I want to teach the game to some new player, and while doing homemade character sheets, for simplicity, I wanted to use the term "Defense" instead of "Armor class" (which I found a bit unintuitive).

Is there some reason at start to not just called it Armor Class?

I couldn't find any use of the word "Defense" or "Defence" alone in the game, and we already use the simple term attack, so why not?

PS: note that I'm French, perhaps the term is more commonly used in English language, that in French, which was translated literally as "Classe d'Armure"

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    \$\begingroup\$ It may be worth noting that in the English rules, the analogy to "Armor Class" is not "Attack", but "To-Hit Bonus"; "Attack" does indeed already exists, as an action. \$\endgroup\$
    – goodguy5
    Commented Jan 9, 2020 at 13:35
  • \$\begingroup\$ Wasn't ArmorClass "invented" to circumvent the little illogical point that lower ArmorClass actually meant better defense ? \$\endgroup\$
    – eagle275
    Commented Jan 10, 2020 at 9:17
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    \$\begingroup\$ A player has many different types of defenses. For example, each saving throw is a form of defense. Calling it defense would not be appropriate. \$\endgroup\$
    – ikegami
    Commented Jan 10, 2020 at 16:27
  • \$\begingroup\$ Class, comme classification, comme "rating". \$\endgroup\$
    – ikegami
    Commented Jan 10, 2020 at 16:27

2 Answers 2


Armor Class is a type of Difficulty Class

In Dungeons & Dragons 5e (and previous editions too if I'm not mistaken), usually the way to see if you are successful at doing something is to roll a d20, add relevant bonuses, and see if it matches the number you need to succeed. The number you need to succeed is called the Difficulty Class. This is true for skill checks, saving throws, and attack rolls.

The difficulty class you need to meet for attack rolls is called the Armor Class because usually, for player characters, the main way to determine this number is based on what armor they are wearing.

QuadraticWizard's answer has some great history but I think this common sense answer will help your new player understand D&D better.

  • \$\begingroup\$ I agree with most of this answer, but I disagree with the usage of "usually". Many many characters include Dexterity bonuses in their armor class, with light armor characters often getting a larger bonus from Dex than from armor. \$\endgroup\$
    – Taejang
    Commented Mar 27, 2023 at 22:16
  • \$\begingroup\$ @Taejang I meant at least in part "based on what armor they are wearing", not solely. The exceptions I was thinking of are things like the Monk or Barbarian's Unarmored Defense, Natural Armor, or just the base AC of 10+DEX. \$\endgroup\$
    – Nacht
    Commented Aug 14, 2023 at 3:06

It derives from the wargames which inspired D&D.

The 1971 Chainmail miniatures game which inspired D&D included a table for one-on-one combat, which determined hit or miss based on the attacker's weapon and defender's armor. This appears to be the origin of D&D's term "armor class", which referenced the Chainmail rules. The meaning appears to be similar to "classification", as in how to sort, rank, or group different things.

The term "class" is widely used throughout the Chainmail rules to refer to a category, group, ranking, classification, or type of things, including weapons, armor, cannons, heroes, wizards, elementals, and undead. "Class" is similarly used in the wargame Don't Give Up the Ship, where it is used to categorize different ships based on tonnage. This may have been a common naming convention in among wargamers in the 1970s.

The man-to-man combat rules in Chainmail provide a table to determine the roll required to hit, which takes into account weapon type vs armor type. Some armor types share a column in the melee table; e.g. leather and padded armor are functionally the same. The ranged weapon table refers to "Class of armor worn by the defender", giving a number to each of eight armor groups.

The original 1974 Dungeons & Dragons provides an alternative combat system which closely matches the Chainmail table, except that the number is now referred to specifically as "Armor Class", and it is higher level rather than weapon type which determines the number which must be rolled to score a hit.

Originally, then, "armor class" simply meant "type of armor worn", with the implication that some armor is better than others. Since most monsters do not wear armor, and there are other magical means of increasing armor class in D&D, the term "armor class" soon became decoupled from the actual armor types, and referred only to the to-hit number. However, it was retained largely out of D&D tradition, which has always kept a lot of archaic words and ideas as part of its flavor.

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    \$\begingroup\$ @TedPwyll It may confuse players when they read the Player's Handbook or another D&D book. For example, if they find a spell which increases "armor class", they may be confused if they don't know that term. They may also eventually join a D&D group which uses the official term "armor class", or may ask a question here on this site, and it will be helpful to know the official terminology. \$\endgroup\$ Commented Jan 9, 2020 at 13:42
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    \$\begingroup\$ Very interesting! The natural follow-up question is how come AC hasn't been replaced by 'Defense' in the later versions which is way more intuitive? \$\endgroup\$
    – Aventinus
    Commented Jan 9, 2020 at 13:44
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    \$\begingroup\$ @Aventinus the only objective definition of "intuitive" is "expected by, and familiar to majority of your target audience". In cases of the D&D majority = players of the previous editions, so you may be mistaken of what really is intuitive. \$\endgroup\$
    – Mołot
    Commented Jan 9, 2020 at 13:49
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    \$\begingroup\$ Also worth pointing out that when you make an ability check or saving throw, you do so against a "Difficulty class". Which corresponds to an attack roll against an "Armor class". Nice and consistent. You could, of course, change AC to "Defense", but then you would also need to change DC to....something similar?....otherwise you're just multiplying the terms that players would need to know. AC and DC have a nice correspondence! \$\endgroup\$
    – PJRZ
    Commented Jan 9, 2020 at 13:56
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    \$\begingroup\$ It might be worth mentioning that in the D20-derived Star Wars RPGs, they actually did call it "Defense". \$\endgroup\$
    – T.J.L.
    Commented Jan 9, 2020 at 18:56

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