Armor As Dr

Variant Rules

The standard armor system abstracts protection as a reduced chance of being hit, which can feel unintuitive — if a breastplate is actually deflecting blows, why does it make you harder to hit rather than harder to hurt? This variant answers that question directly: armor no longer raises Armor Class; instead it absorbs damage after a hit lands. A creature becomes easier to strike but significantly harder to injure, and armor quality determines how much punishment it soaks.

Optional Rule. This system replaces the standard armor and AC rules entirely. Adopt it for all creatures or only for PCs — the GM decides scope at session zero. DR from this system stacks with all other forms of DR.

Defense

Creatures no longer have an Armor Class. Instead each creature has a Defense score — analogous to touch AC — that an attacker's roll must meet or exceed. The armor bonus and natural armor bonus are removed from this calculation; they become DR instead (see below).

Defense = 10 + shield bonus + Dexterity modifier + other modifiers
(includes armor's enhancement bonus; excludes armor bonus and natural armor bonus)

The shield bonus is included because a creature actively interposes its shield whenever it retains its Dexterity bonus. Enhancement bonuses to armor still apply to Defense, since they represent magical reinforcement that helps the armor deflect blows.

Losing Dexterity Bonus to Defense

Any situation that would strip your Dexterity bonus to AC also removes your Dexterity bonus to Defense — and simultaneously removes your shield bonus, since you can no longer react to attacks quickly enough to use the shield effectively.

Flat-Footed Defense

Flat-Footed Defense = Defense − Dexterity modifier − shield bonus. When you use a shield you are not proficient with, take the shield's armor check penalty as a penalty to your shield bonus — this also reduces your Flat-Footed Defense, as the shield impedes rather than protects.

Armor as Damage Reduction

A creature's armor bonus (plus any enhancement bonus to the armor bonus, plus natural armor bonus) converts directly into DR/armor. Creatures proficient with their armor also gain a scaling bonus to that DR as they gain levels or Hit Dice.

DR Bonus by Level / Hit Dice (proficient wearers only)
Level or HD	Bonus to DR
1st – 4th	+0
5th – 9th	+1
10th – 14th	+2
15th – 19th	+3
20th+	+4 (maximum)

Creatures using armor they are not proficient with do not gain this per-level bonus (in addition to the standard non-proficiency penalties).

DR/Armor — Bypassing the DR

DR/armor blocks damage from all attacks normally subject to DR. Its type — what bypasses it — is determined by the armor's material and whether it is magical. Unlike most DR, DR/armor stacks with other forms of DR.

Example: A skeleton with DR 5/bludgeoning wearing +2 chain mail has DR 4/armor (6 armor bonus + 2 enhancement, but capped here for illustration). Against a non-bludgeoning attacker the skeleton reduces 9 damage (5 + 4); against bludgeoning the DR/armor still applies but the DR 5/bludgeoning does not.

Table: Armor Composition and DR
Material	DR Provided	Attacker Size to Bypass DR
Nonmagical armor	DR/magic	Large
Magical armor	DR/adamantine	Huge
Adamantine armor	DR/—	Gargantuan
Brilliant energy weapons bypass any DR from armor. DR/armor is halved when the wearer is grappled or entangled, and does not apply when the wearer is helpless or pinned.

Natural Armor Bonus and DR

A creature's natural armor bonus is also converted to DR/armor and added directly to the armor bonus for purposes of total DR. A creature wearing a +2 chain shirt (DR 6/armor) that gains a barkskin +3 bonus has DR 9/armor for the spell's duration.

When a creature has both natural armor and DR from another source, it gains an enhanced form of DR/armor — take the best protection provided by either the armor's composition or the interaction of natural armor and existing DR (see table below).

Table: Natural Armor Conversion to DR
Natural Armor + Existing DR	DR/Armor Provided	Attacker Size to Bypass DR
Natural armor + DR/magic	DR/adamantine	Huge
Natural armor + DR/adamantine	DR/—	Gargantuan
Natural armor + DR/—	DR/— ¹	Colossal
Natural armor + DR/epic	DR/epic ¹	n/a
¹ A creature that already has DR/— or DR/epic increases its DR by an amount equal to its natural armor bonus.

Unusual Creatures and Armor DR

Amorphous and incorporeal creatures have an easier time penetrating DR/armor. Incorporeal attacks ignore it entirely unless the DR comes from a force effect or ghost touch armor.

Table: Unusual Creatures and Armor DR
Attacking Creature Type	DR Modifier
Amorphous ¹	×½
Incorporeal	×0 (×1 if DR is from force effect or ghost touch armor)
Swarm of Tiny creatures	×½
Swarm of Diminutive creatures	×¼
Swarm of Fine creatures	×0
¹ Includes elementals, oozes, ooze-like creatures, and any creature with the amorphous defensive ability.

Critical Hits and Defense

When an attacker threatens a critical hit, there is no confirmation roll. Instead, the target makes a critical defense check to reduce the critical hit to a normal hit. This replaces the standard confirmation mechanic entirely.

Critical Defense Check Bonus

creature's DR
+ Dexterity modifier (max armor's Dex cap)
+ shield bonus to Defense
+ deflection bonus

Critical Defense DC

critical threat roll
+ ½ attacker's base attack bonus
+ 1 per critical feat (max 10)
+ 1 per size category larger than target

On a successful check, the critical hit is reduced to a normal hit and damage is reduced by the target's DR as usual. On a failed check, the critical hit stands — and its damage is still reduced by DR.

Example: A Medium 6th-level fighter with two critical feats fires a crossbow; the critical threat roll is a 19. Critical defense DC = 19 + 3 (½ BAB) + 2 (feats) = 24. The Medium target wearing +1 leather armor, with Dex 18 and a +1 buckler, has: DR 3 + 4 (Dex) + 1 (shield) + 1 (enhance) = +9 bonus. On a roll of 15+, the critical is reduced to a normal hit.

Fortification. The fortification special armor quality interacts with the critical defense check: if the check fails, fortification still has a chance to negate the critical, functioning as normal.