A 100g canister will last 2 people about 4.8 days using something like a Jetboil or MSR Windburner, and 2.4 days using an open stove like an Optimus Crux or MSR Pocket Rocket or similar. You just wanted an answer right? Now you should read the caveats below and make your own decision!
Caveat 1. The amount of stove fuel used varies a lot between hikers. Some people are 4 cup a day regular hot drinkers. Unbelievably, there are also hikers who don’t drink tea or coffee at all! Some people prefer to cook on their stoves and some rely solely on boiling water to rehydrate their freeze dried meals. The type of stove you use is important too. In short there is a great variance in how much fuel you will use based on your own personal needs.
Caveat 2. There are uncontrollable variables too, these can change the amount of fuel you use from trip to trip and day to day; ambient temperature, starting temperature of the water, wind, elevation, fuel quality.
A note on stove type; stove systems such as the Jetboil or MSR Windburner which have integrated wind protection and heat exchange features are far more efficient in their gas usage than open stoves such as the MSR Pocket Rocket, Optimus Crux or 360degrees Furno. You really can halve the amount of fuel required when using a Jetboil or MSR Windburner over an open stove.
Here’s how we made our calculation. Using Jetboils’ calculations (documented as a handy pictorial on the side of their canisters), they indicate how many boils (of 500ml of water) you’ll get out of each canister size (in perfect conditions, at room temperature). They suggest a 100g canister will give you 24 boils. It is simplifying things a bit, but that’s about 48 cups (250ml) of boiled water.
So, if you can calculate how many cups of water you need to boil each day you can work out how far each 100g of gas will go in a Jetboil stove, and you then can extrapolate that out to other stove types. Using Jetboils’ calculations you will get about 48 cups of boiled water out of a 100g Jetboil canister using a Jetboil stove. If you double usage for an open stove, that’s 24 cups of water boiled out of 100g. Remember those variables though – wind, temperature etc etc, they’re potentially going to increase usage and so is the size of your cup! So treat these calculations as a best case scenario and build a small buffer into your calculations.
For me and my walking buddy, we start the day with a cup of tea, rarely miss a mid morning coffee maybe even an end of day cup of tea, followed by some hot water to rehydrate dinner, and a cuppa after dinner – I know…. That’s about 10 cups of water boiled so, you guessed it, that 100g canister will last 2 people about 4.8 days using something like a Jetboil or MSR Windburner, and 2.4 days using an open stove like an Optimus Crux or MSR Pocket Rocket or similar.
What if I’m using liquid fuel?
Liquid and spirit stoves tend to use a little more fuel than canister stoves but have the advantage of offering consistent heat at both cold and warm temperatures, so it removes the weather variable that affects canister stoves. Liquid fuel also has the advantage of being able to be seen and measured so you can accurately gauge how much fuel you’re using or have left. This makes it much easier for you to calculate how much fuel you need to take based on how long your fuel takes to boil a litre of water and how many boils you need in your day.