If you want to know what size mat you need, go to the accuquilt site, locate your die and there's a bunch of info provided including which machines it works in and the size cutting mat you need.
http://www.accuquilt.com/go-shop/die...are-6-1-2.html
According to the site, you need a 10X10 mat to cut the 6.5" square die. Same with the strip cutters, find the one you want on the website and it will tell you what size mat.
Have fun!!!!