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Home 9 Business LPG 9 LPG Properties – Physical Properties of LPG

LPG Properties – Physical Properties of LPG

22 Jun, 2026 | Business LPG, Residential LPG

In this article:

What are the physical properties of LPG: LPG properties include different gases, boiling point, vaporisation, chemical formula & more...

LPG Properties – Physical Properties of LPG

What are LPG Physical Properties? Define LPG Properties

LPG describes flammable hydrocarbon gases including propane, butane and mixtures of these gases.

What are LPG properties?

LPG properties include the chemical properties of LPG and the physical properties of LPG.

Included in the LPG properties are propane boiling point, LPG gas density, LPG fuel (LP gas fuel) energy content, flame temperature, propane chemical formula, expansion and more, when you define LPG properties.

What is LPG – Define LPG

LPG composition includes propane, butane & isobutane.

What is LPG?

LPG is primarily propane, butane, isobutane, and mixtures of these LPG fuel types.

LPG is produced during natural gas processing and petroleum refining.

LPG meaning describes flammable hydrocarbon gases.

LPG is liquefied through pressurisation as LPG in gas bottles.

The typical constituents of LPG are propane and butane. The propane formula (formula propane) is C3H8 and the butane formula is C4H10.

When you define LPG in different countries, the supply of LPG can be propane, butane or propane-butane blends.

In NZ, LPG is a propane-butane mix.

In Australia, LPG is just propane.

LPG exists as liquid or gas (vapour) as LPG in gas bottles, depending on pressure and temperature.

Natural Gas Liquids – NGL – have the same LPG composition plus a few more gases not normally included in LPG.

The full NGL list includes ethane, ethene, butylenes, propylene, propene, isobutene, butadiene, pentane, pentene and pentanes plus, as well as propane, butane and isobutane.

Define LPG – Definition of LPG

LPG stands for “Liquefied Petroleum Gas”, a flammable hydrocarbon gas that is a mixture of propane and/or butane, when you define LPG.

It is used primarily as a fuel for hot water, heating, cooking, and vehicles.

LPG is stored as a liquid under pressure and transported in gas bottles or cylinders.

What are LPG Properties?

As an answer to what are LPG properties, they include:

  • Propane boiling point - LPG (Propane) VaporisationPropane boiling point (boiling point for propane)
  • Butane boiling point (boiling point for butane)
  • LPG gas density
  • LPG composition – components – constituents
  • Propane formula – propane chemical formula
  • Butane formula – butane chemical formula
  • LPG boiling point
  • LPG flame temperature
  • autoignition temperature of LPG
  • LPG flash point
  • LPG gas pressure
  • LPG gas odour
  • Appearance of LPG
  • Energy content of LPG
  • LPG gaseous expansion
  • Combustion formula of LPG
  • LPG gas limits of flammability
  • LPG nomenclature
  • LPG molecular weight
  • Propane formula (formula propane) is C3H8 and the butane formula is C4H10

We’ll review these most commonly referenced LPG properties…

LPG Properties Chart

LPG Properties Chart
Propane formula (formula propane)
C3H8
Butane formula
C4H10
Propane Boiling Point (boiling point for propane)
-42 °C  or  -44 °F
LPG Melting – Freezing Point
-188 °C  or  -306.4 °F
Specific Gravity of Liquid LPG
0.495 (25°C)
Liquefied Petroleum Gas Density
1.898 kg/m3 (15°C)  or  0.1162 lb/ft3
Energy Content of Liquefied Petroleum Gas
25 MJ/L or 91,547 BTU/Gal (60°F)
Liquefied Petroleum Gas Gaseous Expansion
1 L (liquid) = 0.27 M3 (gas)
Propane Flame Temperature
1967 ºC  or  3573 ºF
Limits of Flammability
2.15% to 9.6% LPG/air
Autoignition Temperature
470 °C  or  878 °F
Molecular Weight
44.097 kg/kmole
  Note: Some numbers have been subject to rounding.
 

LPG Boiling Point – Propane Boiling Point (Boiling Point for Propane)

What is LPG boiling point or propane boiling point (boiling point for propane)?

Water boils at 100°C or 212°F, becoming a gas (steam).

In contrast, of LPG – propane boiling point (boiling point for propane) is -42°C or -44°F, becoming gas vapour.

LPG stays liquid because it is under pressure in a gas cylinder.

As a liquid, LPG looks a lot like water.

LPG is colourless and odourless in its natural state.

LPG Density & LPG Specific Gravity

What are LPG density and LPG specific gravity? Define LPG density and specific gravity.

LPG gas density (propane) is 1.55 times heavier than air at 1.898 kg/m3 vs 1.225 kg/m3 for air (both 15°C at sea level).

LPG (propane) liquid is about half that of water at 495 kg/m3 (25°C) vs 1,000 kg/m3 (4°C) for water.

Specific gravity of propane and water is 0.495 (25°C) and 1.000 (4°C), respectively.

 

What is LPG Density – What is LPG Specific Gravity for Liquid LPG

Unlike water, 1 kilogram of LPG (propane) liquid does NOT equal 1 litre of LPG
 
LPG gas density or specific gravity is about half that of water, at 0.51.
 
Where LPG is propane, 1kg of LPG has a volume of 1.96L.
 
Density of LPG - PropaneConversely, 1L of LPG liquid weighs 0.51kg.
 
1 gallon of liquid propane weighs 4.24 pounds.
 
The specific gravity (SG) of liquid propane is 0.495 (at 25°C)
 
Propane is 580.88 kg/m3 (at propane boiling point)
 
The specific gravity (SG) of liquid butane is 0.601 (at 25°C)
 
Butane is 601.26 kg/m3 (at butane boiling point)
 

Propane Formula – Formula for Propane

Propane Chemical Formula – Chemical Formula Propane

Propane Molecular Formula (Molecular Formula Propane)

The propane chemical formula (propane molecular formula) is C3H8

The propane formula (formula for propane) means each molecule of propane consists of three carbon atoms and eight hydrogen atoms.

Propane Structure – Propane Structural Formula- Structure Propane

Propane structural formula (propane structure) can also be written as CH3CH2CH3

Propane Molar Mass – Molar Mass of Propane

Molecular Mass of Propane – Propane Molecular Mass

The molar mass of propane (propane molar mass) C3H8 is approximately 44.1 g/mol.

The molecular mass of propane (propane molecular mass) is calculated by totaling the molar mass of three carbon atoms (3 x 12.01 g/mol) and eight hydrogen atoms (8 x 1.008 g/mol).

 

LPG Density as a Gas: LPG – Propane is Heavier than Air

The LPG density as gaseous propane is 1.898 kg/m3 (at 15°C and sea level).
 
LPG is heavier than air1 ft3 of LPG (propane) gas weighs 0.1162 pounds.
 
Butane is 2.5436 kg/m3 (at 15°C and sea level)
 
In contrast, the density of Air is 1.225 kg/m3 (at 15°C and sea level).
 
So, LPG gas density is heavier than air.
 
Note that LPG gas is also referred to as LPG vapour, which is the more technically correct term.
 

12 Important Liquefied Petroleum Gas – What are LPG Gas Facts You Should Know

1. LPG is the acronym for liquefied petroleum gas or liquid petroleum gas.

2. LPG is a group of flammable hydrocarbon gases liquefied through pressurisation and stored as LPG in gas bottles.

They are, in most cases, used as LPG fuel.

3. LPG comes from natural gas processing and petroleum refining.

4. There are a number of gases that fall under the “LPG” label.

We define LPG as propane, butane and isobutane (i-butane), as well as mixtures of these gases.

5. LPG gases are compressible into liquid at low pressures and stored as LPG in gas bottles.

6. The common uses for LPG include use in gas heating, cooking, hot water and vehicles.

LPG is also utilised in refrigerants, aerosol propellants and petrochemical feedstock.

7. LPG is stored, as a liquid, in steel vessels ranging from small BBQ gas bottles to larger gas cylinders and LPG in gas storage tanks.

8. “Wet gas” is a term that is sometimes used to describe LPG, as a result of its liquidity.
 
9. An alternate reference for LPG is as a Natural Gas Liquid – NGL.
 
10. In nature, propane does not occur alone.
 
11. LPG – propane boiling point is -42°C or -44°F, becoming gas vapour.
 
12. The propane formula is C3H8 and the butane formula is C4H10.
 

What is an LPG Name? LP Gas = Propane

Propane molecule

In NZ, LPG is a propane-butane mix.

In Australia, LPG is propane.

What is a name other than LPG?

We can also define LPG as: LPG Gas, LP Gas, LP Gas Fuel, Propane, BBQ Gas, Camping Gas or Autogas.

LPG can be other gases in other countries.

Propane is a three carbon molecule with the formula C3H8.

The illustration shows a model of the molecule.

What is LPG Temperature: Flame, Boiling Point, Melting/Freezing Point

What are LPG gas temperature includes flame temperature, propane boiling point and LPG freezing temperature.

LPG temperature also affects the pressure of LPG in gas bottles.

LPG Gas Temperature - Flame TemperatureLPG flame temperature (when burned with air) is 1967ºC or 3573ºF.

LPG (propane) gas boiling temperature is -42°C or -44°F, as compare to water at 100°C or 212°F

LPG boiling point is where liquid propane boils and becomes vapour (gas).

LPG (propane) gas melting/freezing temperature is at -188°C or -306.4°F.

So, LPG temperature for freezing is a much lower temperature than water, which freezes at 0ºC.

What is LPG Pressure?

As mentioned before, LPG is stored in gas bottles under pressure.

The term “LPG pressure” refers to the average force per unit of area that the gas exerts on the inside walls by the LPG in gas bottles.

LPG Gas Pressure – LP Gas Temperature Chart shown)

LPG Pressure-Temperature Chart

LPG pressure measurement is in kilopascals (kPa) or pounds per square inch (psi).

“Bar” is yet another unit of measure for pressure.

1 Bar = 100 kPa, so it is metric based but not an SI unit of measure.

LPG gas pressure can vary based on temperature, as shown in the chart.

The level of LPG gas fill in the gas bottle comes into play when the LPG is in use, as it affects the rate of vapourisation.

LPG is a liquefied gas.

So, the LPG gas pressure inside the cylinder will remain the same from full until the vaporistion of the last of the liquid LPG.

Then the LPG gas pressure will fall, with the use of the last of the LPG vapour.

 

Odourant Added for Safety – What are LPG Odorants

LPG Odourant Added for SafetyWhat are LPG odorants? The most common LPG odorant is ethyl mercaptan.
In its natural state, LPG is an odourless gas.
 
The distinctive smell that people associate with LPG is actually added to it as a safety measure.
 
Without the addition of an LPG odourant, leaking LPG could collect without detection.
 

LPG Hazards of Direct Contact – Cold Burns

Always use caution to avoid direct contact exposure, as liquid LPG is cold enough to cause severe cold burns on exposed skin.
 

LPG Energy Content – Propane

LPG fuel (propane) contains approximately 25MJ per litre.
 
This also converts to 6.9kWh.
 
One gallon of propane contains 91,547 BTU (60°F).
 

LPG Calorific Value of ‘Water Gas’

The calorific value of the LPG gas used to heat water is no different than liquefied petroleum gas LPG fuel (LP gas fuel) used for other applications.
 
So, once again, ‘water gas’ contains 25MJ per LP gas litre or 91,547 BTU (60°F) per gallon.
 

LPG Gaseous Expansion Ratios

LPG Gaseous expansionLPG expands to 270 times the volume when LPG goes from liquid to gas.
 
So, 1L of liquid LPG (propane) equals 270L of gaseous LPG.
 
As there are 1000L in a cubic meter (M3), 1L of liquid LPG expands to 0.27M3.
 

What is an LPG Combustion Formula Equation

In the presence of enough oxygen, LPG burns to form water vapour and carbon dioxide, as well as heat.
 
LPG combustionPropane Formula Equation for Complete Combustion of LPG:
 
Propane formula (formula propane) for complete combustion in words: Propane + Oxygen → Carbon Dioxide + Water + Heat
 
Propane formula (formula propane) for complete combustion in symbols: C3H8 + 5 O2 → 3 CO2 + 4 H2O + Heat
 
Incomplete combustion of LPG occurs when not enough oxygen is present.
 
Incomplete combustion of LPG results in the production of water, carbon monoxide, and carbon dioxide.
 

What is an LPG Equation for Incomplete Combustion of Propane?

Propane Formula Equation for Incomplete Combustion of LPG:
 
Propane formula for incomplete combustion in words: Propane + Oxygen → Carbon Dioxide + Carbon Monoxide + Water + Heat

Propane formula for incomplete combustion in symbols: 2 C3H8 + 9 O2 → 4 CO2 + 2 CO + 8 H2O + heat.

 

LPG Flame Temperature – Propane Flame Temperature

An LPG (propane) flame burns at 1980°C.
 
When LPG is burning properly, the flame is blue.
 
A yellow or red flame is usually indicative of incomplete LPG combustion.
 

What are LPG Limits of Flammability

The lower and upper limits of LPG flammability are the percentages of LPG that must be present in an LPG gas/air mixture.
 
This means that we define LPG limits of flammability as between 2.15% and 9.6% of the total LPG gas/air mixture must be LPG gas in order for it to be combustible.
 

LPG Flash Point Temperature

The flash point of LPG (propane) is  -104°C or -156°F.
 
We define LPG flash point as the minimum temperature at which propane will burn on its own after ignition.
 
Below this temperature, LPG will stop burning on its own.
 
However, if a source of continuous ignition is present, LPG will burn below  -104°C.
 

LPG Autoignition Temperature for Propane & Butane

Autoignition temperature is the lowest temperature at which LPG will spontaneously ignite in air.
 
This is without an external source of ignition, like a spark or flame.
 
The LPG autoignition temperature decreases as the pressure or oxygen concentration increases.
 
The autoignition temperature of LPG – Propane – is 470 °C or 878°F.
 
LPG – butane autoignition temperature is 405°C or 761°F.
 

LPG Gas Dissipation

LPG gas is heavier than air and will sink to and collect at the lowest point.
 
If vented to the outside air, LPG will dissipate with the slightest movement of air.
 
With LPG gas vented into a sealed structure, with no air movement, the LPG gas will collect on the floor. LPG gas will rise toward the ceiling, as more LPG gas enters into the structure.
 

LPG Molecular Weight for Propane – Butane – Isobutane

The molecular weight for LPG – Propane – is 44.097 kg/kmole.
 
The molecular weight for Butane (n-butane) is 58.12 kg/kmole.
 
For Isobutane (i-butane), the molecular weight is the same as for n-butane at 58.12 kg/kmole.
 

LPG Vapour (Gas) Use vs. Liquid Use

Liquid LPG in the bottom of the gas bottleLPG supply is either liquid or vapour.
 
The difference is in the LPG gas extraction from supply cylinder or vessel.
 
Most LPG applications use LP gas vapour.
 
Appliances such as water heaters, room heaters and cookers all use LPG gas vapour.
 
If these appliances were to have liquid LPG flow to their burners, the result could be a fire or similar safety hazard.
 
This is why LP gas cylinders should always be upright, so that any LPG gas released is in vapour form only.
 

What are LPG Things You Didn’t Know – 6 Facts

While you may know some of these LP gas (liquid petroleum gas) facts, chances are you don’t know all of them.

Have a read and learn more about:

1. Real LPG Explosions are Really Rare

2. Simulated Natural Gas from LPG

3. The Source of LPG

4. LPG gas is NZ-Australian Made Energy

5. LPG is a Renewable Energy Source

6. LPG is NOT Coal Seam Gas (CSG)

1. LPG Gas Cylinder Explosions are Extremely Rare

Hollywood and the media would have you believe that LPG gas cylinder explosions are a common event.

In fact, LPG gas explosions are quite rare and it is quite difficult to even make an LPG gas cylinder explode on purpose.

Most gas explosions are the result of gas leaking into a confined space, like a kitchen.

This is no more likely with LPG than with piped natural gas.

Often, the gas bottle itself is not even involved in the event, as LPG gas bottles are always stored outdoors.

2. Simulated Natural Gas from LPG

Most people have never even heard of Simulated Natural Gas (SNG) let alone know that it can be made with LPG.

Mixing vapourised LPG gas with air produces SNG.

We can use SNG in place of natural gas, as it has near identical combustion characteristics.

It can be used alone or mixed with regular natural gas.

There are no changes required in burners, regulators or gas jets.

There are a number of reasons to use SNG:

•  To help meet peak demand when natural gas supplies are inadequate

•  To operate while in preparation for the start-up of a natural gas supply

•  As a stand-by in the event of a natural gas supply disruption

Simulated natural gas has a few names.

Besides SNG, it is also called propane-air and LPG gas-air.

3. What are LPG Sources

Many people mistakenly think of LPG as a by-product.

In reality, LP gas is a valuable co-product produced from gas fields and crude oil refining.

They process the gas stream from natural gas fields to separate the gases present.

These include methane, ethane, propane, butanes and pentanes.

Impurities are also removed, including water.

The produced gases are each funneled into their own supply streams.

They capture propane and butane, the two common types of LPG, and store them in their liquefied form.

The same is true of crude oil refining.

The refinery process creates many co-products.

The co-products include gasoline, diesel fuel, asphalt base, heating oil, naphtha, kerosene and LPG gas.

4. What is LPG Autogas?

LPG is the only motor fuel in which NZ and Australia are self-reliant.

Unlike both petrol and diesel, for which NZ and Australia rely on imports, we produce more LPG gas than we consume.

Not only are we completely self-sufficient in LPG but we are also a net exporter of LPG.

5. What is an LPG Renewable Energy Source – Liquefied Petroleum Gas

LPG is now a renewable energy sourceLPG has gone from being a traditional fossil fuel to a new form of renewable energy.

Scientists have created a genetically engineered version of the common E. coli bacteria.

This version produces propane (LPG).

So, LPG is now a renewable energy.

The bacteria consume sugar.

With genetic modification, and the help of a couple of enzymes, they make propane.

The propane produced is chemically identical to regular propane.

6. LPG is NOT Coal Seam Gas (CSG)

There is some confusion over what Coal Seam Gas (CSG) is and what it is not.

LPG is not CSG.

While CSG may contain various gases, typical CSG is 95% to 97% pure Methane.

LPG is not Methane.

LPG is Propane.

Eric Hahn
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