Armour Class in Dungeons & Dragons 5E

One of the bigger changes to the game in the new edition of Dungeons & Dragons concerns Armour Class.

It’s function hasn’t changed: the better (higher) your Armour Class, the harder you are to hit. When an attack is made, the attacker rolls a 1d20 and adds their attack bonus; if the result equals or exceeds the target’s Armour Class, the target is hit.

Although its function in the game hasn’t changed, it doesn’t just keep going up and up and up like in 3E and 4E. A major factor in the new edition’s design is Bounded Accuracy, which means that target numbers can’t change too much. Within the game, this translates to most Armour Classes being in the range of 10 to 20.

When a monster or character goes outside those ranges, you generally can assume there are magical items or spells involved, or the monster is special in some way. In the Basic Rules, the best Armour Class is 19, held by an adult dragon. The Hoard of the Dragon Queen Online Supplement has two monsters with an Armour Class of 20 – a helmed horror and a roper. Nothing in those documents gets better. Almost nothing in the Monster Manual exceeds 20.

This is, in many ways, similar to the original Dungeons & Dragons design, where monster Armour Classes were all in a very limited range: basically from 2 to 9. In those days, instead of providing a target number, they provided a chart reference; you’d cross-reference the Armour Class with the level or Hit Dice of the attacker to see what the target number was. Making Armour Class into the target number was one of the things the 3E designers got absolutely right. Historically, using a look-up chart for Armour Classes allowed non-linear progression of the target numbers, but that concept was largely abandoned by the time original D&D was printed.

With Bounded Accuracy in place, this has several implications to how Armour Class is calculated. Drawing on the terminology of previous editions, you have a Base Armour Class which then has several Armour Class Modifiers applied to it before you get the final result.

In 3E, your Base Armour Class was 10, and then everything else modified it: Armour, Shields, Dexterity, Spells, Amulets, Rings, and so on. In 4E, you also gained a bonus to it equal to half your level.

This is not how it works in 5E. Instead, Armour, Spells or Special Abilities provide you with a Base Armour Class, which is then modified by a very limited number of sources.

If your character has several ways of calculating their base armour class, you only use one method.

Here are a few examples of Base AC calculations:

  • No Armour: Base AC = 10 + Dexterity modifier
  • Leather Armour: Base AC = 11 + Dexterity modifier
  • Chain Shirt: Base AC = 13 + Dexterity modifier (max +2)
  • Plate Mail: Base AC = 18
  • Mage Armour spell: Base AC = 13 + Dexterity modifier
  • Barbarian Unarmoured Defense
    ability: Base AC = 10 + Dexterity modifier + Constitution modifier
  • Monk Unarmoured Defense ability: Base AC = 10 + Dexterity modifier + Wisdom modifier
  • Sorcerer Draconic Resilience ability: Base AC = 13 + Dexterity modifier

Meanwhile, there are several ways of further modifying your Armour Class. A few examples of these

  • Shield: +2 bonus to AC*
  • Shield of Faith spell: +2 bonus to AC
  • Shield spell: +5 bonus to AC
  • Half Cover: +2 bonus to AC
  • Three-Quarters Cover: +5 bonus to AC
  • +1 Armour: +1 bonus to AC
  • Ring of Protection: +1 bonus to AC; requires attunement
  • Bracers of Defense: +3 bonus to AC when not wearing armour or using a shield; requires attunement
  • Arrow Catching Shield: +1 bonus to AC against ranged attacks; requires attunement

There is at least one unusual exception to how AC is calculated:

  • Barkskin spell: Your minimum AC is 16.

*: The description of shields is unusual as it says it modifiers your base AC, but for most intents and purposes you can just treat it as a regular modifier.

As you can see, a multiclass Barbarian/Monk does not get to add all of their Dexterity, Constitution and Wisdom modifiers to the Armour Class! They have three ways of calculating their base AC, but can only choose one. However, they can benefit from as many other bonuses to AC as they like.

All the other modifiers stack; they aren’t split into several types of modifier like in 3E. (The one exception is that you can’t benefit from the same effect twice; if two clerics cast Shield of Faith on you, you only get a +2 AC. Multiple copies of the same spell do not stack!)

So, why can’t you just apply modifier after modifier and end up with a fantastic Armour Class that requires a natural 20 to hit? Well, you can in limited circumstances. However, there are three major restrictions on increasing your AC.

The first is that there aren’t all that many ways of modifying AC. Although several magic items in the Dungeon Master’s Guide do so, it’s something that the designers kept an eye one. +1 magic armour is sort of hard to find, but +3 armour is rare and precious, and +5 armour? It doesn’t exist!

The second is attunement. Magic items that provide powerful effects (and most permanent items that affect major numbers on your character fit into that category) have the limitation of “requires attunement”. The rules state that a character may have a maximum of three items attuned to them, so you are limited in that sense as well.

The third is concentration. Ongoing spells that provide bonuses typically require the caster to concentrate on them. That means that the caster can’t have any other spells requiring concentration at the same time. One character could get the benefit from a few spellcasters all providing them with armour class bonuses from different spells, but that will be the exception and not the rule, and the rest of the party wouldn’t be benefitting. It should be noted that there are very few spells that provide a bonus to AC in any case.

Honestly, the best way of increasing your Armour Class? Get behind an arrow slit! They provide three-quarters cover. Unfortunately, dungeon designers typically don’t design their dungeons with arrow slits the characters can take advantage of…

The flip side of this is to consider the range of attack bonuses. Just taking a quick flip through the Basic DM Rules, I see attack bonuses in the range of +0 to +14 (crab to adult dragon), with most being in the range of +3 to +7. A player character can probably expect at high levels to get a regular attack bonus of +12, assuming a 20 in the appropriate ability score, the full +6 proficiency bonus and a +1 weapon. Spells, items and abilities may push it a few points higher.

So, that’s a brief tour of how Armour Class works in the new edition. If you’d like to compare how AC worked in previous editions, I have articles on Armour Class in Original D&D and AD&D, AD&D 2E and D&D 3E. This is unlikely to be my last word on the topic, as my analyses are anywhere but complete!

Armour Base AC Type
Padded 11 + Dex modifier light, stealth disadvantage
Leather 11 + Dex modifier light
Studded leather 12 + Dex modifier light
Hide 12 + Dex modifier (max 2) medium
Chain shirt 13 + Dex modifier (max 2) medium
Scale mail 14 + Dex modifier (max 2) medium, stealth disadvantage
Breastplate 14 + Dex modifier (max 2) medium
Half plate 15 + Dex modifier (max 2) medium, stealth disadvantage
Ring mail 14 heavy, stealth disadvantage
Chain mail 16 heavy, stealth disadvantage, Str 13
Splint 17 heavy, stealth disadvantage, Str 15
Plate 18 heavy, stealth disadvantage, Str 15
Shield +2 modifies Base AC

21 comments

    • McCain

      It’s not an assumption. Considering characters in 5e get 2 attribute points to spend every four levels (assuming they don’t go for feats, which are a whole ‘nuther can of worms), characters that start with a primary attribute as low as 14 can have it up to 20 by level 12. It’s not even in the realm of “crazy min-maxing shenanigans”. Granted, the increased scores don’t have QUITE as much of an effect as 3.5, from my feelings about 5e, but maxing a primary attack / casting stat in the course of leveling a character is pretty reasonable.

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      • Quartz

        It’s most definitely an assumption. Consider a 5e game where everyone takes feats instead of stat increases. At high levels you might end up with one 18, but a 20 is going to be vanishingly rare.

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    • merricb

      A large part of the reason for assuming a 20 stat is that the default rules for D&D 5E do not include feats – they’re an option dependent on the DM. Most characters are going to have at least a 16 in their primary ability score at first level, and the use of two stat increases to get it to 20 by the highest levels does not seem unjustified. Note that 20 is the absolute maximum a non-barbarian can have their ability scores – a long way from the 30s that 3E and 4E had.

      Even if the character never increases their ability scores, the 16 means their attack bonus will only be 2 points below what I state above.

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    • Grant

      In the article (and the rules, PHB pg 14) you get either Unarmoured Defense or Draconic Resilience. They don’t stack, but provide 2 different bases, from which you get to choose which one to use.

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  1. Kervalin

    Would an ac of 27 be possible at level 6 playing in a 5th edition game. GM is pretty good at most rules I notice our cleric with an ac of 27 walking around. Writen on his sheet. Do I say anything or just do my own thing.

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    • MerricB

      It’s basically almost impossible to get an AC of 27. 21? Yes. 27? No. Some eldritch knights manage to get that briefly through the use of the Shield spell, but that’s about it. (If the character has somehow managed to find every AC magic item, perhaps, but very, very unlikely). I would bring it up – perhaps he’s adding Dex while wearing heavy armour, which isn’t allowed.

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      • Quartz

        Full Plate +3, Shield +3, Cloak of Protection +1 will get you AC 27 assuming you allow them to stack. But a 6th level PC shouldn’t have those.

        Dwarven Plate + Shield + +1 item will get you AC 23.

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      • Captain

        AC Cannot go above 23. So 27 is illegale. If there is any exception to this (like the shield spell maybe), I would like to know.

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    • Del

      So, I realize this thread is 8 months old, but I just thought I would mention something because it happened to me. I was unaware of exactly how AC worked in 5E. The last time I played was 20+ years ago. I rolled a rogue and joined a group. When the DM asked me what my AC was, I said it was 25. He asked me how in the world a level one rogue in leather armor had an AC of 25. I explained to him I had a base AC of 10, was wearing leather which was AC +11 and my DEX bonus was +4. That adds up to 25.

      Everyone had a big laugh, except me. What I learned that night was that in 5E, the 11 AC stated in the PHB for leather armor BECOMES the base AC, not adds to it. ::DOH!:: So, my REAL AC was 15 and not 25.

      I only mention it because perhaps that player with a 27 AC actually only had a 17. Much more reasonable. Right?

      Anyhow, I love this site. Full of so much info.

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  2. Henry Lancelot McCulloch

    A cleric, or for that matter many classes, can obtain a 27 AC without too much craziness if he/she has tons of magic items. But that’d only be If the DM is handing them out like candy. Easy/quick math. A cleric, or any class that can wear heavy armor can get:

    18 AC for plate
    + 2 ac for a shield = 20 base AC right off the bat.

    To gain the remaining 7 AC they’d need a cloak of protection or a ring of protection or an ioun stone; all of which grant a +1 defense.

    Add ONE of the above items to magical +3 plate armor and magical +3 shield and voila: 27 AC
    If they cast shield of faith and manage to keep it up through combat that’d boost up to 29 AC.

    For classes that can’t wear heavy armor or shield there are also bracers of defense +2 that they could wear to get close to the same #.

    Warriors/Paladins (or rangers if they took the feat to get heavy armor) could have the same gear and get an extra +1 AC from the ‘defense’ Fighting Style to boost their #’s further. Or multiclass 1 level into them and pick up the fighting style.

    It’s verrry unlikely in my opinion that they would/should be rolling around with that much AC though at lvl 6 and would be unlikely to have +3 magic items. So, with attunements in mind (since you can only equip 3 items that are say attunement in their description) I’d put money on it being a lot of little items rather than the big ones. IE:

    +1 Plate armor
    +1 Shield
    +1 Cloak of Protection (Attunement)
    +1 Ring of Protection (Attunement)
    Ioun Stone of Protection (Attunement)

    These 5 magic items would all be things that could likely be found during lower level adventuring and he just got lucky and scooped all the defensive related items. These would only bring him to 25 AC, it’s true, but then he could be assuming he’ll cast shield of faith on himself and writing down 27. He’d just remember that if he hadn’t put it up yet, he’d be two lower? That seems the most likely to me. 😀 But honestly….. I’d still ask. It’s all about how you approach the question.

    If you say ‘ohhhhh wowwww, 27 AC how did you manage to get it so amazinggggggly high!’ then your fellow player is more likely to gush about how it’s that high than if you say ‘pffft 27 AC yeah right, clearly you suck at math or must be cheating.’ Anyways, hope that helped.

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  3. Matthew

    I’m working on a DEX Fighter dual wielder. I’d be happy to make 24 AC. Everything is going into DEX and CON and a few feats, so she should be pretty durable.

    One can only hope.

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  4. imicles

    Although I appreciate the concept of having less extreme discrepancy between characters (3.5 or PF example: one mini-maxes to 25 while others stagnate around 19), I do not appreciate this new armor table in the 5th edition. A Fighter with some Dex bonuses will most probably not get to apply it to AC, as opting for Base armor 16+ is better (you can begin level 1 with Chain mail). Characters with over +2 Dex modifier will all stick with Studded or less.

    Padded, with a Stealth Disadvantage, really.

    A half-plate, better than ring mail and costing a whopping 750 gp, is a Medium armor.

    Sorry, I am not impressed. I love the 5th edition overall, but weapons and armor balance have not been improved in my book.

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