Calculating Armour Class (AC) is actually quite easy once you know how it works. Unfortunately, the key rules seem to be fairly easy to overlook, and therefore many players get confused about how to calculate their Armour Class when they have multiple bonuses from multiple sources. This post will endeavour to explain how AC is properly calculated to help dispel the confusion.
Chapter 1, “Step-by-Step Characters” of the Player’s Handbook discusses what your Armour Class (AC) is and how to calculate it, but the many options that players are presented with to modify their Armour Class can cause some confusion. Below is an in-depth look into the intricacies of this very important feature.
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There Are Two Kinds of AC Bonuses
The first and foremost thing that you have to remember about Armour Class is that there are two kinds of Armour Class bonuses in 5th edition. The first kind is not so much a bonus as it is a formula to calculate your Armour Class, and the other kind is a flat AC bonus that you can apply to any formula you have used to calculate your AC. Generally, features granted by your race or class (such as Unarmoured Defence or natural armour) will give you a formula, as will the kind of armour your wear. These features say “your AC equals”. Sundry items such as shields or rings of protection, on the other hand, simply say that you add whatever number to your Armour Class.
Formulas for calculating AC do not stack. If you have a natural armour formula and don a suit of armour, you can’t benefit from both at the same time. Likewise (and is an exceptionally common question), a tortle monk does not get to add their Dexterity and Wisdom modifier to their race’s natural armour.
The flat bonuses from sundry items do stack, with the principal exception that no item stacks with itself (yes, this includes shields, so dual wielding shields is silly unless you plan to use one to shield bash every turn). For example, a barbarian wearing bracers of defence would add the +2 from the bracers to his or her armour class (stacking with unarmoured defence) because the bracers are not a separate formula, they simply add a flat bonus.
Therefore, a barbarian with Dexterity 14 and Constitution 14, and wearing a ring of protection and bracers of defence, would have an AC of 17 (10 + 2 Dex + 2 Con + 1 ring + 2 bracers). If the barbarian somehow found a second ring of protection, though, he may as well give it to the wizard because he can’t benefit from two of the same item (in this case, though, it’s primarily because he can’t attune to a second item of the same name as one he already has). But, if the barbarian found a cloak of protection, then he could wear that as well and have an AC of 18.
Each Armour Class Formula is Mutually Exclusive
The second thing to remember is that any formula for calculating your Armour Class is its own, discrete calculation that is mutually exclusive to every other Armour Class formula. In other words, whenever you encounter a calculation method that states “your AC equals”, such as the monk or barbarian’s Unarmoured Defence, the Draconic Bloodline (sorcerer)’s Draconic Resilience, or your shiny suit of full plate armour, you cannot stick them all together.
For example, if you are a sorcerer/monk/barbarian multiclassed character, your AC does not become 13 + your Dexterity modifier + your Constitution modifier + your Wisdom modifier. You can only gain the benefit of one of the following:
- (a) the sorcerer option
- (b) the barbarian option or the monk option (whichever class you went into first, as per PHB 164)
Likewise, and to address a specific question that many shameless power-gaming munchkins often ask (and the reason why this article uses the header image that it does), a lizardfolk barbarian with Dexterity 10 and Constitution 18 (or a lizardfolk monk with Wisdom 18) who is not wearing any armour would have an AC of either 13 (from natural armour)[1] or 14 (10 + 4 from their ability), but not 17. This is because the natural armour bonus a lizardfolk receives does not stack with the barbarian’s (or monk’s) Unarmoured Defence; they are separate formulas. And if someone cast mage armour on the lizardfolk barbarian, the creature would have to choose between using this new Armour Class calculation or one of the other two options.
As an important side note here: even though the Armour Class formula for armour and the Armour Class formula for natural armour are mutually exclusive, you aren’t considered to be wearing armour with natural armour. This is important because it means that if the lizardfolk barbarian described above picked up a pair of bracers of defence, the creature could still benefit from wearing them because it is not considered to be wearing armour.
You Pick The Best Option
If you have access to several methods of calculating your AC, such as is the case for a lizardfolk barbarian, you pick the option that you want to use. If you are a lizardfolk barbarian and your Constitution modifier is higher than +3, you may wish to use the barbarian’s Unarmoured Defence option. However, if you are subsequently affected by an effect that reduces your Constitution score (and, therefore, your modifier), you can still choose to benefit from the lizardfolk’s natural armour. Likewise, if you take a level of fighter and decide to don a suit of mail[2] armour, you can then decide that the AC provided by the suit of armour is superior to the barbarian Unarmoured Defence ability, and take that AC calculation.
I’ll also take this opportunity to include a special reminder about Unarmoured Defence. If you gain the Unarmoured Defence feature from one class and later would gain it from another (for example, if you started as a barbarian and then took a level of monk), you do not gain this feature again from multiclassing (see PHB 164). In other words, the first time you gain the Unarmoured Defence option, that is the only version of that option that you can ever benefit from.
Step By Step
Now that we understand the various components of Armour Class, let’s look at how simple it is to calculate your AC.
Step 1: Figure out what AC formulas you can use.
Are you wearing armour? Do you have a class feature that offers you a way to calculate your AC? Make a list of the options. If you only have one option, skip to step 3.
Step 2: Figure out which AC formula is best for you.
Figure out which option gives you the best AC. If you are a mountain dwarf Draconic Origin sorcerer, for example, you may wish to wear a medium armour option instead of relying on Draconic Resilience.
Step 3: Add in your miscellaneous bonuses.
Are you using a shield? Are you wearing a ring of protection? Tally them up and add it to your AC.
Example: Giovanni the Tortle Monk/Barbarian
Giovanni is a tortle who grew up in the sewers beneath a metropolitan city, learning the secrets of martial arts from a great master who had been afflicted with lycanthropy by a wererat. He has a Dexterity 17, a Constitution 17, and Wisdom 14. His player wants to determine what Giovanni’s armour class is.
A tortle’s Natural Armour gives them a base AC of 17. Their Dexterity modifier does not apply to this. A monk’s Unarmoured Defence feature gives them a base AC of 10 + their Dexterity modifier + their Wisdom modifier. Giovanni therefore has two base AC calculations: the tortle’s and the monk’s. Each calculation is its own discrete entity; Giovanni can either take it or leave it, he can’t take a part of it here or there. Because the Unarmoured Defence calculation comes in at only AC 15 (+3 Dex, +2 Wisdom), the player opts to have Giovanni rely on his armoured hide in battle.
When Giovanni gains his next level, his player decides that the tortle has been learning to embrace his inner fury with his fighting style and so will take a level of barbarian. As barbarians also have an Unarmoured Defence feature, he once again considers Giovanni’s AC. Page 164 of the Player’s Handbook tells him that because Giovanni had Unarmoured Defence from the monk class already, he does not gain it from the barbarian class, and so even though that option would yield a higher bonus than the monk’s Unarmoured Defence (AC 16 to the monk’s AC 15), it is not an option for Giovanni. However, that’s ultimately a moot point because the tortle’s Natural Armour feature is still better than either of them, as it gives a base AC of 17. Therefore, there is no change to Giovanni’s AC.
Giovanni does not end up with an AC of 25 (17 + 3 Dex + 3 Con + 2 Wis). If that is what Giovanni’s player comes up with, then Giovanni’s player needs to read this article again.
Putting It All Together
Calculating AC in Fifth Edition is, more often than not, a matter of picking the better formula. While you can’t stack a barbarian’s Unarmoured Defence with a sorcerer’s Draconic Resilience, you can pick which one you wish to use. Separate AC formulas don’t stack, so a lizardfolk who is a draconic bloodline sorcerer/monk/barbarian with Dex 14, Con 14, and Wis 14 doesn’t automatically have AC 21; you would have to pick which method of calculating AC you wish to use: the lizardfolk’s natural armour (AC 15), the sorcerer’s Draconic Resilience (AC 15), or the monk’s or the barbarian’s Unarmoured Defence (AC 14). Once you have done that, you can look at the flat AC bonuses from other features or items, such as a shield (or the shield spell), which stack with everything else (except themselves). Remember to read your class features carefully to be sure that you are adding the correct bonuses.
Footnotes:
¹ Many people read “+3 natural armour” on page 282 of the DMG and assume that they can apply this to their lizardfolk player character. In fact, that chapter of the DMG is written specifically for creating NPCs, not player characters, and so this is inappropriate. To see how you should actually be calculating your lizardfolk PC’s Armour Class, consult page 113 of Volo’s Guide to Monsters, as Volo’s is a player resource. There you will find that the natural armour bonus is written as “your AC is 13 + your Dexterity modifier”. So no, you cannot be a plate-armour-wearing lizardfolk with AC 21 at 1st level.
² Also known as ‘chain mail’. Minor annoyance: ‘mail’ already means chain, as opposed to ‘plate’, which refers to a drastically different type of armour made with metal plates (as opposed to interlocking links). ‘Chain mail’ is a redundancy and ‘plate mail’ is an oxymoron. Not only that, it also makes the terminology more cumbersome. Please consider this the next time you talk about armour.
Special Note:
Dungeon Master’s Workshop is a Canadian publishing operation. This is reflected in how we spell armour (armor), defence (defense), and several other words—these are not typos, they are how these words are actually spelled. If your country spells them differently, that’s really not our problem. When Wizards of the Coast hires us to write “armor”, we’ll write it that way. Until then, God Save the Queen.
Changelog:
—Edit 2018/01/31: Clarified the first section due to misunderstanding about “bonus types”. This term, borrowed from a previous edition, was meant to demonstrate that different armour calculations (as well as two shields/rings) don’t stack. The plain language of 5th Edition can sometimes cause people to overlook the subtle nuances, and we thought applying a label to bring peoples’ attention to it would help clarify things. We got the point across for 99.9% of readers using that description, but we aim for 100% and so we’ve adjusted the section.—
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In reality, If anybody (squishy like a human or more robust like lizard folk) had leather armor outside of their natural skin; the leather would slightly improve their AC some.
If a dagger slashed at skin it would cut it easy because humans are squishy, but a dagger may also scratch a scale of somebody less squishy; and leather armor would protect either person to some extent.
I’m not saying this changes the rules as written, I’m just saying let’s use some common sense.
Here’s some strange factual reality from the real world: The mongols used to wear silk shirts under their armor because for some reason it could stop an arrow from piercing them better than the armor by itself. Silk shirt by itself, not good armor; silk shirt under armor, nice bonus. Think about that while contemplating this.
Thanks for the comment!
Interesting fact: the silk didn’t actually stop the arrow from piercing the person’s flesh. Rather, the Mongols wore silk under-armour because the fabric didn’t tear; it would wrap around the arrow as it penetrated the flesh. This made extraction easier, as the silk could be pulled and the arrowhead would come out with it.
The arrow could still hit something vital if it penetrated the armour, and it could still break ribs, sever an intercostal vein, puncture a lung, pierce the bowels and initiate sepsis, etc. It just didn’t have to be pushed out the other side like what often had to happen with other arrows.
Best!
the Archmage
okay heres what me and my dm argue over….
Natural armour of 17 (loxodon or lizard man, not important)
They put on +2 studded leather.
Is their ac 19 as the magic bonus a bonus? or is the magical bonus part of the armour and only useable while using its calculation.
Then same scenario except this time its studded leather with an artificers infusion, which gives a +1 bonus while wearing the armour, he’s definitely wearing it, but he isn’t using its calculation, so does his ac become 18?
Hi Hakon,
This is a very good question! Let’s look at the actual wording of the Natural Armour feature (emphasis mine):
“When you aren’t wearing armor, your AC is ## + your Constitution modifier. You can use your natural armor to determine your AC if the armor you wear would leave you with a lower AC. A shield’s benefits apply as normal while you use your natural armor.”
(## = 12 for loxodons or 13 for lizardfolk)
That’s pretty confusing, isn’t it? Sentence 1 says you can’t use your natural armour AC calculation if you’re wearing armour, but sentence 2 says you take whatever’s best. If a lizardfolk fighter with Dex 18 has the Defense fighting style and a set of +1 leather armour, that leaves us with two possibilities:
(1) The lizardfolk has two different AC 17 calculations (11 [leather] + 4 [Dex] + 1 [magic] + 1 [Defense] or 13 [natural armour] + 4 Dex)
(2) The lizardfolk has AC 19 (
11 [leather]13 [natural armour] + 4 [Dex] + 1 [magic] + 1 [Defense])Clearly, (1) is what is intended, but the way the rules are written doesn’t say that (2) is wrong.
The best advice that I can offer here is the same I offer whenever there’s a wonky rules interaction: the DM should make a ruling. If this were my table, I would rule that you add up all the AC calculations separately and then choose which one applies, as done in option (1). The armour’s enchantment only improves the ‘armour value’ of the armour itself, not a creature’s natural armour, and the Defense fighting style only applies when you are using artificial armour you’ve specifically learned how to move around in. Your DM may disagree.
Best,
the Archmage
One of the many reasons i prefer 2nd ed, its much clearer on things and more detailed, natural ac is a creatures innate/base ac, a a human/db/dwarf/elf etc are 10s, but take a pixie or fremlin for example, both have existing official rules to play as pc, complete book of humanoids, being tiny creatures they start with a higher natural ac than standard creatures because they are harder to hit, this doesn’t change if they wear approriate armor, base ac(nat ac) + dex + armors ac = pc ac, at least how it should be and is played at my table, shields also always add whether in hand or not, if u have it its on your body somewhere, back, hip, shoulder, another reason 2e sheets were better as it individualized all those things
Hello! This is exactly the clarification I needed, but I can’t find the ruling in my source books, I have a rules lawyer at the table who needs things pointed to in the books before he changes his mind. What book is this in? Thanks!
To answer Infernoschill,
It’s on page 14 of the Player’s Handbook, about midway on the right side of the page. To quote: “Some spells and class features give you a different way to calculate your AC. If you have multiple features that give you different ways to calculate your AC, you choose which one to use.”. If you want specifics for armor, it refers to chapter 5. I’m making a bit of an assumption in that it means specifically the entry about AC on Page 144, midway on the right side. Again to quote: “Armor protects its wearer from attacks. The armor (and shield) you wear determines your base Armor Class.” It specifically says BASE Armor Class, which I personally presume to mean it acts as the formula. If your player STILL ISNT convinced by this, it also says on page 14 under Armor Class: “Without armor or a shield, your character’s AC equals 10 + his or her Dexterity modifier.” Which implies its calculated differently with armor and/or shield. Lastly, Entries under armor are listed as a flat number (such as 18 for Plate), while the shield entry says +2, which implies that the Shield AC can be added to an AC calculation, and the Armor can not (and if it could that’s kind of weird being able to wear half plate and make your AC 10+Dex+15+Dex [max 2] AGAIN as opposed to unarmored which only gets to apply dex once. Does wearing armor make you better at dodging…?)
Sorry for the extensive reply, but I’ve encountered a lot of rules lawyers in my time so I want to be thorough.
Hope this helps!
Also feel free to correct me on any of this.
Question about the AC calculation: Does the (for example) AC 15 for half plate already include the base 10 AC, or does that get added onto the 15?
Thanks.
Hi Pink!
Thank you for your question!
When a formula says “Your AC equals”, it overrules any other AC calculation you have, including a creature’s base unarmoured AC (10 + its Dexterity modifier). In other words, while you wear half-plate armour, your AC equals 15, not 25.
Best!
the Archmage
My god, and I thought THACO was complicated. It’s like every class has their own formula. Why is armor+dex bonus+misc. basically being thrown out the window here. I swear, is TSR turned Wizards trying to throw the baby out with the bathwater? How is this supposed to be simpler?
Hi Setsuna,
I’m not sure I get where you’re coming from. It’s so much easier than THAC0. The only thing that people get confused about is that you can’t combine your armour calculations, you take the best one. No dithering with all the situational or sundry modifiers from dodging or deflection, and certainly no touch AC or flat-footed AC, as in Third Edition. And your AC doesn’t constantly go up with your proficiency bonus, like with that edition that shan’t be named. This system is simple and elegant, some people just don’t read the rules very well.
Best,
– the Archmage
It really is all the same formula. Just think about the non-traditional armors (natural/monk/barbarian/etc.) as being a different kind of armor, similar to leather, chain, etc.
Look at the PHB and imagine a section below heavy armor for “Other”, and lizard folk natural armor could be on there as armor AC 13 uses con (instead of dex), and monk unarmored as AC 13 uses dex, barbarian unarmored AC 13 uses con, sorcerer AC 13 uses wisdom, etc. (don’t hold me to correct AC numbers or which attributes, I don’t have the book in front of me).
These alternate formulas, or what I view as alternate armors, allow certain themed characters to keep their theme and stay balanced. Monks don’t have to wear armor and can get into a fight without being immediately cut down due to an extremely low AC. Barbarians, in popular imagery also had little armor, so putting them in plate is kind of odd.
The choice you have to make for the crazy lizard folk monk barbarian is which armor they will use to calculate their AC. They could choose either lizard folk, monk, barbarian OR traditional. Not much different from a fighter choosing between leather, chain, splint, plate, etc. And just like the fighter, they can only choose one.
This ruling official or not does not seem well thought out
“Formulas for calculating AC do not stack” this would make sense if the formulas were complete. They only how the bonus is applied to your AC , implying they are complete would mean the sundry items as you call them don’t add to your AC. Said formulas only show how that one bonus is applied.
Identical bonuses don’t stack , no kidding . A player trying to get the unarmored bonus from a monk and barbarian ether didn’t read the rules right or is trying to pull one over on his GM. Mage armor and Draconic Resilience are not identical , but lets face it , no mater how many different ways you can increase your base AC to 13 it will still only be 13, so they don’t stack. If a GM doesn’t want a sorcerer/monk player he/she should just say so not make excuses
Now lets look at the numbers, is a sorcerer/monk unbalanced , dex 18 wis 18… wait that’s not right a balanced character is one made with the point system the max stat bonus you can have before level 4 is +3 , wow your right a character with unbalanced does result in a character with unbalanced stats. now lets look at what the real numbers would be
AC13 +3(dex) +3(wis) = level 2 AC 19 (band by this ruling) , wow looks big don’t it , you sure about that?
Cleric level 1 AC 16 (chain mail) +2(shield) +/- 0(dex of 8 doesn’t matter with heavy armor) =18 , or not, +2(shield for faith) level 1 AC 20 (still legal) Even if you ignore the spell its still only a one point difference at least 3 classes can start with those stats and you pay for it. First , its very restrictive on how you place your stats. on top of that you are multi-classing , that means even if you only take one level other then your main class , your advancement will always be behind and you will never get your level 20 ability
Hey very nice read thank you. Question: Does the size of the race/creature affect AC at all? I read somewhere that ‘size small’ creatures for example would have 1 higher AC than ‘size medium’ creatures, and that a ‘size large’ creature would have 1 lower AC.
Thank you for your question!
You may have been speaking to someone who is accustomed to earlier editions of D&D. For example, in 3rd edition (the closest mechanically to 5th edition), Small characters had a number of perks: +1 to Armour Class, +1 on attack rolls, and a +4 bonus on Hide checks.
In 5th edition, all racial abilities and perks are presented in chapter 2, “Races”, of the Player’s Handbook. If it’s not there, they don’t have it; that includes bonuses to Armour Class.
To answer your question specifically: No, the size of a creature does not inherently alter their AC in 5th Edition. Making a halfling does not confer an automatic +1 Size bonus to AC, as it did in 3rd, just like making a Large creature (if you were to be permitted to do so) wouldn’t confer an automatic -1.
I thought the Natural Armor replaced the base 10AC for these races, I guess I was wrong. I mean it just seemed like 10 was the Natural Armor for Humanoid base characters based on the wizard, monk and Barbarian AC calculations. Still thank you for the clarification.
Thanks for commenting!
That’s pretty close to what happens. Your base AC goes from being 10 + Dex modifier to, say, 13 + Dex modifier. If it helps, you can treat regular AC as have a natural armour of 10 + Dex modifier; since you don’t count as being armoured while wearing natural armour, there’s functionally no consequence to thinking about it this way.
Just remember that even though you don’t count as wearing armour while benefiting from natural armour, it is a separate method to calculate your AC than the monk or barbarian’s Unarmoured Defence feature and so it they can’t be active at the same time. You can’t be a lizardfolk barbarian who adds their Constitution modifier to their regular AC with natural armour.
Best!
– the Archmage
And that’s the first rule of 5e that I threw right out the window. A Leathery scaled lizardman and squishy Human who are both barbarians or monks with the same stats should NOT have the same AC, and allowing separate calculations for NPCs vs PCs is lazy game design and not consistent with creating rules that apply to the world as a whole.
Thanks for commenting!
If you allow a lizardfolk barbarian with Dexterity 14 and Constitution 18 to stack bonuses and have an AC of 19 at level 1, that’s completely up to you. When your players also multiclass into Draconic Bloodline sorcerer for a second layer of scales, and also into monk for a sixth sense to warn them against danger, and thereby walk around with a flat, say, 24 to AC, then we would love to hear how it impacts your game.
We prefer to use AC as a threshold for when a character must act to avoid, turn away, or otherwise prevent an attack from doing them mortal harm (i.e. lose hit points). Certainly, a barbarian will be better able to withstand physical injury as a result of a supernaturally-thick hide (whether or not it actually corresponds to a physiological change), but a fire-based ranged attack will still burn them, a shocking grasp spell will still electrocute them, et cetera.
AC has been kept deliberately low in 5th edition compared to other editions in order to ensure players do not forget their own mortality. We find that messing with that leads to complications. If you are able to avoid it, then we wish you the best.
One final note we would make about the idea of lizardfolk vs. barbarian toughness that you seem to be hung up on. Try to imagine the meaning behind the numbers. Lizardfolk may have scales, certainly, but a barbarian’s AC bonus is derived from their Constitution modifier, which translates to stamina just as much as it does to hardiness. The lizardfolk barbarian with a Constitution of 16 who uses their natural armour bonus to get an AC of 15 could get exhausted sooner than the human barbarian who has a Constitution of 18 and who uses that to get an AC of 16. With less stamina, the lizardfolk becomes an easier target as the fight goes on, regardless of the superior protection against physical harm offered by his scales.
At least, that’s how we would play it.
When you have to work that hard to explain why something that makes complete sense DOESN’T work that way, then maybe your just messing with numbers arbitrarily in order to enforce a videogame style game balance that makes DMing easier so that you can sell more product. Doesn’t mean the system isn’t functional enough to work with the few changes I would make. A lizard man barbarian, monk SHOULD be able to use his innate toughness, reflexes , barb Stamina training (if that’s the way you choose to explain it) and monk “sixth sense” to be harder to hit than someone without any one of those particular features.. as for stacking a “second layer” of Scales ie. natural AC, well those of use who have played for more than a few years now that same types don’t stack and that’s just fine.
Thank you for commenting!
Once again, when your players decide to multiclass for unarmed AC of 20+ and still benefit from the various abilities that require them to be unarmoured (spellcasting, increased movement, etc.), then we’d be interested to hear how it impacts your game.
Also, Dungeon Master’s Workshop is not affiliated with Wizards of the Coast. We aren’t trying to sell products, we’re simply explaining how the rules work because they’ve been designed a certain way in order that classes are largely on a level playing field.
The various ways of calculating base AC are your armor types. Stacking 2 unarmored types is the same as stacking splint mail and plate mail. They are either or, not accumulative.
If you want to use your monk skill to dodge, use your monk AC. If you want to use your barbarian ability to take the hit (and ignore it) use your barbarian AC.
The underlying math does not support stacking of these armor types any better than it would support stacking splint with plate mail. And, yeah, your various natural and unarmored ACs are just different types of armor, so it would be stacking the same “type”. Putting a lizard man in plate doesn’t stack either… because they are the same type.
I learned something new today. Your footnote about plate and mail was Enlightening. Thank you.
Minor annoyance: it is referred to as plate mail because the warrior wore mail under the plate.
As a medieval historian, I can assure you that “plate mail” is a neologism with no basis in historical useage.
You are correct that mail was worn under plate, but that’s precisely it: mail was always worn under plate, and so when you wore plate there was never any need to include “mail” in the description of your armour.
Just like nobody ever said “chain mail”, because they were the same thing.
Small note: “Plate Mail” or rather “Plated Mail” or “Plate and Mail Armour” is actually a thing although it is more of a description of a type of armour rather than the armour’s formal name…and it is most definitely misused.
It refers to a subset of mail which has the plates built into the structure of the mail rather than being a combination of plate armour worn over the top of mail. Karuta tatami armour and Karuta tatami armour are examples of this style and I believe the style is used in other regions as well but I am less familiar with the non-Japanese styles.