A 5x10 unit is approximately the size of a walk-in closet. It will hold the contents of one mid-size room or 20 large boxes

A 10x10 unit will hold the contents of three rooms:  bedroom set, living room, kitchen

A 10x20 unit is approximately the size of a one car garage. It will hold the contents of a house: appliances, dining room set, bedroom sets, large boxes