Where the numbers come from
Heating water is one of the few things in outdoor planning with an exact answer. It takes about 4.186 kilojoules to raise one kilogram of water by one degree Celsius, and a litre of water is a kilogram. Taking a litre from 50 °F to boiling is a rise of 90 °F, which is 50 °C, so the water needs 4.186 x 50, about 209 kilojoules. That part is physics and no stove changes it.
What the stove changes is how much fuel it takes to deliver those kilojoules. A canister stove that puts 55 percent of the burner output into the pot needs 209 divided by 0.55, about 380 kilojoules of fuel. Isobutane blends carry roughly 46 kilojoules a gram, so that is about 8.3 grams for that litre. Start from near-freezing water instead and the rise is 180 °F, the water needs 419 kilojoules, and the same stove burns about 16.6 grams. Same stove, same pot, twice the fuel, purely because of where the water started.
Efficiency is the input worth measuring
| Condition | Effect on fuel |
|---|---|
| No lid on the pot | Steam carries energy straight out; the last stretch to boiling gets much slower |
| Wind across the burner | The largest single loss, and the reason two identical trips can differ by half a canister |
| Pot much wider or narrower than the flame | Flame licking up the sides heats the air, not the water |
| Boiling past the point the meal needs | Every extra minute at a rolling boil is fuel converted entirely to steam |
| Cold canister late in a trip | Pressure drops, output drops, the same meal takes longer |
You can measure your own figure in a kitchen in ten minutes. Weigh the canister, boil a measured litre from a measured starting temperature, weigh the canister again. The grams used, multiplied by 46 and divided by the kilojoules the water needed, is your efficiency in still air with everything going right. On the trail it will be worse, and knowing by how much is the useful part.
Rules of thumb and why they disagree
Published figures for canister gas run from about 8 grams per person per day to about 25, and everyone quoting them is telling the truth about their own trips. The low end is one hot drink from a warm source in summer. The high end is two hot meals and a drink from a near-freezing creek in wind. The physics above explains the whole spread without anybody being wrong, which is why entering your own water volume and starting temperature beats adopting a number.
Alcohol stoves change the arithmetic rather than the method. Denatured alcohol carries roughly 26 kilojoules a gram against 46 for gas, and simple alcohol burners are usually less efficient, so the fuel weight for the same boiling roughly doubles. That is fine for a two-night trip where the stove itself being three ounces lighter wins, and it loses badly by day six. The crossover point is arithmetic you can run on this page by changing two fields.
The container is dead weight
A 230 gram canister weighs about 335 grams full. The 105 grams of steel comes home whatever happens, and it comes home whether the canister is full or nearly empty. Two small canisters carry the same fuel as one medium one and about 80 grams more metal. Against that, a partly used canister of unknown contents is the most common reason people carry a spare, and a spare canister is 100 grams of metal you definitely did not need. Weighing canisters before a trip and writing the number on them with a marker settles the question and costs nothing.
Questions people ask
How much fuel per person per day for backpacking?
It depends mostly on how much water you boil and how cold it starts. Working from the physics: a litre and a half a day from 50 °F water at 55 percent stove efficiency is about 22 grams of canister gas per person per day. The same litre and a half from near-freezing snowmelt is about 25 grams. Wind can add half again on top. That is why published rules of thumb range from 8 to 25 grams and all of them are honest — they are describing different trips.
How many boils do I get from a 230 gram canister?
Divide 230 by the grams per litre this page works out for your conditions. At 8 grams a litre, which is warm water and a sheltered stove, that is around 28 litres. At 17 grams a litre, which is cold water in a breeze, it is around 13. The wide answer is the honest one: the canister does not know how many meals it is, only how many kilojoules it holds.
Do I need to boil water or just heat it?
For rehydrating a freeze-dried pouch, the instruction on the pouch is what matters and many of them ask for very hot rather than boiling water. Stopping at 190 °F instead of 212 °F from a 50 °F start cuts the energy for that litre by about a seventh, and that saving repeats at every meal. Whether water needs boiling for treatment is an entirely separate question with a different answer, and that one belongs to the agency managing the land and to your treatment method instructions.
Why does my stove use more fuel in the cold?
Two separate reasons that compound. The water starts colder, so it needs more energy to reach the same temperature — that alone can double the fuel per litre between a summer creek and snowmelt. And the canister itself gets colder, so the pressure inside drops, the burner delivers less heat, the boil takes longer and more of that heat escapes to the air around the pot while it is happening. The first effect is arithmetic you can put in the fields above. The second is why cold-weather stove choice is a different conversation.
Is alcohol or canister gas lighter for a week?
Canister gas, on fuel weight, by a good margin: alcohol carries about 26 kilojoules a gram against 46, and simple alcohol burners typically convert less of it. What alcohol wins on is the stove and the container, which can be an ounce or two against six or more for a canister setup with its metal. Short trips favour alcohol, long ones favour gas, and the switch point moves depending on how much you cook. Setting the energy content field on this page to 26 and the efficiency down to match runs the comparison with your own numbers.