## Tuesday, December 20, 2016

### Calculating the Fuel Needed for a Trip

Here's an example of how I calculate the amount of fuel needed for a given trip.  You should be able to do something along these lines and come up with a number that will work for you.

 Planning for a trip in the back country?  Sounds fantastic. Um, how much fuel are you going to need for that?
First, I write down when and how much I'm going to boil throughout each day.  For example, look at the chart below.  I typically boil two cups (about 500 ml) of water per meal for breakfast and supper. Maybe I'll boil a little less for breakfast.  I typically have a cold lunch.  I also like to have a cup of coffee or tea in the morning, and then a cup of cocoa or tea in the evening, which means I'll boil another two cups per day for hot drinks.  I typically use cold water for cleaning up after supper, so no fuel consumption there.

Given all of the above, I'm going to boil about 1500 ml per day.  OBVIOUSLY this is just an example, and I'm making everything uniform so it's easy to understand.  In real life, the amount you boil may vary from day to day depending on your menu, how much you eat, whether or not you use hot water for personal hygiene or dishwashing, etc.  This example is all about round numbers and easy to follow calculations.  The numbers are reasonable, but of course you need to adjust everything to how you cook, how often you cook, how many people you cook for, etc.

 Wow.  Looks like a beautiful spot. How many days will it take you to get there, how many meals will you eat on the way, and how much fuel do you need?
Second, I write down how much fuel it's going to take to boil each amount of water I've written down in step 1.  For most stoves, that's about 7 or 8 g per 500 ml boil although you can get by with less if you follow the rules of stove fuel efficiency.

NOTE:  If you use a Jetboil or other similar integrated canister stove or you use a heat exchanger pot, then instead of 7 to 8 g being the typical amount of fuel needed to boil 2 cups of water, you might plan on 5 to 6 g of fuel per boil.

Yes, you'll have to adjust these numbers. Again, this is just one example, using the "backpacker's standard" of 2 cups per boil, which is about what most freeze dried meals require.  As you adjust these numbers, remember that it's more efficient per cup to boil a larger quantity than a smaller.  In other words, if 2 cups requires, say, 8 g (4 g per cup), 3 cups might only require 10.5 g (3.5 g per cup), and 1 cup might require 4.5 g.  Something like that.  You need to adjust all these numbers based on your experience of how much fuel you actually use.  For this example, I'm going to choose a number of 8 g per 500 ml boiled which is neither overly generous nor overly optimistic.
 Nice spot to camp.  It'd be a shame to run out of fuel and spoil such a perfect camp.
Third, I total up the amount of fuel that I'll need for the whole trip by summing the amount needed for each day.  Many people do not cook breakfast on the first day or supper on the last; in that case you would need to adjust these calculations.  This total amount needed has to be less than the amount contained in whatever canister I intend to bring.  You should also add a "margin for error," particularly on cold weather trips.  The more experience you have, the smaller margin you can plan on.

Given the example presented in the chart, below, I need about 96 g of fuel for a four day trip or about 24 g per day.  Yes, I know we might get better actual results than 8 g per 500 ml boiled which would give me different numbers, but let's just go with 8 g per 500 ml boiled for this example.  If I need 96 g of fuel, and I take a 110 g canister of gas, I would have 14 g as a margin for error.  You'd have to think about whether or not that's going to work for you.  If the weather's warmer, then maybe that's fine.  If it's colder, maybe plan on more.  If you're with a group, maybe that's fine.  If you're going solo, maybe plan on more.  And so on.  Think it through and bring the the amount you feel comfortable with.
 East Vidette as seen from the John Muir Trail. Don't let poor planning ruin your dream hike!
While these numbers in the below chart aren't actual data from a trip, they're within the realm of reason.  Therefore, allocating 25 g of fuel per day isn't unreasonable until you get a better sense of how much your cooking actually requires.  Twenty five is a fairly easy number to work with, and the most commonly used canisters contain about 100, 200, and 450 grams of fuel. Twenty five divides easily into 100, 200, and 450.

NOTE:  For your first several trips, if you're new to backpacking, assume you'll need more fuel rather than less until you get a feel for how much fuel your style of cooking actually requires.

 Amt Boiled (ml) Fuel per boil (g) Day1 Breakfast 500 8 Supper 500 8 Hot Drinks 500 8 Day2 Breakfast 500 8 Supper 500 8 Hot Drinks 500 8 Day3 Breakfast 500 8 Supper 500 8 Hot Drinks 500 8 Day4 Breakfast 500 8 Supper 500 8 Hot Drinks 500 8 4 6000 96 Average g of fuel per day: 24

As always, I thank you for joining me,

HJ

Note:  All photos are from my 2015 John Muir Trail section hike (Onion Valley to Whitney Portal).
 The author, out on the trail where he belongs. Why on earth am I indoors blogging on stoves right now?

1. As always, thanks for all of your good information, Jim!
Mike P.

1. Hi, Mike,

I hope some of the Scouts find this helpful.

HJ

2. Good post. Do you ever weigh your fuel before and after a trip?

1. Thanks, Bill.

Yes I do sometimes weigh my canisters if
a) I have a significant amount left or
b) I'm trying to calculate fuel usage

HJ

2. I weigh them, then note the weight and date on the bottom with a marking pen .....

3. That's certainly a good way to do it.

HJ

3. Always weigh and mark canisters if I have any left. Makes it easier to use them all up. ( for short backpacks under 4 nights or car camping )

1. Hey, Sooz. :)

Yeah, that's a best practice. Even better if you log it in Excel or something. Then you know how much a certain type of trip requires. A little anal though, so I do my rough estimates based on 7 to 8 g per 2 cup boil at 65 degrees.

HJ

4. Awesome information. I was researching on methods of lightening up my backpack and I stumbled across this site. Great stuff! Did a 7 day walk on the Overland Track in Tasmania some days ago. Inside a hut near the end of the track I found a lot of new canisters abandoned there cause people can't fly home with them. I was carrying two 8 oz canisters. Now think about it one will suffice.

1. I have actually seen people carrying a 450 g canister, which is really a shame; there's just no need for it. My hope is that people will feel more confident with less -- but still enough -- because of this post.

HJ

2. Re the above, on a simple weekend trip I mean.

Obviously there are trips with either enough people or of sufficient duration where a 450 g canister is truly necessary.

But for one or two people for a weekend, there's just no way I can see needing a 450 g canister. Most people will find 110g entirely sufficient.

HJ