What is the smallest size a full bathroom will fit?

A tub is six foot long, so if you have the tub along the end of the room, then the minimum width would be six feet. You could possibly fit in a small sink and toilet if the room is 7 foot long, but it would be tight. Also, you would have to make sure that the door would clear the toilet. Renting, or buying, people do not want the smallest possible bathroom.