Is Your Propane Running Low? How to Check Without Guessing

The worst time to discover you’re low on propane is in February at 10 PM when the furnace stops kicking on.

Checking your tank level takes about 30 seconds once you know how. Here are four methods, from free to $40, in order of reliability.

Method 1: Read the Gauge (If You Have One)

Most above-ground propane tanks 100 gallons and larger have a float gauge on top, it looks like a small dial, usually with a red needle, and shows a percentage from 0 to 100 (or sometimes 10 to 90, since suppliers generally won’t fill above 80% to allow for expansion).

If the needle is above 30%, you’re in good shape for normal use. Below 20%, call your supplier. Below 10%, call your supplier today.

The catch: gauges stick. A float gauge that hasn’t moved in weeks is probably stuck, not accurate. Tap it gently with a finger before trusting it. If it doesn’t move at all, don’t trust the reading, use one of the methods below.

Method 2: The Warm Water Trick (Free)

This one works on any tank and costs nothing.

Pour warm (not boiling) water down the side of the tank. Run your hand along the metal from top to bottom. The section of tank that has propane in it will feel noticeably cooler than the empty section above it, propane absorbs heat from the metal. The line where it transitions from cool to warm is your approximate fill level.

It takes a minute to feel the difference. On a cold day the temperature contrast is less pronounced, but it still works. On a very hot tank (direct sun all day), it’s harder to read.

This is a good check when your gauge seems stuck or you just want to confirm what you’re seeing.

Method 3: A Propane Tank Scale or Dial Gauge ($10–$25)

For small tanks (20 lb grill tanks), the easiest method is a scale. The tank has a tare weight stamped on the collar (the empty weight). Weigh the tank, subtract the tare, and what’s left is propane, 1 lb of propane = roughly 0.24 gallons.

For larger tanks (100–500 gal), an inline gauge that threads onto the valve is more practical than a scale. These gauges connect between the tank valve and the regulator and give you a constant pressure reading. They’re not perfectly precise, but they’re better than a sticky float gauge.

Bayou Classic Propane Gauge, around $15, widely available, works on standard tanks. Fine for grill-tank users who want to stop guessing mid-cook.

Method 4: A Smart Tank Monitor ($35–$50)

This is the one worth buying if you heat your home with propane.

A Bluetooth tank monitor attaches to the outside of the tank, no plumbing, no valve threading, and uses an ultrasonic sensor to measure the level inside. Pair it with a phone app and you get a percentage reading whenever you’re in Bluetooth range, plus low-level alerts.

Mopeka Pro Check Universal, about $40, works on standard vertical tanks from 20 lb up through large residential tanks. The app is reliable, the sensor lasts years on a coin battery, and it installs in two minutes with a magnet or strap. This is what I use.

If you want wifi range (check from anywhere, not just Bluetooth distance), SteelHead Systems TankCheck and similar monitors connect to your home network, but they cost more and require a hub or bridge.

For most homeowners, the Mopeka’s Bluetooth range, good from inside the house if the tank is close to an exterior wall, is enough.

What Level Should You Call For a Delivery?

Most suppliers recommend calling at 20–25%. That gives them time to schedule a delivery before you’re in emergency territory, and it protects you from running out during a cold snap when trucks are backed up with other customers.

Running completely empty is a bigger deal than it sounds. When a propane tank runs out, the system loses pressure and pilot lights on all your appliances go out. Before you can use anything again, a tech needs to come out, refill the tank, re-pressurize the system, and relight the pilots. That’s an additional service call, often at an emergency rate, on top of the delivery cost.

The 20% threshold is there for a reason.

Auto-Delivery vs. Will-Call

If you’re on auto-delivery, your supplier uses a degree-day formula to estimate when you need a fill and schedules it automatically. You shouldn’t run out, but you’re also not in control of timing, and you’ll sometimes get deliveries when you don’t strictly need them.

If you’re on will-call, you call when you need a delivery. You have more control over timing and can shop for better prices between fills. The risk is on you, if you forget to watch the gauge, you can run out.

A tank monitor is especially valuable on will-call, because it removes the guesswork and gives you a timely prompt without requiring you to go outside and check.

One More Thing: The 80% Rule

Propane expands significantly with heat, up to 17 times the volume of liquid. Because of this, your supplier will never fill a tank to 100%. The standard is 80%, which leaves a vapor space at the top for safe expansion.

So if your 500-gallon tank shows 80% after a fill, that’s a full fill, roughly 400 gallons. Don’t call asking why they left space. That’s correct and required.

---

Checking your level takes 30 seconds with a working gauge or the warm water method. If you’re heating a home with propane, the $40 Mopeka monitor is worth it for the peace of mind alone, especially heading into winter.

Related Reading

• Best Propane Tank Monitors and Gauges (Reviewed)
• Propane Cost Guide: What You Should (and Shouldn’t) Be Paying
• How to Switch Propane Suppliers