It depends on the speaker in front. Everywhere says that in front it is 6.5, but when i went to install my alpine type-r component 6.5s, it was a total b***h. You have to cut the plastic thing and make a custom spacer, unless you want to cut at your door. So make sure you do your homework on the EXACT dimensions of the front speaker you would like to use.

As for the rear its a 6.5 on the coupe and a 6x9 i believe on the sedan, there should be plenty of room to make any speaker of the right size to fit with only minor modifications.