How do I tell how much gas is left in my gas bottle?

You can use a simple method involving hot water to check how much gas is left in your gas bottle. Pour a cup of hot (but not boiling) water down the side of the bottle. As the hot water travels down, it will cool where the gas level is, as the gas inside the bottle absorbs heat and cools the metal. 

After pouring the water, run your hand down the side of the bottle. When you feel a noticeable temperature difference—where the bottle feels colder—this is the point where the liquid gas level is. The colder part of the bottle indicates the remaining gas. 

This method provides a quick and easy way to estimate your gas level without needing special equipment. Just be sure to use warm water, as boiling water is a safety risk.