Speaker size in the rear!

I have four speakers in the rear of my 97 grand prix. I can't fiind the size of the smaller size speaker. Are they 3 1/2" or are they 4" im not really sure. I been looking all over the web and can't find the size.

Try this: http://www.crutchfield.com/S-cjr75vhAXPx/cgi-bin/ProdGroup.asp?g=400

According to this site they are 4 inch!