This website uses the Sierra Club's difficulty rating system:|
"A" -- More than 16 miles or more than 3,000 feet of elevation change.
"B" -- 8 to 16 miles and between 1,500 to 3,000 feet of elevation change.
"C" -- 3 to 8 miles and between 500 to 1,500 feet of elevation change.
For purposes of this website "elevation change" means elevation change in one direction, so if a hike goes up 3,000 feet, and then back down 3,000 feet, it would be classified as having a 3,000 foot elevation change.
Don't try a class A hike unless you have done a class B hike recently without suffering too much. Similarly, you should probably do a class C hike before you try a class B hike. See Hiking Tips.