How Much AC is enough?

[the_archduke]

I have heard it said that optimizing for AC is a sucker's game. In my experience, AC is the single most used defense in the game. And when you get hit you lose HP. And when you lose enough HP you die. I don't want to argue the point, assume that AC is what I want. How much AC do I need at each level to make optimizing it worthwhile? And is it possible to get enough AC to walk around without worrying about anything but 20s?

My current character is a Meditant psychic warrior. At level 3 I have an AC of 22 (10 base +1 dex +4 wis +1 dodge +5 armor +1 deflection). Between gear, inertial armor scaling 1 AC every other level, wis and dex to AC, the scaling bonus from Meditant and eventually another scaling bonus from the Ascetic path, I will have an AC in the mid 60s by level 20. Is it enough? Or am I chasing something unobtainable?

[Seerow]

Something like 15 + 1.5*level is a good benchmark I try to have defensively minded characters aim for.

So level 1 = 16
Level 5 = 22
Level 10 = 30
Level 15 = 37
Level 20 = 45

Ideally this AC should be (most if not all) touch, and have Uncanny Dodge to keep dex to AC for most situations where you would normally lose it.

There will still be outliers that make your AC effectively useless (which is why most people recommend against bothering with AC at all, since it is expensive to get it up even as high as mentioned here, and it will be useless occasionally after that investment), but it should be enough to keep a useful level of miss chance against an average on CR monster.


Basically what I'm trying to say is, the AC you are going for should be fine. There are probably better ways to invest the resources you are putting into it, but it'll be more than enough to deal with your average enemy.

[Der_DWSage]

Another reason people say AC is a sucker's game is that there are very, very few reasons for someone to attack the heavily-armored tank when there are far more vulnerable party members to focus on instead. You have enough AC that even the Tarrasque has trouble opening you up like a Pringles Can? That's great! Since after his first full-attack he realized he's not touching you, he's going to go and focus on your party members who focused more on damage.

A third reason is the fact that you're generally making a trade-off for this kind of AC in the form of 'not doing much damage.' Psychic Warrior is a distinct exemption to this with their scaling AC and being able to add two stats to AC, but most that try and chase that route have to pick up a shield and accept that their damage output is going to sorely lag behind anyone with a two-handed weapon. Two-weapon fighting with the shield can pick that back up, but it's still a slow game at that point.

That said, 60 AC is plenty for level 20. You're probably going to attain your wish of having AC so high people only hit you on a 20 quite soon. Just be ready for them to ignore you once you do, and going for less protected teammates.

[ericgrau]

Monster attack bonus is roughly around CR * 1.25, so 20 + CR * 1.25 is plenty. Maybe 25-30 + CR * 1.25 if you really want to be unhittable. So 55 AC by level 20 is plenty so 60 is certainly plenty. And generally CR * 1.25 + 15 is decent, meaning 40 by level 20.

AC also tends to both suffer and benefit from diminishing returns. A bunch of +1s are usually worth it on anyone, even casters. Find as many sources as possible with different types. +2s and up get more and more costly and then you have to figure out how much is still worth it at your level.

I think AC gets maligned in forums because discussions tend to speak in absolutes and extremes. It's actually a lot more fuzzy than that and it's usually a good idea for everyone to pick up some +1s at minimum, if not more. Good bang for the buck and it will get used some amount greater than zero, simple as that. If you're looking only at the worst corner case or idealized scenarios, you're figuring it out completely wrong.

[Fouredged Sword]

The number I hear thrown around is that you should be between AC = level +13 and AC = level +23. This breaks down at low and high levels, but if you have less than AC = Level +13 or over AC = Level +23, you are unlikely to really benefit from an additional point of AC, as you are ether going to be hit or missed already.

[Psyren]

The key with AC (and DR for that matter) is that the dangerous melee monsters generally go for "thousand cuts"-style combat, i.e. the bulk of their damage comes from 3+ smaller hits rather than one big hit. So even if your AC isn't high enough to stop that first iterative or even their primary attacks, so long as it has a good shot at preventing the secondary attacks/iteratives from landing, it's doing its job.

For example, a Lhaksharut is CR 20; its attack sequence goes +32/+27/+22/+17. Optimizing to beat that first iterative will take a lot more resources than simply accepting that the first hit has a decent chance to land and beating the rest.

As a second and more extreme example, the Tarrasque has 6 attacks. 5 of these are primary, so optimizing to beat them is difficult. However, its 6th attack, the tail slap, is also the one with the longest range (60ft. as opposed to 30) so this is one that pretty much everyone in the party will need to worry about. Its ranged spines are also much lower and have long range, so those should be worried about too.

[Spore]

Also AC starts to loose value when your enemy needs to roll higher than a 10 to attack. That's because every AC beyond that becomes more expensive while simultaneously not providing as much benefit as before. Reducing your chance to be hit from 10% to 5% is the same jump as the reduction from 20% to 25%.

Personally I keep my saves as priority #1 (saving from debuffs and other stuff), positioning and mobility as priority #2 (not standing in no-save stuff) and AC as priority #3 (deterring loose minions to not attack me). I prefer miss chances and protection (spells).

An AC 40 Fighter is probably well defended. But I reckon that my AC 27, saves 15+, sanctuary'ed up (DC 18) airwalking Pathfinder Oracle is better protected. And all that with four spells (sanctuary, 2x Magical Vestment, Airwalk) a class feature (Spirit Shield = Breastplate for hours/day with no weight and enchantable) and a magical shield (Mithril Shield). A Fey will scare him and then cast Curse upon the Fighter's sorry behind dropping its will save further just to finish up with a dominate person.

[Necroticplague]

Also AC starts to loose value when your enemy needs to roll higher than a 10 to attack. That's because every AC beyond that becomes more expensive while simultaneously not providing as much benefit as before. Reducing your chance to be hit from 10% to 5% is the same jump as the reduction from 20% to 25%.

Depends on how exactly you look at it. In that first case, you're reducing their chance to hit you by a solid 50% (they're now half as likely to hit you), while in that second case, you're only reducing it by 20% (they're still 80% as able to hit you as before).

[Spore]

Depends on how exactly you look at it. In that first case, you're reducing their chance to hit you by a solid 50% (they're now half as likely to hit you), while in that second case, you're only reducing it by 20% (they're still 80% as able to hit you as before).

You are correct but the game is not just defending from physical attacks. The only time AC is important is vs. critfishing enemies.

[Psyren]

You are correct but the game is not just defending from physical attacks. The only time AC is important is vs. critfishing enemies.

It's also important vs. iteratives, secondary attacks, power attack, in conjunction with debuffs like shakened/sickened on the target etc.

[SowZ]

AC, like HP, is one of those things you should keep at a reasonable level and invest in moderately, but don't build around it too much or drop a lot of gold. That same amount of investment is better spent on miss chances and ways to mitigate attacks entirely like temporary etherealness, instant action teleports, stuff like that. There's too many ways for AC to be made irrelevant to rely on it as your primary defense at high levels. Of course, your AC will be attacked frequently enough that unless you have a very reliable alternate defense, you want a high enough AC that it is moderately difficult to beat.

[Psyren]

^ Agreed.

I think Seerow's Formula is a good rule of thumb personally.

[RedMage125]

You have enough AC that even the Tarrasque has trouble opening you up like a Pringles Can? That's great! Since after his first full-attack he realized he's not touching you, he's going to go and focus on your party members who focused more on damage.

That's some pretty impressive tactical thinking for a creature with an INT of 2.

[Der_DWSage]

Not really? 'Oh, this guy I'm chewing on is completely ignoring me. Meanwhile, this guy keeps shooting arrows in my butt. I don't like arrows in my butt. Especially since I think I'm healing over them. I think I'll chew on him now. Then I'll have Wizard Dessert.'

(We all know he's never touching the Wizard. Let the Tarrasque with an Int of 2 have his dreams.)

[Psyren]

Not really? 'Oh, this guy I'm chewing on is completely ignoring me. Meanwhile, this guy keeps shooting arrows in my butt. I don't like arrows in my butt. Especially since I think I'm healing over them. I think I'll chew on him now. Then I'll have Wizard Dessert.'

(We all know he's never touching the Wizard. Let the Tarrasque with an Int of 2 have his dreams.)

What level 15+ archer worth his salt would not have a flying mount or item though? Big T will need his spines or tail to hit that guy, both of which have lower attack bonuses and are far less dangerous because they can't initiate a grab/grapple.

Even if Big T does switch targets, he would waste at least a round, likely more than one, trying to crack the nut of the high-AC character before realizing he couldn't get to the meaty center. Even if Int 2 can eventually figure that out, it's still pretty dumb. What's more, many of the things that apply to AC also apply to CMD (e.g. deflection and dodge) so he's likely going to waste time trying to swallow that character too. And even if he succeeds in swallowing that character, they are can simply whip out a light weapon and cut their way out vs. half-AC. And the whole time, the archer and any casters are whittling Big T down at range.

[Spore]

That's some pretty impressive tactical thinking for a creature with an INT of 2.

Wolves hunt in packs with strategy...and they also have Int 2. Elephants remember the guy who has mutilated them from YEARS ago = instant aggro on sight. Which also points to the Int 2 critter charging the guy who has hurt them the most. Which is not the weird tin can man that tries his very best to scratch your hide.

[Psyren]

Wolves hunt in packs with strategy...and they also have Int 2. Elephants remember the guy who has mutilated them from YEARS ago = instant aggro on sight. Which also points to the Int 2 critter charging the guy who has hurt them the most. Which is not the weird tin can man that tries his very best to scratch your hide.

But they will also waste time wailing on a building/jeep/armored car/etc. even if it can stand up to their attacks. A bull can be easily distracted to go after the guy fluttering the cape while other folks stick spears in its flanks, or a rodeo clown can distract it away from a fallen rider while it is lassoed from behind. Your elephant can be fooled by someone dressing up similarly to the guy who hurt them. Int 2 doesn't mean "makes the best decisions" or "cannot be tricked/misled."

[Spore]

Int 2 doesn't mean "makes the best decisions" or "cannot be tricked/misled."

Nor does Int 18. :)

Aren't these Sense Motive checks by RAW?

[Psyren]

Aren't these Sense Motive checks by RAW?

Well hang on now, are we talking RAW or the real world? Because RAW doesn't say anything about an elephant's memory, or about creatures automatically switching to whoever damaged them the most. You're trying to have your cake and eat it here - either animals only behave the way their entries say they do (with any deviations being up to the DM in question), or they should be played realistically (in which case they can be somewhat easily fooled.)

[Spore]

Point taken. You CAN fool them into attacking the tin can. But then the tin can needs stuff BESIDES AC to provoke (Bluff as skill, particular feats etc.). That's the point we're trying to get across here. Focussing on damage and attacking what YOU seem fit falls better into place than focussing on AC and goading enemies into attacking you.

[Goblite]

A lot of the arguments against AC here are based on enemies ignoring you to attack less vulnerable teammates. While this is a legitimate concern I don't feel that a decent DM would really allow it to happen consistently. The DM would be sorely abusing metagame knowledge; his npc's would not know your AC or potential damage output or create strategies around how many hit points they expect to lose anyway- most thinking creatures don't like getting stabbed at all. A rogue npc might avoid a heavily armored foe but a fighter or barbarian likely wouldn't, nor would a wizard casually allow a tank to threaten them just because he doesn't expect to take much damage.

That said, lack of damage is a concern for a warrior class. There are a number of ways to balance your offenses and defenses. If you have both Combat Expertise and Power Attack you can easily switch between high armor class or high damage. A Defending weapon allows you to use its enhancement bonus either of offense or defense. There is a shield enhancement that lets you morph your shield into a tower/heavy/light/buckler as a swift action so you can either go longsword/towershield or suddenly 2hand your longsword with a buckler and a -1 penalty to attacks. Lastly, with a high AC you can feel free to attempt disarms, trips, grapples, overruns, etc... even without the improved feats because you likely won't get hit by the attack of opportunity you provoke.

As with many things the DM's style is really the deciding factor in what is most effective. DM's who throw nothing but huge monsters at you will see their ubercharging players shining as they dole out 20-40 damage per hit while a DM who likes to create enemies with Class Levels will see their more tactical players finding interesting ways to use their abilities.

[lsfreak]

A lot of the arguments against AC here are based on enemies ignoring you to attack less vulnerable teammates. While this is a legitimate concern I don't feel that a decent DM would really allow it to happen consistently. The DM would be sorely abusing metagame knowledge; his npc's would not know your AC or potential damage output or create strategies around how many hit points they expect to lose anyway- most thinking creatures don't like getting stabbed at all. A rogue npc might avoid a heavily armored foe but a fighter or barbarian likely wouldn't, nor would a wizard casually allow a tank to threaten them just because he doesn't expect to take much damage.

That works, IF whatever the PCs are fighting are largely random encounters. But PCs have reputations - or at least should - by the time the game really starts to pick up around 6th level. Civilians who see them fight will spread stories. NPCs who escape will bring knowledge of the PCs tactics back to their organizations or their masters. Eventually bards should just be able to use bardic knowledge to get information on them. If the PCs rely on certain tactics, they will be known.

Also, even just fight-to-fight, if a few people gang up on a fighter and all wiff their attacks, it should be pretty clear to all of them that he's untouchable. Especially if they rolled well. And in general those with high armor are less mobile, thanks to the -10ft speed penalty that comes with medium and heavy armor, so it's not an unreasonable assumption on the part of the NPCs that if someone is hard to hit, they'll be easier to move around and get to someone more vulnerable.

[SowZ]

That works, IF whatever the PCs are fighting are largely random encounters. But PCs have reputations - or at least should - by the time the game really starts to pick up around 6th level. Civilians who see them fight will spread stories. NPCs who escape will bring knowledge of the PCs tactics back to their organizations or their masters. Eventually bards should just be able to use bardic knowledge to get information on them. If the PCs rely on certain tactics, they will be known.

Also, even just fight-to-fight, if a few people gang up on a fighter and all wiff their attacks, it should be pretty clear to all of them that he's untouchable. Especially if they rolled well. And in general those with high armor are less mobile, thanks to the -10ft speed penalty that comes with medium and heavy armor, so it's not an unreasonable assumption on the part of the NPCs that if someone is hard to hit, they'll be easier to move around and get to someone more vulnerable.

If one of the enemies you are fighting seems untouchable, you'd just run away. I mean, maybe you can kill his companions, but then you have to fight him again, anyway. Either you think that if you gang up on him you can take him down, or else the fight is hopeless. Assuming the goal is to defeat the party, that is.

[Hrugner]

The high AC character does have the option to try and burn through an enemies attacks of opportunity allowing the rest of the party to move and cast freely. So, while they can't force the opponent to take all of their attacks against him, he can control a varying amount of outgoing damage from some monsters. Move through threatened area, attack with a whip I guess, attempting an untalented trip, that should be 3 attacks of opportunity none of which should hit. You won't be doing damage, but I don't think that's the purpose of the AC character anyway.

With a 60 AC I'd hope the character would grab the panther style and snake style lines. Provoke the heck out of your opponents, drop some retaliatory strikes, and get some use out of the AC that's probably 10 over what you need.