Posted: June 16, 2025
It’s not unusual for us to hear from a customer who’s new to propane to call us after a delivery to find out why the gauge on their tank indicates that it’s not completely full. It’s a good question—and we get it: If you’ve called us to come fill your tank, why isn’t it full? The reason has to do with how propane responds to changing temperatures.
Propane, also called LPG or liquid propane gas, is transported and stored in a liquid form. If you paid attention in high school chemistry, you might remember that liquids expand when they are heated. What you may not know is that liquid propane expands a lot more, and a lot faster, than some other liquids. In fact, propane will expand nearly 17 times more than water that is heated the same amount.
Because of the way propane expands, we follow what we call “the 80% rule.” For your safety, an aboveground propane tank, which is exposed to the sun, is considered “full” at about 80% to provide a cushion against the pressure that builds up inside the tank. Underground tanks are typically filled to about 85% because they are insulated.
Remember, although your tank will never be filled to more than 80%, you should always call for a fill-up before your tank falls below 20% so we have time to schedule a delivery. If your tank falls below that level, you could lose pressure, which can lead to problems with equipment.
If you have an above-ground propane storage tank, the gas gauge is right at the top of the tank, under a lid or dome. If you have an underground tank, the gauge will be near the fill pipe.
You’ll see a gauge that looks a lot like a speedometer, with numbers going around the edge, and a single pointer. The numbers indicate what percent of gas is in your tank.
Keep in mind that the amount of gas in the tank doesn’t actually change when propane expands or contracts—only its density does. As a result, you might notice that the tank gauge reading fluctuates slightly during quick temperature swings (hot day, cool night), but don’t worry, that’s perfectly normal.
Of course, it’s good to know how to check your tank level, but you have enough on your to-do list. That’s why we give you easier ways to make sure you get propane deliveries when you need them—without having to remember to check your tank and call us for delivery.
We know you’re busy—with plenty of things on your to-do list besides checking your propane tank gauge. That’s why Superior Gas offers two convenient services to help.
Customers love our automatic delivery service, which uses a proven algorithm to calculate when you will need a propane delivery. Not only does it eliminate the need to call for a delivery, but it makes things easier on our end, too: We’re better able to plan customer deliveries, using the most efficient routes to get to everyone quickly. That saves time and money—savings we can pass on to you.
For seasonal homeowners—and anyone who’s propane use fluctuates a lot—we recommend our wireless propane monitor. It tracks the level of propane in your tank in real time, and transmits your usage via wireless cellular technology. When the tank gauge reaches a pre-set level, the monitor alerts us—and you—directly via a wireless mobile app.
Whether you opt for automatic delivery service or will-call, we believe in old-fashioned customer service. We’re always happy to take your call and answer any questions. Contact us to order propane or to become a customer today.