Whenever I'm talking to people they're like, "Armor counters my armor pen."
But when I'm in game I'm always thinking, "I need armor pen to deal relevant damage because they bought armor."
And it's just confusing because it's two very different, conflicting mindsets.
Slamurai Jack2 votesIt depends on what kind of armor pen you're talking about. %armor pen like on the Last Whisper items and Darius E passive counters armor because it effectively makes a certain % of your opponents armor worthless. The more armor they have, the greater amount of armor you're effectively ignoring. You have 30% Armor Pen and the enemy has 200 armor? You're ignoring 60 of it. They only have 100 armor? Then you're only ignoring 30 of it. On the flip side, flat armor pen is countered by building armor because you're ignoring a smaller % of your targets armor the more of it they have. You have 40 flat armor pen and your target has 80 armor? You've effectively removed half their armor. You have 40 flat armor pen and your target has 200 armor? You've effectively only removed 25% of their armor.
TL;DR Flat armor pen counters squishies, % armor pen counters tanks. Build armor to counter flat armor pen and build health to counter %armor pen.
67chrome2 votesTo add to this: the %damage increase you get changes pretty dramatically based on how much armor you're penetrating.
30 armor penetration vs. 30 armor causes you to deal true damage, or treat a target that took 76.923% damage as one that takes 100% damage from physical sources. That increase works out to exactly 30% more damage.
30 armor penetration vs. 300 armor causes you to treat a 25% damage from physical champion as ~27% damage from physical, which is ultimatly only a DPS increase of ~8%.
Worth noting base armor is ~20 @level 1 for most champions and even Sona exceeds 75 @18, so flat penetrations are always going to have enough armor to work with.
Alternatively: 30% armor penetration vs. 30 armor is only ignoring 9 armor, or treating that 76.923% damage from physical target as a 82.645% damage from physical target (a DPS increase of ~7%). 30% armor penetration vs. 300 armor treats a 300 armor foe as a 210 armor foe though, or 25% damage from physical to 32.258% damage from physical: an increase in DPS of ~29%.
So %penetrations are a counter to armor, armor counters flat penetrations. Those stats dynamically change the gold-to-power value of one-another (where 10% more DPS from AD/AS/AP is always going to mean 10% more DPS regardless of how much armor/health/%AS slows/MR your opponent does or does not have).
Quepha2 votesFlat armor pen adds way more to your damage against low armor targets. % armor pen (especially % bonus armor pen) adds more to your damage against high armor targets.
Build flat pen to assassinate squishies, but it's almost worthless against armor stacking tanks. Build % pen to shred tanks, but it adds almost nothing to champs that aren't building armor.
XxxLumberJackxxX1 votesHealth counters armor pen the best. Armor pen counters Armor. You need lots of armor pen to counter lots of armor.
Rock MD1 votesHealth counters armor pen the best. Armor pen counters Armor. You need lots of armor pen to counter lots of armor.
That's what I tell people and they're like, "Nah man armor counters armor pen."
But then they point out the less armor you have the more effective armor pen is.
And then it's worth noting that health will probably do more for you than armor.
Sniperkaj1 votesThey are right, and you and Lumberjack are wrong. It is simple mathematics, and that cant be argued with. Flat armor pen is ALWAYS countered by armor. If the enemy have 40 flat ArmorPen, you are better off building 40 armor than the same gold worth of health. Its a fact, and the posts above me have the maths. For %armor pen, whether it is total or bonus armor,, it is more complicated, but generally speaking it makes sense to buy health, especially if it is over around 40 %
TL;DR: YES, armor counter flat armor pen, this is mathematically true.