A 10 x 10 storage unit is equivalent in size to half of a one-car garage.
It fits the contents of an entire family room or two full bedrooms, including several small to medium-sized boxes.

A 10 x 20 storage unit is the size of a standard one-car garage.
It fits the contents of a multi-bedroom house, including several oversized items like a couch, a refrigerator, a washer/dryer and a dining room set or several large boxes.