10' x 10' storage units tend to be the most popular. They offer 100 sq feet of storage, which is equivalent to a single bedroom. This can usually accommodate enough storage for two average sized rooms.

A 10' x 10' storage unit can be used to store most items from a 2 bedroom house. It is able to accommodate appliances, mattresses, furniture and smaller items from your 2 bedroom house. If you're also including garage items you may want to consider a 10' x 20' unit. 

For a 3 bedroom house, a 10' x 15' foot (150 sq ft) or 10' x 20' (200 sq ft), should be able to fit most belongings. These unit sizes are equivalent to a garage, with ample space for large appliances, mattresses, furniture, electronics, and tools.

When storing a TV or electronics, a heated or climate controlled storage unit is best. Keeping electronics at a constant temperature is most important when storing long term, as swings in temperature will cause moisture to form.