Propane gas tank

Survival Math in Action: How Long Will Propane Last?

I was on a camping trip the first time I ran out of propane. Since there were plenty of other fuels around, I got along well enough.  My situation could have been much worse if I made the same mistake during a hurricane, major snow storm, or even during a major social collapse.  As a result, I realized that I wasn’t really ready for a camping trip, let alone a major crisis unless I found a good answer to the question “How long will propane last?”   This article includes information on how to figure out how long propane will last and also two ways to figure out how much propane you have in the tank even if you don’t have a gauge.

What Information do You Need?

  • The amount of time the propane will be used
  • The maximum number of BTUs used by the equipment in one hour
  • The estimated setting you will use the equipment at (ex. Will you  be using the device at ½, 1/3, ¼, 2/3, ¾ or full power?
  • Number of pounds or gallons of propane available in a full tank

Constant Values:

  •  Each pound of propane in the tank gives 21,600 BTU.  If you are using liquid propane, use 91,000 BTU.

Here are the steps to follow in order to find out how much propane you will need:

  • Start off by converting the amount of time the propane is to be used into minutes (unless it is already under 1 hour.  If you will be using the propane for 1 ½ hours, you would convert it to 90 minutes and so on.  In this example, let’s say I am using a propane lantern for 1 ¼ hours, so that means I would covert that to 75 minutes.
  • Determine how many BTUs will be used per hour based on the power setting of the equipment. In this case, let’s say my propane lantern uses 4854 BTUs per hour, but I am only going to use it at half power.  Divide by 2 to find out that the lantern will use 2427 BTUs per hour.
  • Take the number of adjusted BTUs per hour and divide by 60 to get the number of BTUs per minute.  In this example, 2427 divided by 60 is 40.45 BTUs per minute, which I will round up to 41 BTUs for the sake of simplicity.
  • Next, take the number of BTUs per minute and multiply it by the number of minutes that you expect to use the equipment.  In this example, I plan to use the lantern for 75 minutes, so I multiply 75 x 41 to get 3075 BTUs.
  • Since one pound of propane gives 21,600 BTU, I need less than a pound to run the lantern for 1 ¼ hours.  In fact, even if I only have one pound of propane in the tank, I can run the lantern at half power for just a little over 7 hours.

You can also use these methods from other websites:

Two Ways to Figure Out How Much Propane is Left

As you can see, it does not require Common Core math or anything complicated to figure out how much propane you will need to run any given piece of equipment.  But that doesn’t mean you are done with math because now you must also know how much propane is in the tank.  If you are anything like me, you gave up on gauges long ago because they never seem to be right.  Here are two ways that I use to figure out how much propane is in the tank and, from there, if I actually have enough for what I need:

Also see: Propane vs. Kerosene: A Storage Guide for Preppers

Method 1:  Each time I start off with a full tank of propane, I keep a tracking sheet that lists how much propane I use. Let’s before I decided to run a propane lantern, I used a cooking stove.  All I have to do is subtract that amount used from the number of pounds of propane in the tank to find out what is left.

Method 2:  This method requires a scale.  To begin take the TARE weight listed on the propane tank  (this is the weight of the tank with no propane in it and no other equipment attached to it).  Next, remove any devices you may have attached to the tank.  Place the propane bottle on the scale. Finally, subtract the TARE weight from the scale weight to see how many pounds of propane are in the tank.

Now that you know how to figure out how long propane will last regardless of tank size and usage level, it will be much easier to know how much propane you need.  What are your thoughts about using propane during long term and short term survival situations?  Do you feel that there are other, or better ways to figure out how long propane will last?  If so, please feel free to share your experiences in the comment section because I, and other freedom loving preppers are always learning and looking for better way to rise above all challenges associated with self-reliance.

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