How much does a 2 1/2 square of graham crackers weigh
It would help if you provide the recipe.  Generally, there are two treatments for graham cracker in baking/cooking: layering or crushing.

If this is a recipe where the crackers are layered, it certainly won't matter, as you can estimate.

If you need to crush them, you might need to be more precise.  I can't provide the weight, but I think I can offer another way to consider the problem.

I am assuming (perhaps erroneously, but it probably wouldn't matter all that much) that the thickness has not changed.

Thanks to @Chris H for correcting my first attempt (is there a way to change this answer to his? I'm happy to hand it off...)

8 dozen 2.5 inch cookies = 600 square inches

8 dozen 2.25 inch cookies = 486 square inches

You will need about 25% more, or another 22 of the smaller cookie.

I think that should get you in the ballpark.