Damage Conversion

I'm using the suggested alternative rules from Unearthed Arcana (p112) to emulate a slightly more realistic way to use armour, with a couple of changes.

Damage Conversion Rules

• Each point of AC (excl. shields, incl. enhancement & natural) count as 1 point of damage reduction for physical damage.
• Each point absorbed by the armour is taken as non-lethal damage.
  • Nonlethal damage acquired in this manner is not ignored by regenerating creatures but applied like how lethal damage would have been applied otherwise (in essence: the two buffs do not stack).

In short: Any AC bonuses and Natural Armor bonus a character has will convert that amount of lethal damage into nonlethal damage, making well armoured characters more prone to survival, but also being knocked out.

The main effect is that the opponent need to decide on killing the unconscious foe after the blood has stopped boiling rather than killing him in the fray of battle.

Damage Conversion in Unearthed Arcana

This is added for reference. A short excerpt from Unearthed Arcana (page 122).

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 an 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), Tordek 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. Tordek’s hit point total remains the same, but he increases his nonlethal damage total by 6 points. Later, a hill giant strikes Tordek 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 Tordek’s 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 the Behind the Curtain sidebar). This rule also interacts strangely with regeneration—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 the case of regenerating creatures, consider eliminating the rule that natural armor works in the same manner.