Question: what size is a jelly roll pan?
Answer: A jelly-roll pan (either 15 ½ by 10 ½ inches or 18 by 12 a.k.a. a half-sheet pan) has 1-inch-high sides and is perfect for making cake rolls; it can stand in for a cookie sheet in a pinch. It's also a terrific roasting pan for veggies and more.