How much is a cup of graham cracker crumbs in crackers and weight?
It should be about 7 crackers per cup, maybe 8, depending how finely you crush them. One of the inner packages from your 14.4oz box should be plenty (there are probably three packages with 9 in each, or 4.8oz). If you need to go the other way, that's 1/7 to 1/8 cup per cracker, or more simply, 0.5oz or 15g per cracker.

I know this from making graham cracker crusts - and you can confirm it by looking at some recipes. You generally need 1.5 cups of crumbs for a pie crust, and it takes 10-12 crackers. I've seen recipes ranging from 9 to 12 crackers (and checked ten or so when writing this), but I don't think I've ever used fewer than 10. One cup is 2/3 of that, 7 or 8 crackers. (Some people do say 20 or 24 squares, but they're clearly half-cracker squares, not the whole crackers.)

For what it's worth, the Martha Stewart crust recipe says "6 1/2 ounces graham crackers (12 crackers), finely ground (1 1/2 cups)", and 2/3 of that is 4 1/3 oz, pretty close to 1/3 of your box, maybe a cracker short, so by weight this works out too.