That's where engineering comes in. Need to know what material (to know the properties). Need to know the speed of the airplane (or whatever factor is used in windshield design - to know the load). Need to know the supporting geometry, attachment method (adhesive, rivets, screws, hole spacing, hole size, edge distance, etc.). Need to know windshield geometry - wrap it into a curve will be a LOT stiffer than a flat plate... So this is where the answer gets complicated.