It's very much system dependent.
- Are you doing a full wort boil? I assume so.
- What is your evaporation loss (determine empirically)?
- What are your system losses, i.e., deadspace in kettle, cfc chiller losses, hose losses?
- Whole hops? They will absorb some wort, probably around .25-.5 pint per ounce (I think, can't remember off the top of my head).
Your final target volume (5 or 5.5 gallons) plus all of your losses equal your starting boil volume.