How to Calculate How Much Fuel is in a Fuel Can?

Author: Tina Eckerlin

Whether or not you are an ultralight hiker, no one wants to carry extra weight for nothing.

If you are using an Isobutane fuel cannister it can be difficult to know how much fuel and how many burns you have left; which can make planning for a trip difficult.

I know how frustrating it can be trying to plan fuel consumption on longer trips, especially when you are resupplying.

Many people go stove-less for this reason and of course the added weight. But, as I have mentioned before...I require a hot cup of coffee to start my day!

I have been asked so many times by other hikers how to determine how much fuel or burns is in a cannister. I have seen people take giant cannisters on a 2 night trip because they were afraid of not having enough fuel.

The reason you cannot find a comprehensive list of how much fuel is in your can or how many burns can you can get is because the amount of fuel you will burn is based on a number of things.

Fuel Consumption Factors

• brand of fuel
• type of fuel (summer or winter)
• your specific stove efficiency
• temperature
• wind
• quantity &/or length required to cook or boil
• altitude

It will take less fuel to bring 1 cup of water to a boil when it is 20 °C  than 3 cups of water at -5 °C

So, here is a list of 4 ways to calculate your Isobutane fuel based on your specific usage. The first and second method are how most people estimate, with the third and forth way being what we consider the best and most accurate way to plan.

Method 1 - The Shake Test

While some experienced hikers can guesstimate how much fuel is left in their cans by listening while they shake, it only gives you an idea of the quantity left, not the number of burns.

This is not the most effective method, but can give you an idea how much fuel is left, i.e. half full.

For this to work, you will need an idea of how many burns a can of fuel will get you. This is not an accurate method, but rather gives an idea of how much is left.

Method 2 - The Float Test

To use the float test method, you will require a container of water, a marker, a full can, an empty can and a can that you want to measure what is left.

1. Place full can in water and mark line where it reaches the top of the water
2. Place empty can in water and mark line where it reaches the top of the water
3. Place can that you want to know how much is left in water and mark. Compare between the lines of the full and empty cans. This line will tell you roughly how much fuel is left in the can.

Similar to the shake test, this method is only an estimate and does not accurately tell you how many burns left in the can, only roughly how full the can is.

Method 3 - Marking Number of Burns

This method  requires you take notes or to make a mark after each burn. 

1. Cook as usual
2. Make a mark on can or in notebook
3. Once can is empty, count how many burns that can produced under typical use

Once the can is empty, you may see that you produced 14 burns from that can from your average use. This can be used for future planning.

Method 4 - Weigh & Calculate

Weighing and calculating your fuel can give you a better idea of exactly how much is actually left in the can.

1. Weigh a full can and an empty can, take note of the weights
2. Then, subtract the weight of the empty can from the full can. This number is the total fuel weight of full can (fuel only)
3. Weigh a full can after one single average burn and take note of the weight
4. Subtract the full can weight (can and fuel) from the single average burn can weight (can and fuel). This number is the total grams of fuel used for one single burn.
5. Now divide the total full can fuel weight (fuel only) by the total single average burn fuel weight (fuel used only). This will be how many burns you can get out of the can.

Calculation example:

A. Full Can Weight (can & fuel): 213 g
B. Empty Can Weight (can only): 102 g
C. Single Average Burn Weight Full Can (can & fuel): 205 g
D. Total Fuel Weight of Full Can (fuel only): 109 g
E. Single Average Burn Fuel Weight (fuel only): 8 g
F. Total Number of Burns in can: 13.62 burns

1. A 213 g - B 102 g = D 109 g 
2. A 213 g - C 205 g = E 8 g
3. D 109 g ÷ E  8 g = F 13.62 burns

Personally,  I use Method 4 along with Method 3 to give real world statistics. I calculate my fuel, and mark number of burns directly on the can. This determines for example, If I  get 13 burns from one can with average conditions boiling 2.5 cups of water, I can decide how many burns per day I want . So if I plan 3 burns a day, then I know 13.62 total burns divided by 3 burns per day equals 4.54 days worth of fuel in a full can.

Using both of these methods I can also take a partially used can for a short trip and be confident that I still have approximately 7 burns left in the can.

Alcohol Stoves

We love alcohol stoves . They don't have parts to break, they are quiet and so easy to calculate how much fuel to bring. They also can burn different types of fuel, which makes resupplying much easier.

1. Measure fuel and place into alcohol stove
2. Test boil in average conditions
3. The quantity of fuel used to burn is the total amount of fuel required

If it takes you 1 ounce for an average boil, just multiply that by how many boils you need.

Example: 

If it takes 1 ounce and you want to boil seven times, then multiple the quantity of fuel (1 oz) by the number of boils (7). 

You will need 7 ounces of fuel.

Tips for Reducing Fuel Consumption

• Use a windscreen, windbreak or even a sit pad to block the wind
• If it is cold, sleep with your fuel can inside your sleeping bag or keep in pocket close to body
• Choose the right fuel and stove for your temperature conditions. Most fuel brands offer summer and winter fuels
• Use a wide bottomed pot with a well-fitting lid. Tall and narrow style pots are less efficient because the flame has less surface area to heat
• Only ignite fuel once you are ready to start cooking. Have everything else ready to go
• Turn off flame as soon as required temperature is achieved
• Use the optimal amount of water for requirements. Don't boil 2 cups if you only need 1 cup!
• Clean burner as needed to prevent carbon build up to maximize efficiency

Do you have any great tips on how to maximize or calculate fuel?

Let us know in the comments below!