How many meals can you expect to get out of the small 4 oz. IsoPro cannisters (for a Pocket Rocket)? Simple boil and eat.
I have found it takes, under ideal conditions, 1/4 oz. from the canister to boil 2 cups of water with a Pocket Rocket.
The small canister has a net weight of 3.5 oz, so that would be 14 boils. In the field, give yourself some leaway and assume maybe 10- 12.
I find if you shake it you can feel the liquid sloshing which give a rough measure of how much is left.
I find the big canister lasts me 2 weeks, 2 meals a day with a bit left over.
You might want to test it a home so you don't run out unexpectedly.