Weigh the tank and compare it to the tare weight stamped on the collar
Check the fuel level with warm water and feel for a temperature change on the tank side
Use a propane tank gauge or level indicator
Listen for a sloshing sound when gently tilting the tank
Observe whether appliances are losing pressure or going out
Check for frost or condensation lines on the tank, which may show remaining propane
If the tank has an automatic changeover regulator, inspect the indicator window or gauge
Verify the tank is no longer supplying gas by opening the valve briefly and checking for flow only if safe and appropriate
Have the tank professionally inspected or refilled if you are unsure