If you're starting out with full-sheet graham crackers, you can use a food processor or blender to grind them up. Or crush them in a zipped top bag with a rolling pin.
Mix the graham cracker crumbs, melted butter, and granulated sugar together with a rubber spatula in a medium bowl until combined. The mixture will be thick, coarse, and sandy. Press the mixture into the bottom of the dish or pan and slightly up the sides. This crust will fit into a 9 - 10-inch pan. Make sure it is tight and compact. Use the bottom of a flat measuring cup as I do in these photos. It helps! The crust will be thick.
For a baked dessert, pre-bake this crust per your recipe's directions. I usually pre-bake for 10 minutes at 300°F (149°C) or 7-8 minutes at 350°F (177°C). For a no-bake dessert, chill the crust for 2 hours before using it in your recipe.
Make-ahead tip: It's freezer friendly! Freeze the prepared crust in your pan for up to 3 months. Thaw before using in your recipe. For shorter storage, keep the prepared crust in the refrigerator for a few days before using it in your recipe.