How many graham cracker squares yield a cup of crumbs? Or how many rectangles (2 squares to a rectangle)?

It's going to depend some on how they're ground- for my crumb crust recipe, which calls for 1 1/4c. crumbs, I use 10 crackers.

one substitution chart I have shows 1.5 cups graham cracker crumbs = 375g. That's about 13 oz, so for one cup use about 9 oz. (I'm not sure how many crackers, but look at your box label and use appropriate amount. E.g., if box is lb, use about half a box.)