Backspacing....I need some help...

I am trying to figure out what backspacing I need to have with a wheel thats 22x9. Its goin on a 2001 ext. cab F150. Before I order my wheels today I am tryin to get a solid answer....I have had a few friends tell me 4 or 5 different things. The truck is bagged right now on stock wheels.

look in the baggin an expedition thread, i think its mentioned in there.

I read throught that thread and didnt see anything that helped me. I am really stumped on this....anyone out there with a solid answer???