‘How much stove fuel should I carry?’ It’s a question that almost every outdoorsman has asked themselves. If you pack too much fuel, you’ll end up carrying unnecessary weight, and if you pack too little, you might end up trying to cold soak your last dehydrated meal (not ideal). There are, of course, many other articles with suggestions on how to calculate your fuel needs for a trip, but all fall short in one crucial aspect: they don’t factor in the fuel needed to keep water boiling once it has been brought to a boil (as you would when cooking dehydrated meals). The calculations used in this article do just that – take into account extra cooking time – to give you a more accurate idea of how much fuel you need on a trip. This method is easiest to use with canister and liquid fuel stoves, which generally have specified boil time and burn times (or at least the volume of water boiled with a given amount of fuel), but it can also be used with alcohol stoves if you are prepared to conduct a test to determine out how much water you can boil with an ounce of fuel.
- Definitions
- Plan your meals
- The maths
- Environmental factors that affect fuel efficiency
- Activities that contribute to fuel consumption
- Tips for saving fuel
- How to calculate the amount of fuel in a canister
When is it important to calculate how much fuel you need?
Some people might be tempted to estimate their fuel needs, and in some situations that’s okay. The question is when is it okay to estimate your fuel needs and when is it wise to calculate how much fuel you need? The most obvious instance in which it makes sense to estimate your fuel needs is when you can make an accurate estimation based on past experience with the same stove in similar conditions. When using a stove for the first time or under different conditions, you have no point of reference, so it makes more sense to do the maths.
The two other instances in which you would want to calculate your fuel needs are those in which you are trying to save weight and only want to carry as much fuel as is necessary and conditions in which your safety depends on you having enough stove fuel. You don’t want to underestimate your fuel needs when it’s consistently going to be below freezing and you need to heat food and water for hot drinks just to keep warm.
Definitions
Before we get into the maths, it would be useful to look at four definitions and two important distinctions: that between boil time and burn time; and that between water brought to a boil and water kept at a boil.
Boil time
Boil time tells you how fast a stove can bring a specified amount of water to a boil in ideal conditions. Some manufacturers specify the time needed to boil a liter of water and others specify the time needed to boil half a liter of water. For the calculations used later in this article, you need to know the time taken to bring a liter of water to a boil. If your stove’s boil time is specified in anything other than minutes per liter, you will have to do an extra calculation in step one.
Burn time
Burn time refers to the length of time a stove will burn for when used with a canister of a certain size. Manufacturers conduct their tests under lab conditions (ideal), and the chances are that your stove will boil a little less water than spec’d, even if conditions are favourable. Some manufacturers specify their stoves’ burn times while others specify the amount of water boiled using a canister of a certain size. If you only have the latter, you can still work out the burn time by multiplying the amount of water boiled by the stove’s burn time.
Water boiled
This is the total amount of water brought to a boil over the course of a trip. Besides helping you to calculate total boil time and the amount of fuel that you will use over a trip, knowing the amount of water you will boil or use for cooking and making hot drinks is also useful for working out how much water you need to carry between water sources.
Plan your meals
Before you can figure out how much fuel you’ll need, you have to figure out how much water you are going to bring to a boil and then keep at a boil. If you are only going to boil water for hot drinks and freeze-dried meals, the maths will be pretty simple. If, on the other hand, you are going to actually cook your food (dehydrated meals and those made from dry ingredients), you will also need to factor in the fuel used to keep the water boiling while the food cooks. As already explained above, I suggest using a table of estimates (above) for converting water kept at a boil to water brought to boil. Although not absolutely accurate, this does make it much easier to arrive at an estimate for total water boiled (actually a representation of the amount of fuel you will use). In my meal plans, I put these figures in separate columns. The figure in the second column is water kept at a boil, a figure which comes straight from the table above.
| day | meal | food | calories | water boiled |
| Friday | snack | trail mix (200 g) | 460 | - |
| dinner | pasta (150 g) with dried sauce | 600 | 500 ml | |
| dinner | hot chocolate (cup) | 200 | 250 ml | |
| Saturday | breakfast | oats (100 g) + honey | 440 | 325 ml |
| breakfast | coffee (cup) with sugar | 40 | 250 ml | |
| snack | trail mix (150 g) | 345 | - | |
| snack | energy bar | 235 | - | |
| lunch | cured meat, cheese, crackers | 430 | - | |
| lunch | chai tea (cup) | 105 | 250 ml | |
| snack | trail mix (150 g) | 345 | - | |
| snack | energy bar | 235 | - | |
| dinner | dehydrated risotto (170 g) | 600 | 500 ml | |
| dinner | hot chocolate (cup) | 200 | 250 ml | |
| Sunday | breakfast | oats (100 g) + honey | 440 | 325 ml |
| breakfast | coffee (cup) with sugar | 40 | 250 ml | |
| snack | trail mix (150 g) | 345 | - | |
| snack | energy bar | 235 | - | |
| lunch | ramen noodles (80 g) | 370 | 325 ml | |
| lunch | chai tea (cup) | 105 | 250 ml | |
| 3.4 l |
A one-person meal plan for a weekend trip where the target for daily calories is 3000. Indicated weights are for dry (uncooked) food.
The maths
To arrive at an estimate of how much fuel you’ll use, you only need to follow these three steps.
1. Multiply water boiled by boil time
Once you have a total for water boiled, you need to multiply this figure by your stove’s burn time (with seconds as a fraction of minute) to arrive at the total burn time. If your stove’s specified boil time was for 0.5 L water, you will need to multiply again by two to get this number. The final figure represents the amount of time that your stove would burn for if it was used to bring the specified amount of water to a boil. While actually on the trail, you might actually run the stove for longer if you use it to simmer or keep water hot.
2. Divide total boil time by your stove’s burn time
In step two, you divide your total boil time by your stove’s burn time (specified for a canister of a certain size) to get a percentage. If your total boil time is in minutes and seconds, you will first need to convert the seconds into a fraction of a minute. This final figure could end up being higher than 100% if you need more than one canister.
3. Use that percentage to calculate how much fuel you need
For the final step, multiply the size of the canister specified in your stove’s burn time by the percentage you arrived at in step three. This will give you the projected total of your fuel needs (under ideal conditions) in grams. My recommendation is to round this up to the canister closest in size. For example, if your final calculator gives you 75 grams, carry a full 100 gram canister. If conditions are far from favourable, you will need to factor this in too. A combination of wind, low temps and high elevation can require you to multiply your fuel needs by as much as 300%. I get into this in more detail in the next section.
Top tip: Many backpackers are unwilling to pack a half-empty canister (most of the weight is in the canister and not the fuel). So what do you do with those partially-used canisters? One solution is to use them while car camping.
Environmental factors that affect fuel efficiency
There are three environmental factors that can affect fuel economy and need to be taken into account when calculating your fuel needs. If you expect to contend with only one of these, wind for example, you might need to only double your expected fuel consumption, but if you expect a combination of performance-impacting factors, you might need to triple your projected fuel needs.
Wind
Of the three environmental factors listed here, wind is the one most likely to affect your stove’s performance and fuel economy. Stoves with exposed burners can use up to three times more fuel in a breeze, while stove systems like the JetBoil Flash and MiniMo fare much better in the same conditions. Given these differences in windy-condition performance, it’s not possible to make generalisations about how much more fuel you should carry if you expect wind. You’ll need to figure out how badly your stove is affected by wind and then factor that in. For example, I’ve learned to carry an additional 40% for my MiniMo when I expect windy conditions.
Air temperature
Ambient air temperature can affect a stove’s fuel economy in two ways. Firstly, if the air is cold, it’s very likely that your collected water will be too. It takes longer to bring cold water to a boil than it does warmer water, meaning that you have to run the stove for longer and use more fuel. Secondly, colder temps can cause the pressure inside a fuel canister to drop, which in turn results in a weaker flame and less-than-ideal fuel economy. This is why alpine climbers and other winter adventurers go to lengths to keep fuel canisters warm and often use inverted canister stoves. Liquid fuel stoves don’t suffer from the same low-pressure problem and are also a good cold-condition option.
Elevation
The boiling point of water varies according to elevation and atmospheric pressure. The higher you go, the lower the air pressure and the lower the boiling point of water. In other words, water boils faster at higher elevations if all other factors are constant. Of course, in the real world, elevation usually comes with colder temps and impaired stove performance (if you’re using an upright canister stove) which offsets any gains. Another factor to take into account is that raw food takes longer to cook at higher elevations. This won’t be an issue if your meals are freeze-dried or dehydrated, but if you’re planning on cooking raw noodles or rice, you’ll need to account for the extra cooking time (up to twice as long above 10 000 feet).
Activities that contribute to fuel consumption
There are two other factors, which although not directly related to stove performance, can have a significant impact on the amount of fuel you use.
Water purification
There are several ways to purify or filter water out on the trail. One popular method is to boil water to kill off any bacteria. The downsides to this option are that it doesn’t remove sediment and that it uses fuel. If conserving stove fuel is a priority, it makes more sense to carry a filter, which will remove sediment and allow you to save stove fuel. Alternatively a UV purifier or water purifying drops (or tablets) will kill off any waterborne pathogens but won’t remove sediment.
Snow melting
Snow is the most common water source in the high alpine, but melting it takes additional fuel. Unfortunately, there’s little you can do to conserve fuel here. You could collect water from glacial streams, but when the water is that cold, it takes almost as much time to boil it as it does to melt snow and then bring the water to a boil. In very cold environments, you simply have to factor in the extra fuel needed.
Tips for saving fuel
Regardless of where you’re going and the conditions you expect to face, there are a few things you can do to improve your stove’s fuel economy.
Boil only as much water as you need for a meal or hot drink
If you only need 250 ml of hot water for a cup of tea, boil only 250 ml of water. If you filled or even just half filled your pot, you would waste fuel by boiling water that would chill and then have to be reheated. Just this one fuel-saving habit can make the difference between using the amount of fuel calculated by your pre-trip projections and burning through your entire fuel supply long before the end of the trip.
Put a lid on your pot
This should be a no-brainer. As water heats up, it evaporates more quickly. The higher the rate of evaporation, the slower water boils. Keeping a lid on your pot minimises evaporation and retains most of the heat energy generated by your stove. Resist the urge to lift the lid to check if your water is boiling. You will hear the water boil or see steam escaping when it is boiling.
Run you stove slightly below full power
Many stoves burn at optimal efficiency when run slightly below full burn (around 80%). If you run your stove at maximum power, your water might boil faster, but you’ll likely waste heat around the sides of the pot. The good news for campers who like a fast boil is that the optimal power level varies from stove to stove. Integrated stove systems like those made by Jetboil actually lose very little heat when on full burn while compact canister stove are likely to be significantly less efficient when at full power.
Have meal ingredients ready before igniting the stove
To avoid running your stove when it’s not actually boiling water or cooking food, prepare all your ingredients and cookware before igniting your stove. That way, you’ll be ready to cook as soon as your stove is burning. Over the course of a longer trip these seconds can add up to minutes, which in more adverse conditions can equal a significant amount of fuel.
Keep your stove out of the wind
The most important thing you can do to improve your stove’s efficiency is shield it from the wind. How you do this will depend on the type of stove. Foil windshields work great for liquid fuel stoves and remote canister stoves, but you cannot use a wrap-around windshield with a stove that screws straight onto the top of a canister. Using a foil windshield with compact canister stoves and stove systems is very dangerous as it can cause the canister to heat up and even explode. You can, however, create an open-sided wind break using rocks to protect the flame from the wind.
In colder temps try to keep canisters warm
Fuel canisters lose pressure in colder temps, which in turn can reduce the power and fuel economy of a stove. To combat this, you need to find a way to keep your fuel canister warm when it isn’t being used. That can mean storing it in the middle of a stuffed sleeping bag or puffy jacket, putting a hand warmer under it, or even sleeping with it in your sleeping bag (wrapped in something soft).
How to calculate the amount of fuel in a canister
If you find yourself wondering how much fuel is left in a partially used canister, you can answer the question in three very simple steps:
1. Weigh an empty fuel canister
First you need to weigh an empty canister on a scale. A 100 g canister typically weighs about 95 grams when empty while a 230 g canister weighs around 125 grams.
2. Weigh your partially used canister
Next, weigh your partially used canister (the one you want to know how much fuel is left in). Obviously, it has to be the same size as the empty canister
3. Subtract the weight of the empty canister from the other
The final step is to subtract the weight of the empty canister from the partially full canister. The result is the weight of the fuel remaining in the partially full canister.
Get more advice from this gearhead
You now know how to calculate your fuel needs while also factoring in the fuel used to cook with (and not just boil water). But don’t stop here. On this website you’ll find many more in-depth gear guides on everything from tents to headlamps as well as many more how-to articles. You can find these under the different sections in the categories menu, or, better yet, sign up for my newsletter to get all the latest from Trail & Crag delivered straight to your inbox.
