When does building armor pen. become more cost-effective than building attack damage?

I'm looking for hard math, not educated guesses.

Some things I've been looking at:
At what enemy armor level is it more cost effective to build Last Whisper over Black Cleaver?
At what enemy armor level is it more cost effective to build Last Whisper over Blood Thirster?

This is assuming standard AD carry masteries in offense, so +10% armor pen, +6 armor pen. Also assuming 0 armor pen runes (not everyone chooses to run them on ad carries)

• Commented Apr 4, 2012 at 13:16
• Commented Apr 4, 2012 at 13:17

I think the other posts pretty much sums it up, it is really situational. I found this which is in an in depth comparison between last whipser and black cleaver.

Copying the tl;dr from the linked article: Everything in League of Legends is situational. Neither Last Whisper nor The Black Cleaver is superior to either in all situations; learn to think analytically and determine in what situations one will do more damage than the other.

Edit: Link contains hard math, result is still "it depends". The lower armor and longer engages the better black cleaver turns out and of course vice versa.

• Thanks this is definitely what I was looking for. I definitely realize that it's situational :) Commented Apr 4, 2012 at 19:21

Two things that weren't mentioned is your team composition and the use of abilities in teamfights. Black Cleaver provides 0 armor penetration on the target. Rather it provides an armor reduction debuff on the target that stacks. This means if your team is AD heavy (solo top lane is AD like Riven, Garen, or GP) then having Black Cleaver as a Ranged AD Carry allows you to "tag" the target with the debuff allowing yourself and your AD bruiser to do more damage. Last Whisper on the other hand only affects what you see for the target's armor, their actual armor number is unchanged for everyone else. Also it is effective for your autoattacks as well as your abilities. So for instance if you are trying to poke each other before a full on teamfight starts using abilities like Ashe Volley, Caitlyn's Piltover Peacemaker, etc. Your abilities will have the full effect of a Last Whisper but zero effect of the Black Cleaver debuff, since most abilities do not provide on-hit effects for Ranged AD carries.

If the enemy is building Thornmail, it's a good idea to get more Armor Pen so you can kill them faster and do less damage to yourself in the end. Whenever your team is very reliant on AD, you should get a Black Cleaver so that all your teammates can do more damage. But, if the enemy has so much armor that you can't hurt them properly, then you should get Armor Pen, otherwise stick with AD.

I know that this topic is old but I was looking for the same answer ;-) Anyway no one is responding to your question so i decided to do the maths.

It started with some Excel graph where i compare 2 runes build (considering only Marks and Quintencences ) and including the 10% armor penetration and 6 flaf from masteries

Full Pene build => +25 Armor penetration ==> (Pene)

then there is 2 thing that varies : Your total Attack damage (not considering runes) and the armor of the target

Finaly i deduced 2 formula :

1) Calculating a witch point of Attack damage The Armor Penetration build become more effective than the Full AD build for a fix amor value:

``````Attak = AD((94 + Armor*0.9)/Pene) - 1)
``````

2) Calculating a witch point of Armor The Armor Penetration build become less effective than the Full AD build for a fix Attak damage:

``````Armor = ((((Attak/AD)+1)*Pene)-94)/0.9
``````

...............................

``````Example 1 : I'm an AD Carry and there is a tank with 150 Armor

Attak = 16((94 + 150*0.9)/25) - 1) = 130.5

==> So i have to reach 130.5 Damage for my Full Pene build to be more effective.
``````

................................

``````Example 2 : I'm an AD Carry and i have 150 AD (not considering runes)

Armor = ((((230/16)+1)*25)-94)/0.9 = 183.75

==> So if the target has more than 183.75 Armor my Full AD build is more effective.
``````

.................................

Conclusion : The more Total damage you got the better is the Penetration build. But the more Armor the target has, the less the armor penetration is effective.

• Not sure I agree with your conclusion. Ignoring 10 armor gives the same DPS increase if your target has 1000 armor as when they have 10. Commented Oct 3, 2012 at 11:27
• gaming.stackexchange.com/questions/10244/… Commented Oct 3, 2012 at 11:28
• Nop it doesn't cause in the formula u can the that the damage reduction from 10 armor to 0 armor is reduce by 9% ( 9% => 0%)when from 1000 armor to 990 is 0.09% (90.82% => 90.91%) Commented Oct 3, 2012 at 14:27
• @RavenDreamer Let's assume we have an attack that deals 100 dmg and we have 20 armor penetration. Our target has 20 armor and 1000 health. Before penetration our attack is going to do 83.333 damage, after penetration it will do 100 damage. This means that we're going from 12 attacks to 10 attacks to kill our target, a 16.667% advantage. Now our target has 150 armor, our attack is going to do 40 damage before pen, 43.478 after pen. We're going from 25 attacks to 23 attacks, an 8% advantage. Armor pen is indeed more effective the less armor someone has. Commented Oct 3, 2012 at 18:11
• @Snuffleupagus By your own numbers - the same amount of armor penetration reduced the required number of attacks by 2 in both cases. That is more important than the relative increase percentage wise. Commented Oct 3, 2012 at 23:09