It’s day five of my seven day trip. I still have a couple of days of cooking left to do. If I run out of gas, I’ll be eating uncooked freeze dried meals (yuck!). Can I afford to make my morning coffee? Just how much stinkin’ gas do I have left!?

Ever been there? Herein follows a simple, field practical way to estimate how much gas you have left in your canister:

Before you go out, take a full canister and an empty canister, both the same size and brand. Put the full canister in a container of water. Mark where the water line is.

Notice how the “P” in “Power” is just about fully submerged.

Now, take the full canister out of the pot and put the empty canister in. Mark where the water line is.

Notice how the water line now falls far down on the “tail” of the “P” in “Power”.

Then put the two canisters side by side.

Last, copy the mark from the empty canister on to the full canister. You now have a full canister with one mark where the waterline will fall when the canister is full and one mark where the waterline will fall when the canister is empty.

Now, when you’re out in the field, you can float your canister in water. The waterline will fall somewhere in between the two marks, and, like a standard fuel gauge in a car, will give you a rough idea of how much fuel you’ve got left.  Of course, there’s always going to be an air bubble underneath the concave bottom of the canister.  Do what you can to minimize the bubble, but the most important thing is consistency.  One needs to place the canister in the water the same way each time in order for the “gauge” to work.

Below is an example with a partially used canister.  It’s a little hard to tell from the photo, but  the water line on this canister appears to be slightly closer to the empty mark than the full mark; it’s just over half empty.

Remember to be conservative! Often you can’t get every last drop of fuel out of a canister, especially if the canister temperature (not the air temperature) drops below about 40F/5C, so leave a margin for error.

Having a way to gauge how much gas you have left in your canister in no way replaces planning ahead how much gas you’ll need. The “gauge” only serves to let you know whether or not you’re on track. If you wind up using more gas than expected, the gauge will let you know so you can start scrimping a bit so you won’t run out of gas.

Well, enough about fuel and stuff.  Now, get on out there and have some fun, would ya?


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