front- 4"
back seats - 3.5"
hatch area - 5", yep 5". You can drop 4" in there or use a dremel on the speaker box to make 5.25" work. I just did that. Requires a fair amount of dremelling, but I got Infinity 5.25" to fit flush in the speaker box. Whatever speaker you use, it can't have a depth any greater than the Infinity (forgot what the depth of the Infinity is)