Proudly serving the Oil and Propane needs of northeast Oklahoma

The 80 Percent Rule: Why Your Propane Tank is Never Full

If you’ve ever gone out and checked your propane tank after a delivery, you might have noticed that your propane tank is never 100 percent full.

The one-word answer is safety.

Much like water, propane expands in the presence of heat. The difference between the two is how much propane expands. Propane increases in a volume to nearly 17 times the volume of water over the same temperature increase. If your tank is full and the temperature inside the tank rises, your tank becomes dangerous.

That’s why propane tanks are typically filled to only about 80 percent (slightly more in underground tanks, where the ground insulates the tank from big temperature swings). The extra space in the tank is a preventative measure – a cushion against the pressure that builds up in a tank when it’s hot. Our drivers use a fixed liquid level gauge to make sure we don’t overfill.

To calculate the approximate fill capacity of your propane tank, multiply the tanks total capacity by .8. Here’s a cheat sheet:








Ever wondered how we know what you can hold, here’s how:

To calculate the approximate amount in your tank, take the size of your propane tank and multiply by the percent in the tank. For example, a 500-gallon tank has 20% of propane, the formula is 500 x .2= 100 gallons.

Now to figure how much your tank will hold take the 80% gallons for your size tank minus the current amount in your tank. In our example, that would be 400-100=300 Gallons. Your tank can hold up to 300 gallons.propane tank

Maybe you are thinking, I can’t fill my tank each time that would cost too much. There is also a way that you can see how much propane will be in your tank if you order a lower amount. Take the amount of propane in your tank now (100 gallons) plus the amount ordered (let’s say 200). 100+200=300 gallons. Divide this number(300) by the tank size(500) and you will know what approximate percent your tank will go up to. 300 gallons/500 gallon tank= 60%.