The National Study Group on Compulsive Disorganization created a Clutter Hoarding Scale in 1993 as a guideline for professional organizers making their first contacts with clients.
The references below only pertain to the clutter aspects of hoarding.

LEVEL ONE:
No excessive clutter
All rooms being used for intended purposes
Consistent routine housekeeping and maintenance

LEVEL TWO:
Clutter obstructs some functions of key living areas
Slight congestion of exits, entrances, hallways & stairs

LEVEL THREE:
Clutter obstructing functions of key living areas
Clutter exists around exits, entrances, hallways and stairs
At least one room not being used for intended purpose

LEVEL FOUR:
Diminished use of and accessibility to key living areas
Several rooms cluttered to extent they cannot be used for intended purposes
Clutter inhibits access to exits, entrances, hallways and stairs

LEVEL FIVE:
Key living spaces not usable
All rooms not used for intended purposes
Exits, entrances, hallways and stairs blocked.