[ghaff]

Something about that size seems like pretty much the bare minimum. My point of reference is a hotel I often stay at in NY which makes something of a virtue of its small "cabins." They're 170 sq. ft. and the minimally separated bathroom is about as small as you could make it. There's a bed and a minimal desk (maybe a few square feet) and desk chair. No closet, no kitchen or even room for a mini-refrigerator or hotplate, etc. Add 80 sq. ft., make the bed a futon, and you start to be a place where one person could almost live out of a suitcase but it would still be pretty minimal for any length of time.