I've always floated them in water to see how much is left. Now they print the process on the MSR cans (what I use)
I never take a half gone can on a trip unless it's an overnighter. I use my partials in the Jetboil to make coffee in the truck. I also have a lantern that burns them. It comes in real handy at bow shoots, and fishing trips around camp.
Like somebody else said, I always burn a new canister at least once.
I like the weight idea though, I'll give it a shot.
