It's relative to the meths system you have Daniel, with the cone clone set ups i use i can boil 300ml for a cuppa with 12ml, and 500ml with as little as 18ml or so depending on conditions, i have 3 different set ups though, all home made, i've no idea how these figures match up to a commercially purchased option like the Trangia or the stuff tinny sells etc so can only go on my set up.
It's a niche thing that requires a certain amount of practice before you head out relying on it imo, other options are far easier unless you're really into lightweight long weekends at all costs, and beyond long weekends gas becomes much more user friendly imo.
Have a play at making a couple of burners and see how it goes.
Include a little history in your walks. Pecsaetan - Ancient Derbyshire, Staffordshire and South Yorkshire - http://pecsaetan.weebly.com/
Edited: 30/04/2012 at 04:29