“Who cares, I just use my propane tank until it needs more propane, refill it, and rinse and repeat.” To be fair, if that’s the answer you had in the back of your brain to this question, we understand. How many gallons of propane in a 100 lb tank? That right there is a very common question, and you’d think that the number would just be displayed on each propane tank to end all headaches.

Well, it’s just not that simple. Now, with that being said, you’ll get a fairly straightforward answer to the aforementioned question when you Google it. In addition to the answer, you’ll get (and the answer that we’ll provide to you), there are also other factors and questions to assess that will help educate you even further on the matter. Let’s get the quick answer out of the way first, though.

How many gallons of propane in a 100 lb tank?

It all comes down to numbers and math when you answer this question. After all, when you do the math, propane weighs roughly 4.2 pounds per gallon. Factor in a 100-pound tank and the answer to the question would be right around 23.6 gallons. In reality, the number is going to be anywhere from 23 to 25 gallons. Virtually anywhere you look, this is the answer that you’re going to find.

So, that’s it, right? That’s all you needed to know and now you can get back to whatever you were doing before you came here, correct? Wait, we still need to waste (*cough) we mean use your time. All joking aside, there’s a lot left to discuss, and we think it’ll be beneficial for you.

Wait, why aren’t propane tanks 100 percent full?

Yep, propane tanks aren’t actually 100 percent full of propane, and it’s not to rip off customers. It really comes down to safety and logic. Reason being is that propane expands when it’s heated, and the extra space in the tank needs to be there to account for that. Typically, you’ll hear of the “80 percent rule,” and this just means that most tanks will be filled to 80 percent capacity.

The moral of the story is to just understand that a propane tank is never going to be completely filled with propane.

How long will a 100 lb tank last?

The old gas stove on fire
Photo by KWON JUNHO / Unsplash

Quite frankly, this question may be even more intriguing than, “How many gallons of propane in a 100 lb tank.” Propane tank owners around the world, after all, probably just want to know how long their tanks are going to last. Before we answer that, let’s point out something really nice about propane. The stuff just doesn’t go bad.

Propane isn’t like a lot of other fuel sources that are going to degrade over time, as it really doesn’t have an expiration date. In fact, the only real thing that owners need to worry about is the integrity and health of the tank itself. So, to address how long the propane itself will last, it’ll last a very long time.

Okay, but how long will it last if it’s being used? For that, you need to know a few variables. You need to know the burn rate of the appliance that’s using the propane and also the amount of propane that’s in the tank. Let’s break this down:

  1. Locate the tare weight (TW) on the propane tank (empty tank weight)
  2. Weigh the propane tank on a scale and subtract the TW from this value
  3. Divide by 4.2 (which is how many pounds a gallon of propane weighs)

The burn rate of one gallon of propane is estimated at around 92.000 BTUs. Find the burn rate of the appliance you’re using with the tank per hour.

  1. Take 92.000 (burn rate of propane) and divide it with the burn rate of your appliance
  2. Take the gallons left in the tank and multiply it by the hourly burn rate

This’ll determine how long the propane tank will last.

For the record, a few sources claim (for the last step) to take the gallons left in the tank and divide it by the hourly burn rate to get the answer. However, that doesn’t make any sense. Double-checking our math, and even looking at another source that said the same thing, multiplying the burn rate per hour to burn one gallon of propane by the amount of propane left in the tank will get the hours left that the tank will run.

We’re not trying to call anyone out here or anything. Believe us, we had to double-check that multiple times to ensure it was accurate. Math’s hard, are we right?!

Final thoughts

There, now if anyone ever asks you, “Hey, how many gallons of propane in a 100 lb tank?” or “How long will a 100 lb tank last?” you can set them straight. Then again, you may give them a headache if you attempt to explain to them the second question, but we digress.

And if we gave you a headache trying to explain that…we apologize! But, hey, there’s one thing that can probably make your headache better. No, we’re not talking about alcohol here, we’re talking about checking out some of the best propane generators on the market right now. Have a good one everybody.