Why Your Propane Tank Is Never Full

March 9, 2022 –

When your propane tank is “full,” it’s intentionally never truly filled to capacity.

It’s because reliable propane companies like Paraco know to leave room for propane expansion.

Propane expands when it meets heat. In fact, propane tanks typically expand to nearly 17 times the volume of water even when heated to the same temperature. This happens naturally as a result of the environment and weather.

So to allow for this natural expansion due to temperature changes, above-ground propane tanks and propane cylinders commonly known as “BBQ tanks” are filled to only about 80 percent. (The amount of propane that underground tanks can be filled with is slightly higher, since they’re insulated from large temperature fluctuations by the soil.)

Leaving that 20 percent of extra space in the tank is protective and preventative. Without leaving that space, when the temperature inside the tank rises, there’s a risk for danger.

The 20 percent of free space ensures that even if the propane tank gets hot, the propane inside has room to expand. This keeps it from creating so much pressure that its volume exceeds the tank’s capacity. Our drivers use a fixed liquid level tank gauge to make sure we don’t overfill.

To calculate the approximate fill capacity of your propane tank and see how many gallons of propane it can hold at “full,” multiply the tank’s total capacity by 0.8.

If you have any other questions about propane usage and safety, Paraco is here for you. We’ll help with all of your propane delivery needs, whether for your home or business, so get in touch with us when you’re ready.


  1. Gale Clinton on December 19, 2020 at 10:08 am

    My acct. says the usable capacity of my tank is 260 gallons, I thought a 500 gallon tank had a 400 gallon usable capacity?

    • Isousa on January 5, 2021 at 8:45 am

      Hello Gale! We checked out your account and the size of your propane tank is 320 gallons, with the 80% rule the usable capacity is 260 gallons!

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