A 10x10 contains plenty of space to hold the contents of a typical one bedroom apartment. One hundred square feet allows for plenty of space for two full rooms of furniture including sofas, bedroom furniture, kitchen appliances, and much more. You will probably even have room for extra boxes of clothing, kitchen items, seasonal items, or office records. 

 200 square feet of space provides room enough for a moderate sized house with typical furniture. This large unit can store multiple large furniture items like refrigerators, living room furniture, washers, dryers, and still leave room for those smaller items and many large boxes. A 10x20 is also large enough to store most vehicles if the storage facility allows.

 A 10x30 unit provides plenty of space for 5-7 rooms of furniture or office equipment. It is also a great sized unit to store a vehicle while leaving plenty of space around the vehicle to store additional items such as boxes, bicycles, or smaller furniture items.