what do you consider a "good" AC?

[bret]

For wizards, at higher levels it might be a better idea to go the Cloak of Major Displacement route. Give your enemies a high miss chance, since in my experience the AC doesn't keep up.

For the melee people, it would be nice to only be hit 1/3 of the time or less. An AC of 15 + level isn't too far off from that.

 

[Pax]

I consider a "Good" AC to be, anything that gives the "typical opponent" no better than 50/50 odds of hitting you with each swing. This,of course, varies.

At low levels, against monster attack bonusses of +2, +3, +4, a 14 or 15 AC will do fine.

At mid levels, when you start facing +8, +10, +12 ... 20 AC is "good".

At higher levels, when you start facing attack bonusses of +30, +40, +50 ... usually it's impossible to keep up with the AC-vs-AB race, but a 50-60-ish would seem to work reasonably well.

 

[Fenes 2]

IMHO, a good AC depends on the campaign, not only on the level. I personally use few monsters as opponents, and magic is rare. In one campaign AC20 is good at level 10 (masterwork mithril plate plus large shield), since we lack spellcasters in the party (only a bard and a paladin) and have no magical ac items. Consequently, the opposition is also not decked out with magic items, and it kind of evens out.
In another campaign at level 13, AC 20 is respectable, with a duelist/bladedancer reaching 34+ while the barbarian reaches 17, with the party sorceress beefing up everyone with Mage Armor. Again not much magic armor or AC items around.
In both campaigns, combats are usually divided into "main fights" and "fodder". Main fights are drawn-out fights against custom-built NPCs with matching abilities, while fodder is dealt with by playing a couple rounds at most before switching to narrator mode for the mop-up (unless the dice really went bad for the party).

What is a good AC in one campaign may be tissue paper in another, and invulnerabilty to melee and ranged attacks in a third - it all depends on the particular campaign, DM and group.

Edited level 10 instead of 20 - darn typo.

 

[dcollins]

My 30th level monk's AC is 91.

I don't use the Epic book, so maybe there's something in there that changes things radically. However, to date I've still never seen anyone claim an AC of 50 or more that didn't (upon presenting details) have some significant error in their calculation: either in the use of stacking rules, house-ruled new magic items, nonstandard equipment valuation, and/or counting a series of extremely situation-specific modifiers into their claimed AC.

 

[Gryphon]

Two Variations

I have a Ranger in a low magic world and it annoyes the hell out of me that i have an AC of 19, +3 AC bonus and +6 Dex. I can't enter combat with a hope of not being tonked all over the place.
Flat Footed Base AC 13
I have to sneak about in front of the party and attack from range and then disapear befor they can get into melee combat.

By comparison I am using a fighter paladin in a FR campaign, he is a similar level but has a much better AC of 28.
Mithral Plate Armour +3 Large Adamantite Shield +2, dex +2, and ring of natural armour +1. Flat footed AC of 24.
I still get hit every melee just not every single attack like the ranger suffers.

I think the first DM was terrified of giving out any protection magic because he felt that the monsters could not hit us. So when we started to get into encounters with single difficult to defeat monsters, like and aboleth we got mullered, over and over again. To the extent that he said that the new rules were rubbish etc etc.

It took ages to convince him otherwise.

So to the point, the AC of 19 at 15th is pants, and the AC of 28 is good enough.

 

[Fenes 2]

Which is why I, with similar ACs in my game, take care not to run monsters or other opponents right out of a book that was written with the assumption that magic protection was all over the place. I could, as the DM, easily make you feel that AC 28 was not good enough, or that AC 20 was overpowered, just by adjusting the enemies.

 

[The Souljourner]

I like the Level + 15 rule. That's fairly accurate, though slightly low for fighter types perhaps. AC 19 is definitely crap at 14th level. Most things you fight at that level are going to have +20 or so to hit, and thus will be able to power attack the crap out of you.

As for the guy who's in the low magic campaign - D&D was built on the assumption of a baseline amount of magic in the campaign. Anything seriously deviating from that requires a lot of manipulation on the part of the DM.

Assuming the guy was right who said 150k for a 14th level character, you can easily see how that could translate into AC for a fighter - give him a +6 weapon (+4 and holy or whatever), that leaves 78k for armor. Full plate +5 is about 26k, large shield +5 is about 25k. Amulet of natural armor +3 is 18k, and some miscellaneous stuff for about 9k more.

That gives our 12 dex fighter 34 AC. Perfectly reasonable equipment choices, and he has a +6 weapon as well. Of course you might want to adjust it down somewhat, since you'd probably end up with a shield +4 or +3 with some other ability, and the same with the armor... but all in all, 30+ is perfectly reasonable if you're running a standard campaign. 19 is definitely WAY WAY too low, unless your DM is specificaly straying from what is standard, in which case he needs to take that into account when he creates adventures for you.

-The Souljourner

 

[Fenes 2]

19 is definitely WAY WAY too low, unless your DM is specificaly straying from what is standard, in which case he needs to take that into account when he creates adventures for you.

You can bet all you have that I take the AC of our level 13 barbarian (13 to 17) into account when I design my adventures, just as I take the AC of our level 13 duelist/blade dancer (18 to 34), the spells of our spellcasters, the backgrounds and motivations of the different PCs, the wishes of the players and my metaplot into account when designing adventures.

Really, adjusting some enemies is the least of my work when preparing for an adventure.

 

[Spatzimaus]

Try 11 + level + Str + 1 (Weapon Focus) + level/4 (weapon enhancement bonus) + 2 (for miscellaneous buffs).

Yep, although you can usually assume that your own armor enhancement bonuses, buffs, and Dodge balance those. I specifically only count self-buffs; if you have to rely on the Cleric for it, then your opponent can do the same offensively.

Let's just call it 15+level for a 50/50 chance at high levels then.

The difficult part is, you can't just count pure AC. For example, I have a level 15 Psychic Warrior-type. Her AC is only 27, but she can also cast Displacement (50% miss chance), Inertial Barrier (Stoneskin), Vigor (18 temporary HP buffer for 1 power point), and Improved Biofeedback (take the first 10 points from each attack as subdual). So, while a given attack may get past the AC, it still has a low chance of actually hurting her.

 

[Dingleberry]

I know I'm stating the obvious, but it's always important to remember that even if you'll be hit on the first swing 19 out of 20 times, even a crappy AC can help save you from iterative attacks.