A 5x5 self storage unit totals 25 square feet — comparable to a large closet.
5x10 units total 50 square feet and fit the contents of roughly one room of furniture. This includes several small to medium size boxes, mattresses, chairs, and sports equipment.
10×10 storage units total 100 square feet and can fit the contents of a 1-bedroom apartment, including a mattress, refrigerator, washer/dryer, furniture, and personal items.