A question about Armor/Magic Penetration.

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Rotterdammer

Senior Member

30-06-2010

Hi guys !!

I have a lil question

So when I have armor or magic penetratiton I do more damage ? or I do more damage if that person gots armor or magic defans items ??

Can someone explain it to me

I dont know why but Im always buying last whisperer with shaco :P


A example : last whisperer gives +10 attack +40 attack speed and +40% PASSIVE armor penetratiton if I got 2x last whisperer will it be +80% or because its passive you can only use 1 of the same item and it will stay at +40% ?


Thank you !


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Ahri Nine Tails

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Senior Member

30-06-2010

Surely that should be extremely obvious. I'll explain some rough points as I'm a bit unknowledgable when it comes to the maths

-Armor pen makes you do increased damage by ignoring x amount of the enemies Armor value

-Magic pen is the same as Armor pen except that it ignore Magic Resist instead

-Higher armor or magic resist means you take less damage. Ingame you can scroll over your Armor and Magic Resist values to see how much you actually resist. Note that these won't take into account enemy armor and magic penetration.

-If an item such as last whisper says UNIQUE on it, it means that anything written after UNIQUE will not stack if you buy multiple items. If you buy 2 last whispers, you'll get...

+20 attack
+80% attack speed
UNIQUE PASSIVE: 40% armor penetration


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Acceleratum

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Member

30-06-2010

The passive is unique so u only get 40%

And yes, you do more damage if you have more penetration... but dont mix normal penetration with percentage penetration, either get last whisper only, or lots of the other armor penetration items.


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Taupe

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Senior Member

30-06-2010

Armor reduces incoming physical damage.
Magic Resistance reduces incoming magical damage.
So if your opponent has a lot of armor your auto-attacks (or some skills) will do less damage.
If you have armor pen, a part of that armor will be ignored.
Let's say the enemy has 100 armor, if you have last whisper you have 40% armor pen, so it is like your enemy has only 60 armor.

the formula goes: damage = (damage before reduction * 100) / (100 + enemy armor)

edit: ahhh i'm writing too slow


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Rotterdammer

Senior Member

30-06-2010

Thanks for the info guys <3


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Wildchampion

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Member

30-06-2010

Just a small question about armor pen and magic pen let say a target has 100 magic resist and i have mastery for 15% magic pen + void staff 40% magic pen and some runes for let say another 10 magic pen, so i would reduce the magic resist by 55% (55) + 10 = 65? Or does it work somehow diffrently?


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Project Insanity

Senior Member

12-07-2010

Penetration as a number and penetration as a %age are different,

In that situation, (I'm not sure which order it goes in, but I think this is cortrect), if an enemy has, say, 110 magic resist, the flat 10 would come off first, making it 100, then the %age would come off, making it 45.


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PrincessKay

Senior Member

12-07-2010

Quote:
Originally Posted by Project Insanity View Post
Penetration as a number and penetration as a %age are different,

In that situation, (I'm not sure which order it goes in, but I think this is cortrect), if an enemy has, say, 110 magic resist, the flat 10 would come off first, making it 100, then the %age would come off, making it 45.
You are correct, Project Insanity.

Magic Resistance is affected as follows:

-Flat MR reduction - eg. Abyssal Scepter and Fiddlesticks passive

-Percentage MR reduction - currently only on Nidalee's Bushwhack ability - thanks to skyqula for adding this.

-Flat Magic Penetration - eg. Sorcerer's Shoes

-Percentage Magic Penetration - eg. Void Staff


Armour is affected the same:

-Flat Armour Reduction - eg. Stark's Fervor - thanks to Bibidiboo for pointing this out. For some reason it completely slipped my mind.

-Percentage Armour reduction - currently only on Nidalee's Bushwhack ability - thanks to skyqula for adding this.

-Flat Armour Penetration - eg. The Brutalizer

-Percentage Armour Penetration - eg. Last Whisper


Note that the final stage, Pecentage Penetration, for both of these applies multiplicatively.
Meaning that if you hold a Void Staff and have the Archaic Knowledge mastery you will only actually get 49%, total, percentage penatration not 55%


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EvilToast

Junior Member

12-07-2010

Quote:
Originally Posted by PrincessKay View Post

Note that the final stage, Pecentage Penetration, for both of these applies multiplicatively.
Meaning that if you hold a Void Staff and have the Archaic Knowledge mastery you will only actually get 49%, total, percentage penatration not 55%

i don't get this calculation^^
archaic knowledge gives 15% magic armor penetration
void staff gives 40 % magic armor penetration

though u get void staff AFTER the mastery, do you, in total, get 15 % + (15*40%) magic armor penetration? this would equal 21 %. oO
now i am confused xD


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PrincessKay

Senior Member

12-07-2010

Quote:
Originally Posted by EvilToast View Post
i don't get this calculation^^
archaic knowledge gives 15% magic armor penetration
void staff gives 40 % magic armor penetration

though u get void staff AFTER the mastery, do you, in total, get 15 % + (15*40%) magic armor penetration? this would equal 21 %. oO
now i am confused xD
Actually, you're thinking about it the wrong way round.

NOTE: I'm probably not the best person to explain this; if you can follow this then you could probably explain it back to me even better.

I think it works in an almost reverse order:
15% penetration = Hitting against 85% of their MR/Armour(note: there are currently no other percentage armour things).
40% penetration = Hitting against 60% of their MR.

85%*60% = 51%

Therefore you are hitting against 51% of their MR/Armour and therefore only penetrating 49%.

I quoted the result from here and after playing with the numbers that was the only, logical, sense I could make of it.

If somebody else with a better understanding of mathematics could help prove me right/wrong then it would be most appreciated.


EDIT: It may also be worth adding, in order to keep all the info in one thread, that by using items like Abyssal Scepter and Black Cleaver it is possible to reduce your targets MR/Armour to Negative values, however, Magic/Armour Penetration only applies to MR/Armour that is Positive.

In sum: Increasing your MR/Armour reduction will not benefit your Armour/Magic Penetration, in fact quite the opposite, it will weaken it's affect.


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