Here's the power ranking for humans, elfs, demons and other races.
Bronze : Level 1 - 10
Iron : Level 10 - 20
Silver : Level 20 - 40
Gold : Level 40 - 60
Emerald : Level 60 - 100
Platinum : Level 100 - 150
Mithril : Level 150 - 300
Obsidian : Level 300 - 500
Orichalum : Level 500 - 1000
Adamantite : Level 1000 - 2000
Black Knight : Level 2000 - 3000
Earth Knight : Level 3000 - 4000
Shadow Knight : Level 4000 - 5000
Heavenly Knight : Level 5000 - 7000
Sage Knight : Level 7000 - 10.000