How much stove fuel a backpacking trip needs is not a number you look up anywhere. It is a number you measure: your stove's burn rate in grams per hour, taken at the valve setting you actually cook at, times the hours the stove runs, times the boils you do per day, times the days out, plus a margin for cold and wind. Get the first two numbers from your own stove and your own pot and the rest is arithmetic. Skip that step and you are choosing between carrying dead weight and running dry on the second-to-last morning, and you will not know which one until you are out there.
I do this on the kitchen counter the night before a trip, and it takes about twenty minutes. The setup never changes. A digital scale that reads to a gram. A canister with at least one weekend already on it. A Sharpie and a strip of masking tape stuck down the side of the can where I write the date and the weight. That tape is the entire system. When I get home I weigh the canister again and write the new number underneath it. After three trips the tape is a record you cannot get from a spec sheet: how much a cold, windy weekend actually ate compared to a lazy car camp with the same stove and the same pot.
Burn rate is a measurement, not a spec
The published figure, when there is one, is usually the best case. Full valve, warm canister, still air, and whatever pot happened to be on the test bench. Some manufacturers publish burn time instead, in minutes per ounce of fuel, and you can convert that to grams per hour, but you are still converting somebody else's conditions into your units.
So measure it. Weigh the canister. Light the stove at the valve setting you actually cook at. For me that is a little past half, enough to hold a rolling boil under a lid without a roar. Let it run ten minutes by the clock, shut it off, let the canister come back to room temperature, and weigh it again. The difference times six is your burn rate in grams per hour. Run it a second time at full valve if you want both numbers, because they are not close to each other. A stove that sips at a simmer can be drinking two or three times as much with the valve wide open, and the mistake I see most is people planning around the wide-open number when they never cook that way. That estimate is safe. It is also how you end up carrying a canister of dead weight for four days.
Reading what is left in a canister
Canister fuel is sold by net weight in grams, and the gross weight is stamped on the side of the can. Gross minus net gives you the tare, the empty steel, and that number never changes. Multiply that by a kitchen scale and you have a fuel gauge: current weight minus tare equals fuel remaining. The tape on my canister is just that arithmetic worked out ahead of time so I do not have to remember a tare at six in the morning.
Boiling time is a separate number from stove power
This is where published specs mislead the most. Two stoves with the same claimed output can boil the same pot a minute and a half apart, because boiling time is about the whole system: how much water you started with, how cold that water was, how cold the air is, how much wind is hitting the pot, whether the lid is on, and how wide the pot is relative to the flame. Stove power is one input among six.
So I test the boil, not the stove. The pot goes out to the porch, in whatever weather is forecast, because a boil test in a warm kitchen is fiction. Two cups of water straight from the tap, thermometer if I am being careful, lid on, timed from the click of the igniter to a hard rolling boil. Then I do it again with the wind screen up and compare. The gap between those two numbers is the margin I write on the tape.
Tap water temperature is the sneaky variable. Water coming off a cold line in February can be twenty degrees colder than what comes out in July, and you pay to heat every one of those degrees. Cold ground water, cold air, and wind stack on top of each other. That is why the identical trip takes more fuel in the shoulder seasons than in midsummer.
Do the arithmetic
Say your boil came in at four minutes and your stove burned about 100 grams an hour at that setting. Four minutes is one-fifteenth of an hour, so that boil cost you roughly 6.7 grams.
Now count boils, honestly. This is the number people undercount, not the burn rate. Oatmeal is a boil. Coffee is a boil unless you are a cold-soak person. Dinner is a boil, and if it is a dehydrated meal you may be boiling more water than you think, because the package directions assume a hungrier person than you. Add a hot drink on a cold night and you are at three or four boils a day, not one.
At four minutes per boil, three boils a day runs about 20 grams. Divide the net fuel weight printed on your canister by that daily number and you have your days per canister. If the answer comes out shorter than your trip, you learn it in your kitchen instead of on a ridge.
Then add the margin, and be specific about what it is for. Cold mornings. A partner who wants tea. A day you get rained on and cook in the vestibule instead of on a rock. A boil that takes twice as long because the wind shifted around the ridge. I plan ten to twenty percent on a summer trip and closer to thirty in the shoulder season or above treeline. I have never once regretted the extra grams the way I have regretted not having them.
The canister that lies to you
Cold does something to a canister that feels exactly like being empty. Pressure drops, the flame goes soft and yellow, and the canister feels light and sounds hollow when you shake it. It is not empty. Warm it against your body or stand it in a bowl of lukewarm water if you are at home, let it come back to temperature, and light it again. Plenty of canisters get thrown out half full because of a cold morning.
The other half of that: a nearly spent canister loses pressure before it loses its last grams. The flame goes weak while there is still fuel in there. So no slosh is a signal, but a weak one. The scale is not.
Liquid fuel, long trips, and refills
White gas and other liquid fuels get measured in fluid ounces, not grams, and that changes your record keeping. A fuel bottle with molded markings, or a cheap plastic measuring cup that lives in your resupply box, lets you top off and know exactly what went in and what came out. The real advantage on a long trip is that you can carry exactly the volume your own arithmetic calls for between resupply points, with no partial canisters piling up and no guessing at the last one.
Canisters still make sense, and they get simpler the shorter the trip. One larger canister, one stove, no funnel, no pouring, no priming. For a weekend that simplicity is worth more than the weight you would save by getting the number perfect. On long trips with resupply the calculus flips. Smaller canisters you can swap out at a town stop beat one big one you have to haul over a pass, and refillable liquid fuel beats both, because you can buy precisely the volume your calculation says you need. Only the units change. The arithmetic does not.
What to do when the plan is wrong
It will be, sometimes. A cold snap, a stove that decides to run rich, a partner who boils a full liter for coffee. What matters is knowing which direction you are wrong in. If you measured conservatively, full valve burn rate and a generous boil time and real margin, then being wrong means extra weight in your pack. If you copied someone else's estimate off a forum, being wrong means cold food and no coffee at all. I know which failure mode I will take, and it is the one my shoulders complain about.
So the habit stays small. Weigh the canister, time a boil, do the multiplication, write it on the tape. Twenty minutes at the counter replaces the improvising you would otherwise be doing at 12,000 feet, and after a season of tapes you stop calculating at all. You look at the canister and you just know.
