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How Much Does a Gallon of Propane Weigh?

Propane Conversions: Pounds, Gallons, BTU, Therms & ft³

"How Much Does a Gallon of Propane Weigh?"  is a very common question.
Many of the other questions ask about the various Propane conversion values in US gallons, pounds, BTUs, therms and cubic feet.
The easiest way to answer most of them is with a Propane conversion chart or table…

Propane Conversion Values

20 pound propane tankThe following are some of the most common propane conversion values:

First, what does a gallon of propane weigh?

♦ Propane Gallons to Pounds: 1 Gallon = 4.23 Pounds

♦ Propane Pounds to Gallons: 1 Pound = 0.236 Gallons (30.2 Ounces)

♦ Propane Gallons to Cubic Feet:  1 Gallon = 36.4 ft3 (Vapour/Gas)

♦ Propane Gallons to BTU:  1 Gallon = 91,502 BTU @ 60ºF

Propane Pounds to BTU:  1 Pound = 21,591 BTU @ 60ºF

♦ Propane  Cubic Feet to BTU:  1 cubic foot = 2,488 BTU @ 60ºF

♦ Propane Gallons to Therms:  1 Gallon = 0.915 therms

Note that all of the above are expressed in US Gallons.

Propane Conversion Charts

The charts below cover most of the common units of measure and gas bottle-cylinder sizes for the USA.
You can convert:
Propane Gallons to Pounds or Pounds to Gallons
BTU to Therms or vice versa
Propane Gallons to BTU or vice versa
Propane Pounds to BTU or vice versa
and all other combinations.

Imperial Gallons

Some countries use Imperial Gallons, which are about 20% larger than US Gallons.
To be exact, 1 Imperial Gallon ≈ 1.200950 US gallons
Note that most of these countries have converted to litres, in the metric system.

Gallons, Pounds, BTUs, Therms & Cubic Feet (ft3)

Propane Conversion Chart
Units of Measure
Equivalent Units
1 US Gallon
4.23 Pounds
(4 Pounds 3.7 Ounces)
1 Pound
0.236 Gallons
(30.2 Ounces)
1 US Gallon
91,502 BTU @ 60ºF
1 US Gallon
0.915 therm
1 cubic foot
2,488 BTU @ 60ºF
1 US Gallon
36.4 ft3 Gas
  Note: Some numbers have been rounded.

Propane Cylinder Sizes

Not surprisingly, when propane cylinder sizes are discussed, it is in imperial measurements.

This is because the USA uses the term 'Propane' in lieu of 'LPG'.

So, where LPG cylinder sizes are conveyed in kilograms, propane cylinder sizes are expressed in pounds.

Therefore, in the table below, the propane cylinder sizes are in pounds...

How Many Gallons in a 20 Pound Propane Tank?

20 pound propane tank
A 'full' 20 pound propane tank would contain 4.73 gallons of propane.
Note that in some US tank exchange programs, the fill is something less than 20 pounds and is labelled accordingly.
The image above is a typical 20 pound (9kg) propane tank.

How Many Gallons are in a 100 lb Propane Tank?

100 pound propane tank

23.64 gallons are in a 100 lb propane tank, based on the conversion chart above.
A 100 pound tank is roughly the same size as a 45kg gas bottle.
They are small enough to be exchanged or tanker filled.
The image to the right is of a typical 100 pound propane tank.

Background Information

Propane Specific Gravity - Density

Unlike water, 1 pint of propane does not weigh ≈ 1lb.  It actually weighs 0.51lbs.
This is because the density or specific gravity of propane is only about half that of water. 
Converting from weight to volume, 1lb of propane @ 60ºF has a volume of 0.24 US gallons.
Conversely, 1 US gallon of propane @ 60ºF only weighs 4.23lbs, instead of the 8.34lbs it would weigh if it was water.
Important Note:
All volumes are quoted in US gallons, as opposed to imperial gallons.
Imperial gallons are 20% larger.

Propane Gas Energy Content in BTUs

BTU is the acronym for British thermal unit.  It is a unit of energy.
One BTU is the amount of heat required to raise the temperature of 1lb of water by 1°F, at sea level.
Appliances are rated in BTU based on the required energy input. 
The relative efficiency of the appliance determines the heat output.
BTU's are used by propane companies to determine total gas load on a system when everything is running on maximum.
More propane energy content facts:

Propane BTU per Gallon

The following are the values for propane BTU per gallon and per ft3, as well as the values in therms and watts.
1 US gallon of propane = 91,502 BTU @ 60ºF
1ft3 propane gas = 2,488 BTU of Gas @ 60ºF
1 US gallon propane = 1.1 therm
1 therm = 100,000 BTU
1 watt = 3.41214 BTU/h

Propane BTU per Liter

Propane BTU per liter = 23,700 BTU per Liter

1MJ equals 948BTU, so to get an equivalent number of BTU, just multiply the MJ rating by 948.
1L = 25 MJ
So, to calculate propane BTU per liter:  25 MJ x 948 = 23,700 BTU
Combining metric and imperial measures is not typical but it can be easily calculated, as shown.

Propane Liquid to Gas Volume Expansion

Propane expands about 270 times in volume when it goes from liquid to gas. 
So, 1 US gallon of liquid propane equals 36.4 ft3 of gaseous propane

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.




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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.