A 10x20 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.
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A 15x15 storage unit is a little larger than a one-car garage.
It fits the contents of a fully furnished 3 bedroom house, including oversized items such as a couch, mattress sets, a dresser, a refrigerator, a washer/dryer, a dining room set, an entertainment center and several large boxes.