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Let's first start with defining the two acronyms:
 - LPG is short for Liquefied Petroleum Gas
 - NG is short for Natural Gas

Although both gases are considered flammable and are hydrocarbon gases, LPG (or Liquefied Petroleum Gas) is actually propane (C3H8) and NG (or Natural Gas) is essentially methane (CH4). 

Just for the reader's information, Butane and Isobutane (C4H10) are also considered to be LPG gases.

The difference between LPG vs Natural Gas is:

  • different energy content,
  • different density,
  • different storage and delivery methods, and
  • the amount of air required for proper combustion.

Let's expand on the above:

  • As already discussed, LPG (propane) and natural gas (methane and propane) have different chemical formulas: Methane-natural gas formula is CH4 and Propane is C3H8.
  • LPG/propane has a calorific value of 93.2-MJ/m3, which is a higher energy content than the calorific value of natural gas which is 38.7-MJ/m3.
  • For proper combustion to occur, the air to gas ratio for LPG vs. Propane vs Natural Gas is approximately 25:1 while the air to gas ratio for natural gas is a 10:1 ratio.
  • LPG (propane) is more dense than air
    • Relative Density of Propane is 1.5219:1
    • Density of Natural Gas/Methane is 0.5537:1 
  • LPG (propane) can be compressed into a liquid and stored or transported in a cylinder or larger vessel.

A comparison of Physical Properties of the two gases:-

Gas Properties

Natural Gas
Chemical Formula C3H8 CH4
Energy Content: MJ/m3 93.2 38.7
Energy Content: BTU/ft3 2,572 1,011
Energy Content: MJ/kg 49.58 52.5
Boiling Temp oC -42.0 -161.5
Flame Temp o 1,967 1,950
Flame Temp oF 3,573 3,542
Specific Gravity 1.5219 0.5537
Density @ 15 oC: kg/m3 1.899 0.668
Caloric Value 93.2-MJ/m3 38.7-MJ/m3

Note: LPG is made up of propane, butane, isobutane or a mixture of the three.