If you are using whole sheets of graham crackers, you'll need about 15 sheets. Pulse to grind them in your food processor until you have 2 1/2 cups graham cracker crumbs. If you want to purchase graham cracker crumbs, that's fine too. It's unlikely you'll find cinnamon graham cracker crumbs in the boxed variety, so I recommend adding 3-4 tablespoons granulated sugar + 1/8-1/4 tsp ground cinnamon to your store bought crumbs, and then add the butter.