i beleive the doors are 5.5" and the rears are 4" i put 6.5" in both.. front was easy.. rears.. not so much, there was very very little material left of the speaker mounts, people have done 6x9s back there... but not easily at all, if you are doing a serious system its probably fine to just do 5.5" or 6.5" in the rears and let your subs handle the bass