A 5x10 storage unit is the size of a small walk-in closet.
A 10x10 storage unit is the size of half of a standard one-car garage.
A 10x15 storage unit is a little smaller than a standard one-car garage. It fits the contents of three full bedrooms and larger items such as a piano, couches, tables, or large-screen TVs, plus several medium to large-sized boxes.
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.
It fits the contents of a fully furnished 3-5 bedroom house, including oversized items such as couches, beds, dressers, a refrigerator, a washer/dryer, a dining room set, an entertainment center, and several large boxes. You could fit a car in this size of unit.