d20 LogoSystem Reference Document v3.5

Unearthed Arcana


In the standard d20 rules, a characterís skill at attacking gets better as he goes up in level ó but not so his skill at avoiding attacks. Characters rely on armor and an ever-growing collection of magic items to protect them in combat. But what about campaigns in which itís not common or appropriate for characters to go everywhere in full plate?

This variant system is particularly appropriate for swashbuckling or stealth-based campaigns, for settings in which firearms are common, for seafaring campaigns (in which the characters would rather not wear armor for fear of drowning), or any other setting in which armor is not worn on a day-to-day basisóeven by adventurers.

Table: Defence Bonus
  1. Use column A for monk, sorcerer, or wizard.
  2. Use column B for bard, ranger or rogue.
  3. Use column C for barbarian or druid.
  4. Use column D for cleric, fighter or paladin.
Using the defense bonus variant in your game means that sometimes, at least, characters wonít want to wear armor ó their defense bonus provides them with free protection thatís just as good as armor. Funds that would otherwise be spent improving a characterís armor can instead be spent on other gear, which means the charactersí power level will increase slightly.

Characters may still desire the properties of a specific kind of magic armor or of armor special abilities. Be prepared to create new magic items, such as cloaks, robes, vests, or vestments, to support those desires.

Clearly, the class defense system is best for characters who must choose between going unarmored and risking arcane spell failure ó sorcerers and wizards in particular. Classes limited to light or medium armor also flourish under this system, since they can multiclass to gain the benefit of a higher defense bonus.

Spells that affect metal are less useful under this system, since metal armor is less common.

Touch attacks are less effective under this system, since most charactersí touch ACs are significantly higher than in a standard game.

In this variant, every character has a defense bonus based on his character level. The defense bonus applies to Armor Class. However, it does not stack with the characterís armor bonus. A character wearing armor gains his armor bonus (including any enhancement to that bonus) or his defense bonus ó whichever is higher ó but not both. The defense bonus stacks with all other bonuses to AC, including the characterís shield bonus, natural armor bonus, and so forth.

Unlike an armor bonus, a defense bonus does improve a characterís AC against touch attacks.

A characterís defense bonus is derived from his character level and class, as shown on Table: Defense Bonus. For a multiclass character, use the highest defense bonus of those offered by the characterís classes. For example, a 2nd-level barbarian has a defense bonus of +4. If the character gains a level of cleric (becoming a 2nd-level barbarian/1st-level cleric), her defense bonus increases to +7, because the clericís +7 at 3rd character level is better than the barbarianís +5 at 3rd character level.

For classes not mentioned here, determine a characterís class defense bonus based on the armor proficiency granted by the class (and only that gained from the class ó you canít take an Armor Proficiency feat to improve your defense bonus). Consult Table: Defense Bonus For Other Classes; the defense bonus progression refers to the indicated column on Table: Defense Bonus. Table: Defence Bonus For Other Classes
Armor ProficiencyDefense Bonus Progression
NoneColumn A
LightColumn B
Light and mediumColumn C
Light, medium, and heavyColumn D
Monsters do not have inherent defense bonuses unless they also have levels in a class or are normally proficient with armor. When calculating a monsterís defense bonus to AC, do not include the monsterís base HD or level adjustment (if any).

For example, a typical green dragon, gargoyle or black pudding has no class levels and is not proficient with any armor. Such creatures do not get a defense bonus.

If a creature is proficient with one or more types of armor, however, it gains a defense bonus. See Table: Creature Defense Bonuses.

If a creature has levels in a class, it gains a defense bonus just like any other character with a class. This bonus does not stack with any defense bonus the creature may have from armor proficiency.

For instance, giants are considered proficient with whatever type of armor (light, medium or heavy) they are described as wearing. Hill giants, described as wearing hide armor, therefore have a +2 defense bonus (hide armor is medium armor). Since this is lower than the +3 bonus of hide armor, the typical hill giant probably prefers to wear his armor. A 1st-level hill giant barbarian, however, would have a defense bonus of +4, and would benefit from discarding his hide armor (though heíd gain a higher armor bonus by putting on chainmail or a breastplate).

Table: Creature Defence Bonuses
Armor ProficiencyDefense Bonus
Light and medium+2
Light, medium and heavy+4


In the abstract d20 combat system, a characterís armor defends him by reducing the chance that an attack will deal damage. That system simplifies the realities of battle in order to streamline combat resolution. An attack that fails due to a characterís armor or natural armor doesnít really fail to connect, but rather fails to connect with enough force to deal any damage. (Thatís why touch attacks ignore a characterís armor and natural armor ó the touch attack only needs to connect to deliver its effect, and need not actually breach the targetís armor.)

If youíre willing to add a layer of complexity to your combats, consider this variant. In this system, armor reduces the amount of damage dealt by an attack instead of merely turning would-be hits into misses. Armor still prevents some hits outright, but also reduces the deadliness of attacks that do connect. In essence, the system "gives up" some of armorís ability to turn hits into misses in exchange for a small reduction in damage dealt by any given attack.

In this system, armor offers two benefits against attacks: a minor bonus to AC, which functions just like the armor bonus in the standard d20 rules but is usually lower in value; and damage reduction. See Table: Armor and Damage Reduction for the armor bonus and DR values for common armor types. (All other armor statistics, such as maximum Dexterity bonus, armor check penalty, and arcane spell failure chance, are unchanged.)

For armors not covered on Table: Armor and Damage Reduction, you can determine the new armor values and damage reduction based on the standard armor bonus. To determine the armorís damage reduction, divide the armorís normal armor bonus by 2 (rounding down). To determine the armorís new armor bonus, subtract the DR from the normal armor bonus. For example, studded leather has a normal armor bonus of +3. That gives it a DR of 1/- (half of 3, rounded down) and a new armor bonus of +2 (3 minus 1).

Table: Armor and Damage Reduction
ArmorArmor Bonus1Damage Reduction
  1. Add any enhancement bonus to this value.
Light armor
Studded leather+21/-
Chain shirt+22/-
Medium armor
Scale mail+22/-
Heavy armor
Splint mail+33/-
Banded mail+33/-
Full plate+44/-
An armorís enhancement bonus (if any) increases its armor bonus to AC, but has no effect on the armorís damage reduction. A +3 chain shirt, for example, adds +5 to AC and grants damage reduction 2/-.
The damage reduction granted by armor stacks with other damage reduction of the same type (that is, damage reduction that has a dash after the number). A 7th-level barbarian wearing a breastplate has DR 3/- (1/- from his class levels and 2/- from his armor). A fighter wearing full plate armor who is the target of a stoneskin spell, however, has DR 4/- from the armor and 10/adamantine from the spell.
Shields function normally in this variant, granting their full shield bonus to AC. Unlike with armor, a shieldís effectiveness is measured wholly by its ability to keep an attack from connecting with your body.
A creatureís natural armor also provides a modicum of damage reduction. Divide the monsterís natural armor bonus (not including any enhancement bonus) by 5 to determine the monsterís damage reduction. The same value is subtracted from the monsterís natural armor bonus to find the monsterís new AC. These calculations are summarized in Table: Natural Armor and Damage Reduction.

If the creature already has damage reduction, either add the value gained from natural armor (if the existing damage reduction is of the same type) or treat it as a separate DR value (if it is of a different type).

For example, a mummy normally has a natural armor bonus of +10. This gives it DR 2/-, and its natural armor bonus is reduced by 2 points to +8 (making itís AC 18). Since the mummy already has DR 5/- as a special quality, its total damage reduction becomes DR 7/-.

A mature adult red dragon has a natural armor bonus of +24. This gives it DR 4/-, and its natural armor bonus is reduced by 4 points to +20 (making its AC 28). The dragonís existing damage reduction is 10/magic, so the two damage reduction values remain separate.

Finally, a frost giant has a +9 natural armor bonus, so it gains DR 1/- from natural armor. The chain shirt it wears gives it an additional DR 2/-. If the frost giant were a 7th-level barbarian, the barbarian class levels would give it DR 1/-. These three values add up to DR 4/-. The giantís AC would be 20 (10, +8 natural armor bonus, +2 chain shirt).

Table: Natural Armor and Damage Reduction
Natural Armor BonusDamage ReductionSubtract from Natural Armor
Itís pretty easy to see the effect of this variant system: attacks hit more often, but do less damage. What does that really mean?

Low-level combat tends to be less dangerous for armored characters. Although their ACs are lower (and thus their chance of being damaged is higher), this is more than offset by the reduced damage suffered by attacks. A typical goblin warrior, for instance, can barely hurt a character wearing splint mail, because the armorís damage reduction entirely negates the damage dealt by an average hit. Even though the goblin will hit more often, it will likely end up dealing less total damage over the course of a typical battle.

A mid-level fighter in full plate armor must still be cautious when fighting an ogre, but his armor reduces the ogreís average damage by 25% while only increasing its chance to hit by 20% ó a net gain for the fighter.

At higher levels, however, the balance shifts back in favor of monsters that deal large amounts of damage per hit. When facing a Huge earth elemental, a fighter in full plate will be hit 20% more often (due to the 4-point reduction in AC), but his 4 points of damage reduction now only reduces his opponentís average damage by less than 17%. Advantage: elemental. Thus, high-level characters must be more careful when battling monsters with extreme damage-dealing capability.

You can combine the defense bonus variant and the armor as damage reduction variant in a variety of ways to create a more complex system.

Using both systems as written, many characters will wear armor even if the armor bonus provided is lower than the defense bonus gained from class level. Because the character gets the higher of his defense bonus or armor bonus, the character can wear armor and benefit from its damage reduction while relying on his defense bonus for a higher Armor Class.

If thatís not to your liking, you can rule that a characterís armor bonus overrides his defense bonus, even if the defense bonus is higher. This forces characters to make a tough choice between having a high AC and having damage reduction.


In the standard d20 rules, armor reduces the chance of a character taking damage in combatóbut thatís the limit of its protection. In this variant, armor not only protects in that manner, but also turns fatal blows into less-threatening hits. Armored characters are often more easily battered into unconsciousness than brought down by lethal damage. Itís a system that works well in campaigns with a great deal of combat between armored foes, but in which magical healing is not common. Itís also ideal in a world where ethical or legal standards dictate that subduing or capturing opponents is preferable to killing them.
Armor, in addition to adding a bonus to AC, also converts lethal damage from physical attacks into nonlethal damage. (Shields provide a shield bonus to AC, as normal, but do not convert damage.)

Each time an armor-wearing character is struck by an attack that deals lethal damage, the amount of damage dealt to the character is reduced by an amount equal to the armor bonus (including enhancement) of the armor worn. The character takes and equal amount of nonlethal damage. Damage that is not affected by damage reduction (energy damage and the like) is not converted.

For example, while wearing +1 full plate (total armor bonus +9), Kroh is struck by an arrow for 6 points of damage. Since the armor can convert up to 9 points of damage per attack, the entire 6 points is converted from lethal damage to nonlethal damage. Krohís hit point total remains the same, but he increases his nonlethal damage total by 6 points. Later, a hill giant strikes Kroh for a whopping 22 points of damage. The armor converts 9 points of this damage to nonlethal damage, but the remaining 13 points are deducted from Krohís hit points.

Nonlethal Damage: An armor-wearing character can ignore nonlethal damage equal to his armor bonus. (In effect, armor grants damage reduction equal to its armor bonus against nonlethal attacks.)

Natural Armor: At your option, you can make natural armor work in the same manner. However, this means that almost no defeated monster is truly dead, which may prove problematic (see Behind The Curtain: Damage Conversion). This rule also interacts strangely with regeneration ó since all damage dealt to a creature with regeneration is treated as nonlethal damage, a regenerating creature with armor or natural armor actually takes less damage than normal when using this system. In case of regenerating creatures, consider eliminating the rule that natural armor works in the same manner.

With this system, a character still takes as much damage from a hit as in the normal combat rules. Barring any magical healing delivered during the fight, a battle lasts just as long as in a standard game. Since nonlethal damage goes away faster than lethal damage, though, characters can recuperate from their battles relatively quickly, even without magical healing, making this variant ideal for low-magic campaigns.

However, healing spells become potentially doubly effective, since they heal an equal amount of lethal and nonlethal damage.

Nonlethal attacks become less frightening to armored opponents. A fighter in full plate simply has no fear of unarmed opponents, since they have little chance of injuring him. (Of course, they can still overrun, trip, or grapple him, so heíd be wise to keep and eye on them all the same.)

Another effect is that defeated foes remain alive (and unconscious) unless dispatched after the fight. This can decrease character mortality dramatically ó since most characters who fall in battle will be merely unconscious, but not dying ó but it also introduces the potentially ugly postcombat scene of the characters feeling it necessary to slit the throats of their unconscious foes. Some characters, particulary paladins or other chivalrous types, may suffer serious moral qualms.

This variant is probably best for campaigns in which itís acceptable for the bad guys to survive a fight. Perhaps a defeated villainís honor prevents him from returning to plague the heroes at a later date, or maybe the style of your setting rewards characters for defeating opponents without killing them outright (such as in a swashbuckling campaign). Otherwise, characters may feel that they are punished for refusing to murder unconscious foes with regularity, since those enemies will certainly recover from their injuries and vow vengeance against the PCs. Encounters in the campaign may often involve fighting the same opponents again and again, rather than fighting new monsters and opponents.