"As others have pointed out, putting something like paper inside is a good idea to keep it straight and structural. Otherwise, you may have a rather floppy experience. I ordered the medium, and as the owner of a very normally proportioned head, I can confirm the fit was snug, but comfortable.
It is difficult to describe just how huge this hat is. Pictures do not do it justice. If you wear it, you will hit every door frame, and you will get stuck on things you cannot see. It is ridiculous, it is impractical, and it is, perhaps, one of the worst kinds of headwear you can wear to a funeral (unless the deceased was very cool indeed). But none of that matters, because if you order a giant wizard hat, you know what you're in for. The courage to wear the hat is what separates apprentices from the real magi."
MERLIN WIZARD SORCERER Hat 28" to 30" Tall Blue Fleece and Assorted Colors Adult sizes