There’s no doubt that isobutane fuel canister stoves are so popular because they are easy to use, clean burning, and have a low stench factor. But, at the same time, they’re relatively bulky and heavy compared to just carrying a fuel bottle. And one of their more irritating characteristics is that we’re often unsure how many we have to carry on any given trip. Sure, we’ve all seen specs for “1.5 hours on high”, or the like; but at what ambient temperature, and what if you actually cook with your stove rather than just boiling water?

Our standard fuel canister for testing stoves is the MSR IsoPRO 8 ounce. While we haven’t actually done a full test of different brands of canisters, the MSR has performed well at all times, and is the most consistently available at different stores in our area. So, we grabbed a new one and headed into the field with it. We boiled water in the morning for our coffee and tea; we cooked eggs for breakfast; we heated water for washing up; we sauteed little trout we caught for lunch along the way; we cooked dinner–sometimes several courses for dinner. Sometimes it was on high, sometimes medium, and sometimes even on as low as we could make it go to avoid burning something.

And, we intentionally used different stoves; after all, this was a test of the way the fuel canister would work in the real world, not the test of a particular stove/pot combination. So, a Jetboil Sol and MSR Reactor were pressed into service for heating water; a Primus Express was the choice for general cooking duties; and when the temperature dropped below freezing, we inverted the canister on a Coleman Fyrestorm Ti using the Powermax Fuel Adapter and used it as liquid fuel. We used the same canister in hot weather, then took it back out in cool weather in the early fall, then back one more time for a winter backpacking trip.

And, each time, we timed our use of it from the moment we turned it on to the moment we turned it off, and then scratched the time into the paint on the canister (okay, we started with a Sharpie, but decided that was a dumb idea, particularly the first time the canister was wet).

And…the answer is? Total run time for all uses was 3 hours, 1 minute, 29 seconds. Quite a difference from the typical run time spec given on a stove’s box; those tend to be closer to an hour. Now, if you’re a Ramen ultralighter who only boils water to make those noodles soft enough to slurp, you won’t get even close to that much time out of a fuel canister. But, for those of us with mixed uses, it makes it pretty clear that for a few nights out, we don’t need 3 fuel canisters. And, knowing that 8 ounces of fuel is typically going to last us around 3 hours, and that the empty canister weighs 4.6 ounces, it gives us a guide for what we can expect from a partially used fuel canister. We weigh them before a trip and mark the amount of fuel; if it weighs 9.7 ounces, we’ve got roughly 5.1 ounces of fuel. Each ounce of fuel is good for about 23 minutes, so that canister’s got better than an hour and a half left of our “typical” use.

Is this a highly scientific method? Nope, and it frankly can’t be, as the way you use a fuel canister will obviously affect its lifespan. We might get 4 hours out of one, and 2 out of the next. You might always get 3, or 2 or 1.5 out of yours, But…at least it’s a guide that helps figure out how useful those partially used canisters are…it’s better than hefting one and guessing that it might be a quarter full and that might be good for…10 minutes? 10 hours? Since we started this project, we’ve found that we’re more confident taking our partials on trips without QUITE as many backup bottles. Give this a try with one of your canisters, and we’re betting you’ll feel the same way!