It isn't a well-formed question. There's so many different kinds of buses, there might be furniture, it might be toy bus, the doors might be open, it might be an alien bus, it might be full with people or superglue; Who knows? The question is so loosely-formed as to be nonsensical. You might as well ask "How many/much object(s) can fit (insert spatial relationship here) (a/an/the) thing(s)?"