Not much. About 18" from the base of the 3rd row to the tailgate. The seats are about 18'-20" tall from the cargo floor to the top of the seat (not including the headrests). From the top of the seats to where the tailgate window would be in the closed position is about 10". Practically speaking, I can fit two 23" roller bags on the bottom followed by two medium sized duffel bags on top of those. On top of that, maybe two computer bags and purses. Technically, with the 3rd row up, you have 10.9 cubic feet of cargo space.
2011 Q7 TDI Prestige
2013 Jeep Wrangler Rubicon Unlimited
2007 Q7 4.2 Premium-traded
2011 Subaru Outback 2.5i Limited- Sold
1997 MB S500-gone
1995 Porsche 993-gone but not forgotten