My hallway is 4 feet wide. What's the narrowest and widest runner area rug widths that are appropriate for this space?

I would guess that you wouldn't want anything wider than 36" or narrower than 24".

36 is preferable, nothing more narrow than 30.If you are having it cut to size, take the same measurement off the ends, so the exposed wood is the same on all four sides.

Charles - Thanks. I appreciate your feedback. Naturally my favorite rug is only 24".

Graciepj - Thank you as well. I am going to average your answers and take my changes with my favorite 2' choice.

2.5 to 3 feet should do it for you. There must be enough room for you to walk around but the hardwood should be visible as well. If you still can't decide then you can try out a few samples of various sizes before actually making uo your mind.