My gas invoice says SCM but the factor is per Nm3. Does the difference matter?
Yes, by about 5.5 percent. Indian gas bills state SCM at about 15 degrees C, while Nm3 is at 0 degrees C, so one SCM is about 0.947 Nm3. Convert the volume, or convert the factor, before you multiply. Using a per Nm3 factor on SCM volumes overstates CO2 by 5.5 to 5.7 percent.
Why the two volumes differ
Gas expands as it warms, so a volume means nothing without its reference temperature and pressure. A normal cubic metre (Nm3) is usually defined at 0 degrees C and 101.325 kPa. In India, PNGRB's regulations define a standard cubic metre (SCM) at 15.56 degrees C (60 F) and 1013.25 millibar, and some suppliers' terms, such as GAIL Gas's, use 15 degrees C, the ISO 13443 reference, at the same pressure.
At the same pressure, one SCM is 273.15 / 288.15 = 0.948 Nm3 at 15 degrees C, or 273.15 / 288.71 = 0.946 Nm3 at 15.56 degrees C.
How to convert
- Nm3 = SCM x 0.948 (SCM at 15 degrees C) or x 0.946 (SCM at 15.56 degrees C)
- SCM = Nm3 x 1.055 or x 1.057
- Factor per Nm3 = factor per SCM x 1.055 (or 1.057); factor per SCM = factor per Nm3 x 0.948 (or 0.946)
- If the pressure reference also differs, multiply by the ratio of the pressures as well.
Check the definition before converting
Read the definition on your bill or gas sales agreement. Some contracts state 15.5 degrees C, 20 degrees C or a different pressure. If the bill also prints energy in MMBtu or a GCV in kcal per SCM, calculate from energy as a cross-check; it does not depend on the volume reference.
What to write in the methodology note
State the unit on the invoice, its reference conditions, the factor's unit and source, and any conversion applied. An auditor checking a 5 percent gap will look for exactly this line.
Worked example: 10,000 SCM in a month
- Per SCM factor: 10,000 x 2.05 = 20,500 kg CO2
- Volume in Nm3: 10,000 x 273.15 / 288.15 = 9,479 Nm3
- Equivalent per Nm3 factor: 2.05 x 288.15 / 273.15 = 2.163 kg CO2 per Nm3; 9,479 x 2.163 = 20,503 kg CO2, the same answer within rounding
- Mistake: 10,000 SCM x 2.163 = 21,630 kg CO2, 5.5 percent too high
The example uses SCM at 15 degrees C; at 15.56 degrees C the mistake is 21,668 kg, 5.7 percent too high. 2.05 kg CO2 per scm is the IPCC 2006 based PNG factor Senseible uses.
What Senseible does here
Senseible applies its PNG factor of 2.05 kg CO2 per scm to the SCM volume printed on your gas bill, and shows the factor and unit on each line.
Sources: ISO 13443:1996, Natural gas, Standard reference conditions (iso.org), 2006 IPCC Guidelines, Volume 2 (Energy), Chapter 2, Table 2.2
Last reviewed 2026-10-19. SCM definitions from PNGRB regulations (15.56 degrees C, 1013.25 mbar) and GAIL Gas PNG terms (15 degrees C, 760 mm Hg); checked 2026-10-19. Check your own supplier's terms.