gap changes that line, not the Scope 1 total.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records. Firewood and coal bills show tonnes or quintals, not heat value, so keep any fuel test report beside the records.

• Firewood bought by the quintal
• Indian coal emissions from GCV
• Lignite emission factor in India
• Furnace oil and kerosene heat values

Sources: PPAC Ready Reckoner 2025-26, Table 9.1 Average international Calorific Values of different fuels, IPCC 2006 Guidelines, Volume 2, Chapter 1 (Tables 1.2 and 1.4)

Last reviewed 2026-11-05. PPAC's table does not state a basis. If a later edition does, redo the comparison on that basis.