Armor and Damage Redux (5e Variant Rule)
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Armor as Scaling DR
This variant allows for armor to affect the damage you take from attacks without the problem of armor becoming useless at higher levels, or low-damage attacks being useless against heavy armor. This variant also takes into account the real fact that weapons technology exists in order to bypass armor, and armor technology exists to protect against better weapons.
In this variant, first note the following characteristics:
Your attack roll with melee weapons uses Str, unless it has the finesse property, in which case it can use Dex instead if you so choose. Ranged attacks always use Dex, but if it has the thrown property, you may use Str if you so choose.
When you make an attack roll, you target a value called Combat Defense, which takes the place of what AC was. This is determined as follows:
-If you are wearing light or no armor, it is 10 + Dex bonus, and you add your proficiency bonus if you are proficient in light armor, or if you have Unarmored Defense and you are not armored.
-If you are wearing medium armor, it is 10 + Dex bonus, with a maximum Dex bonus of +2, and you add your proficiency bonus if you are proficient in medium armor.
-If you are wearing heavy armor, it is 10, and you add your proficiency bonus if you are proficient in heavy armor.
-If you are holding a shield, you add +2.
In other words: CD = 10 + Dex bonus (max +2 with medium, none with heavy) + proficiency bonus if applicable + shield bonus
Armor Class (AC) is a new value which affects damage taken. It is calculated as follows:
Your armor's Base AC minus 5 is your Base AC for this variant.
Damage reduction is reinterpreted as follows: If you have damage reduction, divide the number by 5 and add it to your AC.
When rolling damage rolls with a weapon, add your proficiency bonus to the damage roll. Do not add your proficiency to spell damage.
Your hit points are calculated as follows:
Your class's average hit die (e.g. 5 for a 1d8 hit die, 6 for 1d10, etc.) + your CON mod once + 1 for every level above first
If you get extra hit points from special effects, divide the number by 5. Barbarians have the following additional class feature:
Barbarian resilience: You increase your hp by 1 for every barbarian level you have. When you heal during a short rest, you heal 2 hp instead of 1 hp.
Monster hp: Take the average result of the dice and divide by 5. You can try to recreate the effects of random hp by rolling all the hit dice and dividing by 5.
Damage from an attack that affects AC in the regular rules: If the damage is less than your AC, you take no damage, but the attack still hits. Any effect that applies to an attack that hits applies, but an effect that applies to an attack that deals damage does not apply. If the damage is equal to or higher than your AC, but less than twice your AC, you take 1 hp loss.
This is usually simple enough to deal with in combat, so the complicated calculation of the following rule isn't going to come up all the time:
For every amount equal to your AC higher than your AC, add 1 hp loss. For example, if it is twice your AC, take 2 hp loss. If it is three times your AC, take 3 hp loss. Another way of thinking about it, if you're up to doing math instead of counting: your hp loss is damage divided by AC.
Critical hits, resistance, vulnerability, sneak attack, and all the other effects apply the same way to damage (the dice you roll from your weapon), not hp loss.
Damage from an attack that does not affect AC in the regular rules: Divide the damage by 5 (or treat it like AC 5). You can call this number (5) "toughness" or "special AC" or whatever you like. If you have DR, divide the DR by 5 and add it to this number.
Healing: Healing affects your hp. For a straight number of hp healed, divide the number by 5. If you are healing with dice, divide the average result by 5. When healing using hit dice during a short rest, heal 1 + your Con mod (minimum 1), or 2 + Con mod if you are a barbarian.
Unarmed strike: Unarmed strike deals 1d4 damage plus your Str mod, or 1d6 + Str mod if you are attacking with a hard shoe or gauntlet. A monk's martial arts does not apply to an attack made with a shoe or gauntlet, and these articles are not monk weapons.
With this variant, hp roughly reflects the number of weapon attacks you can take before going down, on average. Combat should, at least at lower levels, last a number of turns equal to the total hp of the monsters, if every attack hits. Critical hits, sneak attack, and spells with quicken things up.
NOTE: If you use this variant, you cannot win by attrition. Low-damage attacks cannot pile up on an enemy to do more damage. This isn't necessarily a problem, but if you would like to allow for this possibility, consider the following variant variant (this will make things more complicated):
-If you have advantage on an attack, you also have advantage on damage (roll one of the damage dice twice, choosing which result to take). This does not apply to disadvantage.
-Whenever you hit with an melee or ranged weapon (whether it causes hp loss or not), all attacks with melee or ranged weapons, deal an extra die of damage until the start of your next turn. This can only apply once at a time. If multiple people attack, or one person attacks twice, the extra die is still only 1.
-Alternative to the previous: if you attack more than once in the same round, such as with the Extra Attack feature, make separate attack rolls, but combine the damage rolls together. You roll all the damage of the same type from the attacks you made during your turn at the end of your turn.