Rare is the backpacking trip where the last gasps of gas are used on the final boil on the final day. This is why most of us have at least a couple of part-used canisters sitting around the house, possibly more. While it may not wholly prevent such an accumulation, one of the first steps in gear and fuel management is to weigh and mark canisters both before and after a trip.
Returning from a multi-day hike this month I then spent the usual couple of days sorting out gear. Cleaning, reproofing and drying mostly. One brief task to be completed was a reweigh of my gas canister to establish how much fuel I used over a six day November backpacking trip. It helps with my guestimation on fuel requirements in the future. Every hike is different- different ambient temperature, different elevation, different wind speeds, different types and quantities of meal and drinks prepared, even different gas stoves. But still, I gain a deeper understanding on MY likely needs. It may help you in your planning if you did similar if you do not already.
It starts as soon as you buy a gas canister. Weigh and mark the full/gross weight on it. While I have often found a little variance between exact same canisters following purchase, I am not quite at the stage where I take my digital scales to the shop but sometimes I feel tempted when I get home and weigh the canisters as I do feel just a tad aggrieved with 10g or more difference between canisters supposed containing the same (expensive) quantity of fuel.
It is a useful practice to mark canister weights on the side or base with a sharpie. Not all canisters are equal and there is some variance between similarly sized canisters. The mid-sized canisters with around 220g of gas can vary from 130g to 160g when empty. While it doesn’t cover all gas canisters, there is a useful table here. But that is just one set of weights. I repeat, exact same canisters can vary, if only by a handful of grams.
I have written before on how it is possible to refill many lindal valve type gas canisters with fuel, though the practice is not recommended by almost all stove and gas canister manufacturers. That said, many backpackers will do it. Either as a means of bringing together fuel from part used canisters, or as a way of saving cost by transferring into a small canister, fuel from a larger one.
I have written before on a couple of handy little devices with which it is possible to refill gas canisters. One small and cheap, the other larger and far more expensive. It is a potentially hazardous procedure and many might prefer not to do it. Particularly as just about all lindal valved gas canisters carry the words DO NOT REFILL writ large on their side.
If you do refill gas canisters it may be well to limit the number of times you do so. Additionally recording on the base of the canister each time you refill it. I use the letter ‘R’ and a five bar gate system. Limiting myself to five refills of any particular canister. Some might choose to trust their canister and its valve for further refills. Also note on the canister if you have changed from a propane (winter) mix to a pure butane fill so that you are aware that the mix is less suited to colder weather. Finally, we are advised (by G-Works) that it is advisable to only refill a gas canister to 80% of it’s stated capacity.
So what did my recent re-weighing of a gas canister reveal? Not a great deal perhaps. 145g of fuel used over six days in November. i.e.- lots of hot meals and hot drinks. That suggests to me that a small cartridge will be insufficient for ME over a similar hike, with the same stove on a future November backpacking trip and I should continue to rely on my larger canister.