As a rule of thumb, a 5x5 will fit one piece of furniture or several boxes, a 5x10 will fit the contents of a 1-bedroom apartment, a 10x10 will fit the contents of a small home, a 10x15 will fit the contents of a 2-3 bedroom home, a 10x20 will fit the contents of a 4 bedroom home, and a 20x20 will fit a lot more.