Armor and Damage Reduction

In the abstract d20 combat system, a character’s 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 character’s armor or natural armor doesn’t really fail to connect, but rather fails to connect with enough force to deal any damage. (That’s why touch attacks ignore a character’s armor and natural armor — the touch attack only needs to connect to deliver its effect, and need not actually breach the target’s armor.)

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 armor’s 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. All other armor statistics, such as maximum Dexterity bonus, armor check penalty, and arcane spell failure chance, are unchanged.

You can determine the new armor values and damage reduction based on the standard armor bonus. To determine the armor’s damage reduction, divide the armor’s normal armor bonus by 2 (rounding down). To determine the armor’s 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/Adamantine (half of 3, rounded down) and a new armor bonus of +2 (3 minus 1). Heavy armors work the same, except the DR they give is /- rather than /Adamantine.


An armor’s enhancement bonus (if any) increases its armor bonus to AC, but has no effect on the armor’s damage reduction. A +3 chain shirt, for example, adds +5 to AC and grants damage reduction 2/Adamantine.


The damage reduction granted by armor stacks with other damage reduction of the same type (that is, damage reduction that has Adamantine or a dash after the number). A 7th-level barbarian wearing a breastplate has DR 1/- and DR 3/Adamantine (1/- from his class levels and 3/Adamantine from his armor). A fighter wearing a breatplate who is the target of a stoneskin spell, however, has DR 13/Adamantine (3/Adamantine 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 shield’s effectiveness is measured wholly by its ability to keep an attack from connecting with your body.


A creature’s natural armor also provides a modicum of damage reduction. Divide the monster’s natural armor bonus (not including any enhancement bonus) by 5 to determine the monster’s damage reduction. The same value is subtracted from the monster’s natural armor bonus to find the monster’s new AC. Monster DR is /-.

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 it’s 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 dragon’s existing damage reduction is 10/magic, so the two damage reduction values remain separate.

Armor and Damage Reduction

Caught Between Worlds Lord_Entropy