the rear are 6x9, but shallow. The 02s I believe count the tweeter in the 6x9 as a seperate speaker. The front are 6 3/4 but a 6 1/2 will work. There are plenty of people who have stated what the replaced their speakers with, so check out the archives. I put the JL Audio XR650cs upfront and some Kenwoods in the back. With a couple JL subs and a 5 channel amp, it sounds awesome. I did have to put in a 1 farad cap and Optima yellow top though, as I run all my lights most of the time at night.