Here is what I do..
If I want 4- 4.5 x 6.5 mats
1. I cut the 12 x 12 sheet down to 11 x 11
2. put the edge of the sheet to measure 4.5... cut down to 6.5
3. turn the page 1/4.. edge of sheet to 4.5... cut down to 6.5 (this will cut one mat.
4. turn the page 1/4 again... measure to 4.5... cut down to 6.5
you will have 4 mats and one small little box...
For 4.25 x 6.25 mats... do the same thing but cut the 12 x 12 paper down to 10.5 x 10.5 to start..
This is just how I do it.. it eliminated me having the pinwheel shape and I could use those strips for borders and such later..
Hope that helps..even though it's much later than you probably needed the info...