Formula for normal attack damage calculation in League of Legends

Question

Which is the formula to calculate the normal damage in League of Legends? Is the same formula for all champions?

How much damage my champion will do with the numbers in the example?

Answer 1

Here's a FAQ that includes the damage calculation stuff from the official Forum.

Just a few pointers, before you dive into it:

• There are three types of damage: Physical, Magic, and True. Physical and Magic are pretty clear, some abilities can deal true damage.
• All damage types are treated separately.
• The calculation is the same for all champions, but depends on the hitting champ and the one who was hit. However, each champion has different base values for armor/MR/damage/etc and different increments on level ups.
• The actual damage resulting from Phys/Mag damage depends on multiple things:
  • the damage you currently dish out (what you see in your character info). This is made up as a simple sum of your base damage and any flat bonuses from items.
  • your armor/MR reduction rate.
  • your armor/magic penetration rate. These come in absolute values and percentages.
  • your enemy's armor or magic resistance.

If you haven't run away yet, then check out this guide for mathcrafting LoL.

Answer 2

There are two things that cause the actual damage to differ from the champion's displayed attack power.

First -- if the attack is a crit, it deals 200% damage (or 250% with the item Infinity Edge)

Second -- all champions have an armor value that reduces incoming damage by a percentage. This and This are good topics to browse to further understand the topic. Armor Penetration items means you are effectively fighting a champion with lower armor, and thus will deal more damage.

Finally -- each champion can have different values for their starting attack stat, and additionally gains more damage when they level. This is why two champions with the same items have different attack damage.