According to the "Related Questions" below, one source says 6x8, but 2 others indicate 6 1/2" rounds.
A very reliable source is Crutchfield.com - click on "outfit my car" from their home page.
My money is on 6 1/2 also...
6 1/2
Front 6X8 Rear 6.5
5x7
Listed on the driver's door post.
4 " x 6" speaker
6x8
215/60-16 Listed on the driver's door post.
On a 2004 Ford Taurus : Open the drivers door and on the latch pillar you will see an information sticker . One of the things it shows is the original size of tires on the vehicle from the factory
5 1/4 inch, or 13cm
front speakers are located in the door panels. the size is 6x8 or 5x7
door speakers are a 6 1/2, and rear speakers are 6x8
5x7's, which is the same as 6x8's...