Please move if not appropriate. I'd like to understand how filling my butane lighter works from a more rigorous point of view than just guessing. How I can tell when my refill cannister is getting inefficient? (i.e. more rigorously than just shaking it or weighing it) I hope to detemine how full a random refill is by observing its buoyancy compared to a full and an empty cannister. So - the ideal goal is to fill the lighter as full as possible with liquid butane. When I put a butane refill, it is liquid butane under pressure. When I fill the lighter, it will equalize pressure. Is liquid butane compressible? As the refill loses liquid, the pressure will drop. Does the butane start to evaporate? Ultimately, I hope to establish a function relating amount of refill left (in grams) to effficiency of lighter filling. As is apparent by the scattered nature of my comments and questions, I'm discovering it to be a lot more complex than I thought at first.