The Warm Water Test

This works because liquid propane inside the tank keeps the metal cooler than the empty space above it. Pour warm (not boiling) water down the side of the tank from top to bottom, then run your hand down the same spot.

You'll feel the metal turn cold at the exact point where the liquid propane level sits inside. That cold line is your fill level — measure how far up the tank it is to estimate roughly how full you are.

Read the Gauge

Some cylinders, especially larger home and RV tanks, have a built-in float gauge that shows the percentage of propane remaining, similar to a fuel gauge. If your tank has one, it's the fastest way to check — just glance at the dial.

Smaller 20-lb grill cylinders typically don't have a built-in gauge, which is why the warm water test or weighing the tank works better for those.

Weigh the Tank

This is the most precise method. Every propane cylinder has two numbers stamped on the collar near the valve:

• TW (Tare Weight) — how much the empty tank weighs on its own.
• WC (Water Capacity) or the propane capacity in pounds — how much propane it holds when full.

Weigh the tank on a bathroom or luggage scale, then subtract the tare weight. The result is how many pounds of propane you have left. For example, if your tank weighs 25 lbs and the tare weight stamped on the collar is 17 lbs, you have roughly 8 lbs of propane remaining.