Hill Classifications

In what context are you asking? Not sure I've ever seen off road hills classified, only climbs on road. That said, take a look here:

http://www.triathlonphil.com/category-climbs-in-...

Category 4 – the lowest category, climbs of 200-500 feet (70-150m). Length usually less that 2 miles (3km)

Category 3 – climbs of 500-1600 feet (150-500m). Between 2 and 3 miles (3km and 4.5km) in length.

Category 2 – climbs of 1600-2700 feet (500-800m). Between 3 and 6 miles (4.5km and 10km) in length.

Category 1 - climbs of 2700-5000 feet (800-1500m). Between 6 and 12 miles (10km and 20km) in length.

Hors (literally ‘out’ or ‘above’) Category – the hardest, climbs of 5000+ feet (1500m+). Usually more than 12 miles (20km) in length.