Elgas LPG Gas Blog

LPG (propane) Gas Unit Conversions: Gas in kg, Litres, MJ, kWh & m³

Also Propane Gas Unit Conversion in Pounds, Gallons, BTU, Therms & ft³

We are frequently asked about the various LPG - propane - gas unit conversion (LP gas unit conversion) values.  The first table shown below covers most of the common units of measure and gas bottle-cylinder sizes for Australia, including kg, litres, MJ, kWh & m³ (e.g. LPG gas unit conversion of kg to litres is 1kg = 1.96L).

People ask the questions in many ways and the simplest way to answer most of them is with an LPG Gas Unit Conversion Table (or two). 

Litre (Liter) to kg & kg to Litres

The two most common conversions are litre (liter) to kg and kg to litre. It is important to note that water and LPG (propane) have different conversion formulas because they have different density.

Water Litre to kg: 1Litre = 0.999975 kg, so for all practical purposes 1L = 1kg

LPG (propane) Litre to kg: 1 Litre = 0.51kg

Water kg to Litre: 1kg = 1 litre

LPG (propane) kg to Liter: 1kg = 1.96 litres

LPG – Propane – Gas Unit Conversion Formulas (Metric):

  • LPG (propane) kg to litres: 1kg = 1.96L

  • LPG (propane) litres to kg: 1L = 0.51kg

  • *LPG (propane) kg to m³: 1kg = 0.53m³

  • ^LPG (propane) m³ to kg: 1m³ = 1.89kg

  • *LPG (propane) litres to m³: 1L = 0.27m³

  • ^LPG (propane) m³ to litres: 1m³ = 3.70L

  • LPG (propane) MJ to kWh: 1MJ = 0.278kWh

  • LPG (propane) kWh to MJ: 1kWh = 3.6 MJ

  • LPG (propane) litres to MJ: 1L = 25MJ

  • LPG (propane) MJ to litres: 1MJ = 0.042L

  • LPG (propane) kg to MJ: 1kg = 49MJ

  • LPG (propane) MJ to kg: 1MJ = 0.02kg

  • LPG (propane) litres to kWh: 1L = 6.9kWh

  • LPG (propane) kWh to litres: 1kWh = 0.145L

  • LPG (propane) kg to kWh: 1kg = 13.6kWh

  • LPG (propane) kWh to kg: 1kWh = 0.074kg

  • LPG (propane) L to BTU: 1L = 23,700 BTU

  • LPG (propane) kg to BTU: 1kg = 46,452 BTU

*Note that these are Liquid to LPG Gas unit conversions
^Note that these are LPG Gas to Liquid unit conversions
The second table covers most of the units of measure and gas bottle sizes for the USA including Pounds, Gallons, BTU, Therms & ft³.
You can convert all combinations of Pounds, Gallons, BTU, Therms & ft³.

Background Information

LPG Specific Gravity - Density

Unlike water, 1kg of LPG does NOT equal 1L of LPG.  
This is because the density or specific gravity of LPG is less than water. 
In Australia, where LPG is propane, 1kg of LPG has a volume of 1.96L. 
Conversely, 1L of LPG weighs 0.51kg.

LPG Gas Consumption in Megajoules

Megajoules per Hour (MJ/hr) ratings on appliances actually indicate the gas consumption of the appliance, not the output.  
It is often expressed as just MJ.  In the USA, they use BTU as the unit of measure.

Appliance Output in kWh

Kilowatt Hour (kWh) is how appliance output is measured. 3.6 MJ of input equals 1kWh of output at 100% efficiency. 
However, no gas appliance is 100% efficient. 
That is why we have Star Ratings, so we can compare relative efficiency between models. 
Appliance output is often expressed as just kW.

BTU to MJ Conversion

LPG energy content is expressed in BTU and MJ - Megajoules.

BTU, or British Thermal Unit, is another older measure of heat output based on the Imperial System.

As previously mentioned, BTU is used in the USA instead of MJ. 

One BTU is the energy required to raise the temperature of 1 pound of liquid water by 1°F, at sea level.  

1MJ equals 948BTU, so to get an equivalent number of Megajoules, just divide the BTU rating by 948. 

LPG (propane) BTU per Liter - LPG Energy Content

LPG energy content is expressed in BTU per litre. LPG - Propane BTU per liter = 23,700 BTU per litre

This is based on 1MJ equalling 948BTU, so to get an equivalent number of BTU, just multiply the MJ rating by 948

So, as 1L = 25 MJ then 25 MJ x 948 = 23,700 BTU per litre

LPG (propane) BTU per KG - LPG Energy Content

LPG energy content is also expressed in BTU per kg. LPG - Propane BTU per kg = 46,452 BTU per kg

Since 1kg of LPG = 1.96L, then based on the above 1.96 x 23,700 BTU/L = 46,452 BTU. So, 1kg = 46,452 BTU per kg

Combining metric and imperial measures is not typical but it can be easily calculated.

LPG Liquid to Gas Volume Expansion

LPG (propane) expands about 270 times in volume when it goes from liquid to gas. 
So, 1L of liquid LPG equals 270L of gaseous LPG. 
As there are 1000L in a cubic metre (m³), 1L of liquid LPG expands to 0.27m³.

LPG cubic meter to kg and LPG kg to cubic meter (m³)

When comparing LPG cubic meter to kg (m3 to kg) you are comparing LPG volume in its gaseous state (cubic meter) to the mass of LPG liquid (kg). To convert LPG cubic meter to kg you simply use the LPG conversion formula: LPG cubic meter (m3) = 1.8315 kg.

The more detailed explanation for LPG cubic meter to kg is one LPG cubic meter (m3) of gas equals to 1.8315 kg of liquid LPG (propane) at 25 °C (77 °F). LPG cubic meter to kg (m3 to kg) varies with temperature.

The same is true of kg to m³ conversion.

LPG kg to cubic meter: 1kg =  0.546 m3 (propane)

For butane LPG cubic meter to kg: 1kg = 0.4084 m3 at 25 °C (77 °F)

For butane LPG kg to cubic meter: 1m3 = 2.4486kg

Gas Bottle Tare Weight

Tare weight is the empty weight of the gas bottle-cylinder.  
Along with the gas bottle dimensions, they can vary greatly by manufacturer and date of manufacture. 
For example, older bottles tend to be heavier than more recent versions.

Measuring LPG by Pressure

When LPG (propane) is stored in a gas bottle, it is under pressure. 

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

The pressure is measured in kilopascals (kPa).

“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 pressure can vary greatly based on temperature.

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

As LPG is a liquefied gas, the pressure inside the cylinder will remain the same from full to empty (after the last of the liquid LPG is used), then the pressure will fall quickly as the last of the LPG vapour is used.

The use of Pressure as a measurement in LPG use is very limited. 

A steady Pressure only shows that liquid LPG is inside the cylinder, and not how much liquid is left.

In the US, pressure is measured in pounds per square inch (psi). 

Psi is defined as 1 pound of force applied per square inch.   As a comparison, 1 psi = 6.89476 kPa.

LPG (Propane) Gas Unit Conversion Table: kg, Litres, MJ, kWh & m³

LPG gas conversion value table with kg, litres, MJ, kWh and cubic meters.
Note that the m3 column refers to gaseous LPG

LPG Cylinder Capacity in Litres

LPG cylinder capacity in litres illustration shows full at 80%LPG cylinder capacity in litres goes from a small LPG cylinder capacity of 7.25 litres for a 3.7kg LPG cylinder to a large LPG cylinder capacity of 411 litres for a 210kg LPG cylinder. The chart below shows LPG cylinder capacity in litres for the 7 most popular sizes of LPG cylinder based on 1.96 litres of LPG cylinder capacity per kilogram (1kg = 1.96L).

LPG cylinder capacity in litres is considered full at 80%, to allow for ullage. Ullage is the empty LPG cylinder capacity at the top of the cylinder that provides room for expansion of the gas vapour.

See accompanying illustration of LPG cylinder capacity in litres full at 80%.

LPG Cylinder Capacity in Litres Comparison Chart

LPG Cylinder Capacity in Litres Chart

LPG Cylinder Size in kg

LPG Cylinder Capacity in Litres
3.7 7.25
8.5 16.6
15 29
18 35
45 88
90 176
210 411

This chart of LPG cylinder capacity in litres is based on propane at 1kg = 1.96L

The capacity of an LPG cylinder in litres can change if sold by the kg, as propane has 1.96L per kg whilst butane has only 1.724L per kg. This is because the two gases have different specific gravity.

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Propane Gas Unit Conversions Table: Pounds, Gallons, BTU, Therms & ft³

For our friends in the USA:

Propane gas unit conversion values in US gallons, pounds, BTUs, therms and cubic feet. The table below shown covers most of the common units of measure and gas bottle-cylinder sizes for the USA.

Propane Gas Unit Conversion Formulas (US Units of Measure):

  • Propane Gallons to Pounds:  1Gal = 4.23lbs

  • Propane Pounds to Gallons:  1lb = 0.24 Gallons

  • Propane Gallons to BTU:  1 Gal = 91,502 BTU

  • Propane Pounds to BTU:  1lb = 21,594 BTU

  • *Propane Gallons to ft3:  1 Gal = 36.38ft3

  • *Propane Pounds to ft3:  1lb = 8.59 ft3

  • BTU to Therms:  1 BTU = 0.000009993 Therms

  • Therms to BTU:  1 Therm = 100,067 BTU

*Note that these are Liquid to Gas unit conversions

Learn More About USA Units of Measure for Propane

Propane gas conversion tables for pounds, gallons, BTU, therms & ft3
Note that the ft3 column refers to gaseous propane

45 kg LPG Gas Bottles45kg gas bottle - cylinder

45 kg gas cylinder sizes are the most common size for home use

This is the size used for our Home Gas Bottle Exchange Service

They are also used with our Automatic Tanker Delivery Service

A typical installation has two 45kg gas bottles

Capacity: 88 litres

Diameter: 375mm

Height: 1250mm

 

90 kg LPG Gas Cylinders90kg LPG gas cylinder sizes / gas bottle sizes

90 kg gas cylinder sizes are the second most common size for home use

This size is commonly used with our Automatic Tanker Delivery Service

A typical installation has one cylinder

90 kg is also used with our Underground LPG Gas Storage System

Capacity: 176 litres

Diameter:  510mm

Height:  1380mm

 

210 kg LPG Gas Cylinders

210kg LPG gas cylinder sizes / gas bottle sizes

210 kg gas cylinder sizes are provided for high volume use

Larger storage vessels are also available, when needed

Filling is via our Automatic Tanker Delivery Service

Capacity: 411 litres

Diameter:  760mm

Height:  1450mm

 

 

 

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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.