Posted: June 9, 2025
Smart shoppers always check the invoice: You look at your credit card statement to make sure there are no suspicious charges, you look at your check after a dinner out to make sure you aren’t paying for someone else’s drinks or entrees. And every so often, a customer—usually one who’s new to propane—will call us after a delivery to ask why the gauge on their tank indicates that it’s not completely full. It’s a valid question—we get it: If you’ve called us to come fill your tank, why isn’t it full?
The first thing we tell them is that they’re correct. And we reassure them that we haven’t charged them for more gallons of propane than we delivered. And then we explain the science behind a propane tank “fill-up.”
If you paid attention in chemistry, you know that liquids expand when they are heated. What you may not know is that propane, also called LPG or liquid propane gas, is transported and stored in a liquid form. What’s more, liquid propane expands a lot more, and a lot faster, than some other liquids. Propane will rapidly expand nearly 17 times more than water heated the same amount. So for safety, we leave some room in the tank.
An aboveground propane tank, which is exposed to the sun, is considered “full” at about 80%. That provides a cushion against the pressure that builds up inside the tank. Underground tanks are typically filled to about 85% because they are insulated.
Keep in mind that the amount of gas in the tank doesn’t actually change when propane expands or contracts—only its density does. You might notice that the tank gauge reading fluctuates slightly during quick temperature swings (hot day, cool night). Don’t worry, that’s perfectly normal.
We know you’re busy—with plenty of things on your to-do list besides checking your propane tank gauge. That’s why we offer two convenient services to help. Automatic delivery uses a proven system based on your previous usage and factors like average temperatures and weather forecasts to let us 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 deliveries, using the most efficient routes to get to everyone quickly. That saves time and money—savings we can pass on to you.
If your 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.
If you opt to call us for a delivery, 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.
Find out why so many families and businesses across Northwest and Central Ohio and West-Central Indiana trust Mercer Landmark for friendly service, transparent pricing and reliable propane deliveries.
Contact us for more information and to become a customer today.