There’s no hard reason you need to know beforehand. These questions come up all the time. You have to be able to tolerate the uncertainty until move-in day. This week, go to your local Bed, Bath, & Beyond and open a pack and ship account. Pick out what you THINK you will need. You don’t pay for it until you get to the Ann Arbor store.
On move-in day, go to your dorm and assess the room and the storage space. Then go the BBB in Ann Arbor, on Washtenaw Avenue, and pick up your BBB packages. Before leaving the store, remove from the boxes the things you now see you won’t need, and add items you now realize you will need. Check out and pay. Set up room. Go back to BBB to return items you ended up not needing or to buy additional items. Rinse and repeat. The path from the university to BBB is well worn on those first few days.