Is LPG-Propane Heavier than Air? Lighter than Air?
LPG gas is not lighter than air.
LPG (propane) is heavier than air.
Butane is also heavier than air.
In fact, LPG is over 50% heavier than air at sea level (1 atm).
As a result, LPG gas will settle in low places.
LPG (Propane & Butane) is Heavier than Air
Is LPG (Propane & Butane)
Lighter or Heavier than Air
At standard temperature and pressure – STP¹ – LPG is a gas.
LPG gas (vapour) is heavier than air.
The following apply to LPG, as a gas:
● Specific Gravity of LPG gas is 1.55 (air = 1.00).
● LPG – propane – gas density is 1.55 times heavier than air.
● LPG weighs 1.898 kg/m3. Air weighs 1.225 kg/m3. (Both 15°C at 1 atm)
● LPG – propane – weighs 0.1162 lbs/ft3. Air weighs 0.0752 lbs/ft3.
● Butane, which is also considered LPG, weighs 2.5436 kg/m3 (15°C at 1 atm).
● Butane is 2.08 times heavier than air.
Note that LPG gas is also referred to as “LPG vapour”.
Vapour (vapor is the US spelling) is the more technically correct term.
Note that vapours are gases however not all gases are vapours.
¹STP – Standard Temperature and Pressure – is defined as 0°C (32°F) and 1 atm (14.7 psia or 0 psig)
Why It's Important to Know
In the event of an LPG gas leak, it is important to remember that LPG is heavier than air.
Leaking gas will settle to the lowest point, including basements and under houses.
Pits and drains are also obvious collection points.
So, if you have a leak, don't assume that all of the gas is gone just because you no longer smell it on the main level of your home.
Be sure that the gas has dissipated everywhere, even within the low spots inside and around your home.
LPG (Propane) Density – Specific Gravity of Liquid LPG
LPG is a liquid when stored under pressure in a cylinder or other vessel.
Unlike water, 1 kilogram of LPG does NOT equal 1 litre of LPG.
LPG – propane – density or specific gravity is about half that of water, with 1 litre equalling 0.51 kg (at 15°C).
So, 1kg of LPG has a volume of 1.96L.
Conversely, 1L of LPG (propane) weighs 0.51kg (at 15°C).
Expressed in USA units of measure, 1 lb of propane (at 60°F) has a volume of 0.24 US gallons.
Conversely, 1 US gallon of propane (at 60°F) only weighs 4.23 lbs, instead of the 8.34 lbs it would weigh if it was water.
Propane is 580.88 kg/m3 (at boiling point of -42°C or -44°F)
Butane is 601.26 kg/m3 (at boiling point of -0.4°C or 31.3°F)
The specific gravity (SG) of liquid Butane is 0.601 (at 25°C)
LPG Liquid to Gas or LPG Gas to Liquid
Note that the following are liquid to gas or gas to liquid conversions:
● LPG kg to m³ (1kg = 0.53m³) or m³ to kg (1m³ = 1.89kg)
● LPG litres to m³ (1L = 0.27m³) or m³ to litres (1m³ = 3.70L)
Comments, questions or feedback?
The information in this article is derived from various sources and is believed to be correct at the time of publication. However, the information may not be error free and may not be applicable in all circumstances.