Usually anywhere between 20 and 60mg.  The variation of "the machine" that I use allows for extremely direct inhalation, so my first hit seems to serve mainly to pull heat into the pipe and only gives a slight amount of vapor (possibly just residue from the heated end).  The second seems to do the trick and heat up the mesh really well, but if that doesn't quite do it, the third will; I'm always feeling the effects strongly by the third.  The fourth will get whatever's left over and will serve to top it off (if there's anything left after the third).  This method and pipe have been very successful.