Hey Jen and welcome to planDisney. I am glad you asked this question because I have seen Guests with super huge backpacks and teeny-tiny backpacks all be able to navigate a 12-15 hour day in the theme parks with ease. For me, I am a minimalist and like to travel with the least amount of items weighing me down.
According to the
Walt Disney World Resort Property Rules, you are allowed "suitcases, bags, coolers or backpacks, with or without wheels," no larger than 24" long x 15" wide x 18" high (61 cm x 38 cm x 46 cm). But what exactly are those measurements with regards to a backpack? In your case consider the 20" top to bottom measurement as the 24" long side. If the other dimensions of your specific bag fall within the other measurements then you should be ok with your current backpack. That being said there is some bag subjectivity when passing through security so you may want to consider a small backpack if you have one. Remember, you will be carrying this all day long and trying to get it to fit into attraction vehicles or
Rental Lockers.
Jen, I hope this helps you as you plan for your next great Disney adventure. Please feel free to
write me back directly with any follow-up questions or for other Disney vacation planning tips.
Enjoy making many Magical Memories.
~Jason