Yeah, I know! I just got my housing packet today too! But this is what the "Welcome" brochure says (you probably got it too):
"The bed size for Mercer and McMahon is 33 x 78 inches. The bed size for Hansee, McCarty, Haggett, McMahon, Stevens Court, Terry, and Lander is 36 x 78 inches. Twin-sized fitted sheets will provide a tight but reasonable fit. Most students choose to purchase extra-long sheets, which provide a looser fit and are a bit easier to put on."
So I guess XL sheets are recommended, but not necessary?