Flat armor penetration's been changed to Lethality. They're pretty much the same thing, but the bulk of Lethality's penetration scales with your opponent's level. This makes it less snowbally, meaning we can give Assassins more of it than we could flat armor penetration!
- Riot games
Calculation 7.2 (current): penetration = lethality * (0.6 + 0.4 * level / 18)
Calculation < 7.2: penetration = (0.4 * lethality) + (((0.6 * lethality) * level)/18)
2/1/2017: Updated the calculator for 7.2 (Thanks @RuneKatashima
for pointing it out!)