### Armor/Magic/Pen mechanic

Kantrix

Senior Member

I dont see it mention here, though I am sure I saw a guide/explanation somewhere. But my question is a little specific, so here goes.

How exactly does the armor/magic resist and respective penetrations mechanic work?

Better yet, here is why I am asking:

Lets say I have an attack that does 200 damage (my auto/basic attack). Now lets say I somehow have the choice of using it once for the 200 damage, once per second, or twice per second at 100 damage. The DPS is the same...depending on the armor mechanic.

See, if the armor mechanic works like "reduce damage by a flat X", then the 200 damage is better. All higher single attacks will work better as they exceed the threshold more.

On the other hand, if armor is percent based, as in "reduce damage by X%", then it doesnt matter which method I use, since the total damage will be reduce the same. (There is the possible benefit of getting more proc's with higher attacks per second though, and thus the root of the question.)

So, how exactly does it work? And does the penetration mechanics work similarly?

SomniumProxy

Senior Member

Quote:
Q: How does armor and magic resistance work? (Credit to Garek for framing it better than I could.)

Every 1 armor means the damage it takes to kill you is extended by 1% of your hitpoints. At 100 armor, it takes 100% more damage to kill you, ie it requires double damage, ie you're taking half-damage. At 300 armor you're taking 25% damage, etc.

Magic resistance works in the exact same fashion, except it does so against spells only. There is no overlap between armor and magic resistance at all. (Ex. Having 500 Armor would have no impact on spells, having 500 Magic Resistance would have no impact on physical attacks)

terembura

Senior Member

Short answer: The armor/MR is percentage based, but you can check it by hovering your mouse over your armor stat on the bottom left corner of the screen.

Armor and MR calculation formula (<armor> / (100 + <armor>)
So if you have 40 armor, then the reduction is 40/140=28%
If you have 300 armor, then the reduction is 300/400=75%

Attack speed vs attack damage:
200 damage with 1 attack / sec seems the same as 100 damage with 2 attacks / sec, but it's only true if your target isn't moving. In the reality attack damage is better then an equal attack speed increase, because your target will run away/you will be slowed/you switch targets, etc... Of course there are exceptions for certain champions/abilities/situations...

Penetration:
It simply lowers your opponents armor/mr against you (but you can't lower it below 0)
So if the opponent has 40 armor and you have 20 armor penetration, then hi will reduce your damage by (40 - 20) / (100 + (40 - 20)) = 16%

Percentage based armor penetration is of course percentage based. So if you have 40% armor penetration against a target with 40 armor, then: (40 * 0.6) / (100 + (40 * 0.6)) = 19% reduction

Currently the flat penetration calculated before the percentage based penetration.

Kantrix

Senior Member

Thanks all!

OmniOmega

Senior Member

So is it more cost effective to buy Magic/Armor pen, or AP/AD?

Emissary of the League

Quote:
Originally Posted by OmniOmega
So is it more cost effective to buy Magic/Armor pen, or AP/AD?
Depends if the enemy team is buying lots of armor.
Everyone starts with some armor and mr, but thats about 30

Doctor Awesome

Senior Member

Quote:
Originally Posted by OmniOmega
So is it more cost effective to buy Magic/Armor pen, or AP/AD?
This can depend on several factors. For mages, one thing to consider is your champion's AP ratios--that is, what portion of their AP is applied to the damage of your spells. Some champions have abilities with poor AP ratios but low cooldowns, so they can use their spells rapidly, and other champions are the opposite.

Generally, if your champion has low AP ratios, penetration will be more effective, and AP will be more effective for high AP ratios, but this is not to say that you shouldn't get a bit of both.

Annie is an example of a champion with low AP ratios (most of her spells are around 50% or so.) Morgana is an example of a champion with high AP ratios (just about 100% on all of her spells.) You will notice that Annie has much lower cooldowns than Morgana, though, so it balances out.

For physical champions, you generally have to make a tradeoff: penetration is cheaper, but generally doesn't have as powerful upgrades available in equipment; damage is very expensive, but you can buy a lot of it. A player can stack Armor Penetration to its maximum, and they would be pretty powerful, but a champion similarly invested in pure damage would probably be a bit stronger (although less powerful against tanks.)

Generally, if the enemy team has multiple members who are building significant defense (i.e., more than one tank, several naturally tough DPS champions buying defense, support champion with defense buff spell), you should get some penetration. If they have one champion who's the designated tough guy, you should probably focus on raw damage and deal with the tough guy when you've handled his flimsier but more dangerous allies.

As to what kind of penetration, it again comes to the team makeup. Generally, linear penetration is more powerful against fragile targets, and percentage penetration is better against tough targets. For magic, a good rule of thumb is that Void Staff (40% penetration) is better than Sorceror's Shoes + Haunting Guise (40 penetration total) if the enemy has more than about 80 Magic Resist. If your champion has high AP ratios, the 50 more AP you get from Void Staff might make it better even at lower MR values.

One big thing to remember for physical penetration is, Last Whisper technically isn't penetration, it's an on-hit effect--this is so that towers aren't too easy to kill for someone with a Last Whisper (trust me, you don't want to see what a Tristana with Last Whisper used to be able to do to towers. >_>) That means that linear armor penetration can be very valuable even with high-armor enemies, since it'll help you do more damage to towers.

One last caveat: the way penetration stacks makes it very inefficient to buy both linear and percentile penetration. Penetration is calculated linear reductions and penetration first, then percentile off of what's left, because otherwise it's far too easy to get full defense penetration; as a result, the more linear penetration you have, the less benefit you get from percentile. Decide early on what kind of penetration you're going for, and stick to it.