Avalanche Sizes
Avalanche sizes are classified by destructive potential. They range from size one, which are fairly small, to size five, which are the largest known slides.
Size 1
Size 1 avalanches are relatively harmless to people, except that they could push you into a more hazardous situation.
Avalanche Canada 
Size 2
Size 2 avalanches are big enough to bury, injure or kill a person.
Avalanche Canada 
Size 3
A size 3 avalanche could bury and destroy a car, damage a truck, destroy a small building, or break a few trees.
Robin Siggers 
Size 4
A size 4 avalanche could destroy a railway car, large truck, several buildings, or a forest area up to four hectares (~10 acres).
CMH 
Size 5
A size 5 avalanche could destroy a village or a forest of 40 hectares (~100 acres). The avalanche pictured destroyed more than 20 hectares of forest and had a crown up to eight metres high.
Ruedi Beglinger/Selkirk Mountain Experience