Working how much LPG is left in a 45kg cylinder

The hot water method:

1. Fill a bucket or hot water kettle with hot water, the more water the better. 
2. Slowly pour the hot (not boiling) water down one side of the gas bottle, taking care not to scald yourself.
3. A visible line of condensation may form on the cylinder, indicating the gas level. If you don’t see a line: 
   Wait a few seconds, then run your hand down the same side of the bottle where you poured the water.
4. You should feel a distinct temperature change — the area below the gas level will feel noticeably cooler. The point where the temperature changes marks the level of the gas.
5. If you can’t feel any temperature difference, the bottle may be empty.

How does this work?

In Australia, LPG is propane, which is stored inside the cylinder under pressure as a liquid. When your appliances operate, this liquid boils into a gas that passes through the regulator. Boiling is an endothermic process, meaning heat is drawn from the steel cylinder. This causes the section of the cylinder containing liquid gas to feel colder.

When you check the gas cylinder level, this cooler area indicates where liquid propane is still present. The temperature change or the condensation that may form acts as a simple and effective gas cylinder gauge.

If gas is released rapidly, the cooling effect can be strong enough for ice to form on the outside of the cylinder, clearly showing the level of the remaining liquid gas.