Got enough gas? There are a few ways to find out. The easiest is to shake your canister – if there is gas inside, you'll hear it moving around. Easy!
If you're not sure how much is there you may want to weigh your gas cylinder – the weight of the bottle without any gas in it is listed on the outside. If you're hovering down near that number (in most cases, 8.5kg) chances are you're going to need to change it over. How much it weighs is how much gas you have – genius!
If you don't have any scales handy, do the hot water test. Just grab a jug of hot water and pour it over the bottle. Run your hand down the canister until it feels cold, and that's the level the gas is at. Voila!