Which is right for turning gas volume into energy: 25.2 standard cubic metres per million British thermal units, or 37,000 British thermal units per standard cubic metre?

Both appear in the Petroleum Planning and Analysis Cell (PPAC) Ready Reckoner, and they differ by 7.3%. The 25.2 standard cubic metres (SCM) per million British thermal units (MMBtu) figure assumes 10,000 kilocalories (kcal) per SCM. The 37,000 British thermal units (Btu) per SCM figure works out to about 9,324 kcal. Your bill's printed energy beats both.

Where each figure sits in the Ready Reckoner

• Table 9.5, Natural Gas Conversions, credits GAIL (India) Ltd. It gives a gross calorific value (GCV) of 10,000 kcal per SCM, net calorific value (NCV) at 90% of GCV, and 1 MMBtu = 25.2 SCM at 10,000 kcal per SCM, with 1 MMBtu = 252,000 kcal. A gas import table elsewhere in the document repeats the 25.2 SCM approximation.
• In the table of gas transport lines, a note listed against one operator, coded PIL, reads: Conversion factor of 37000 Btu/SCM is used for computing volumes in MMSCMD, meaning million standard cubic metres a day. The table row for the Kakinada to Bharuch line names its operator, so my reading is that the note belongs to that operator. The document does not say so.
• Table 9.1 gives India's average natural gas production as 8,000 to 9,480 kcal per SCM.

The arithmetic that links them

1. 25.2 SCM per MMBtu is 1,000,000 Btu / 25.2 = 39,683 Btu per SCM. That is 10,000 kcal, since 252,000 kcal / 1,000,000 Btu = 0.252 kcal per Btu.
2. 37,000 Btu per SCM is 37,000 x 0.252 = 9,324 kcal per SCM, or 1,000,000 / 37,000 = 27.03 SCM per MMBtu.
3. 39,683 / 37,000 = 1.0725, so the 25.2 basis gives 7.3% more energy from the same volume.
4. 9,324 kcal sits inside the 8,000 to 9,480 production range. 10,000 kcal sits above its top. That comparison is mine; PPAC does not draw it.

What this does to your figures

• A carbon dioxide (CO2) factor per SCM, such as 2.05 kilograms (kg), does not use either conversion, so it is unaffected.
• Any route that goes from SCM to energy to CO2 moves by 7.3% depending on the basis. Pick the basis from your bill, not from whichever table you opened first.
• If the bill prints a calorific value or the energy in MMBtu, use that. It describes the gas you were sold. If it prints only SCM, state which basis you used and keep it for every month and every year.

10,000 SCM on a bill with no calorific value

• 25.2 basis: 10,000 / 25.2 = 396.8 MMBtu
• 37,000 Btu basis: 10,000 x 37,000 / 1,000,000 = 370.0 MMBtu
• Gap: 396.83 minus 370.0 = 26.83 MMBtu, which is 7.25% of 370.0 (396.83 / 370.0 minus 1), about 7.3%
• To gigajoules (GJ) at 252,000 kcal x 4.19 = 1,055.9 megajoules per MMBtu: 419.0 GJ and 390.7 GJ
• At NCV 90% and 56.1 kg CO2 per GJ: 419.0 x 0.9 x 56.1 = 21,155 kg CO2, against 390.7 x 0.9 x 56.1 = 19,725 kg CO2
• Direct route at 2.05 kg per SCM: 10,000 x 2.05 = 20,500 kg CO2, between the two

The 56.1 kg per GJ is the Intergovernmental Panel on Climate Change (IPCC) 2006 default for natural gas on a net basis. The 90% ratio is PPAC's own NCV to GCV figure. 1 kcal = 4.19 kilojoules is PPAC's conversion. PPAC does not say whether 37,000 Btu per SCM is gross or net; this example treats it as gross, like the 25.2 figure, and applies the 90% to both.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records. Check whether your gas bill prints a calorific value or energy in MMBtu. That printed figure is better than either conversion here.

• PNG bill in SCM or MMBtu to CO2
• India natural gas GCV per SCM
• SCM or Nm3 on a gas invoice
• Gas meter reading against a PNG bill

Sources: PPAC Ready Reckoner 2025-26, Table 9.5 Natural Gas Conversions, Table 9.1, the gas import table note and the gas transport table notes, IPCC 2006 Guidelines, Volume 2, Chapter 1 (Table 1.4, natural gas)

Last reviewed 2026-11-05. The 37,000 Btu note is attached to one operator's row in PPAC's table. If a later edition drops or explains it, update the page.