Instead of having a single value determine whether (1) you are hit and (2) you shrug off the attack, this system separates this into two separate values.
Dodge and Damage Reduction
Dodge. Your AC becomes your Dodge. Any attack roll that is lower than your AC/Dodge has no effect. Any attack roll that is equal to or higher than your AC/Dodge hits you. Your AC/Dodge is equal to 10 + your Dexterity modifier+ your proficiency bonus - your armour's encumbrance. If you are wearing a shield, its bonus is added to your AC/Dodge. Fighting styles and similar abilities that normally increase your AC are still added to your AC/Dodge.
Armour and Damage Reduction. Wearing armour lets you reduce incoming damage at the cost of lowering your AC/Dodge. Your armour's encumbrance is detracted from your AC/Dodge. When you take damage from a an attack, or a saving throw against a weapon-like effect, you reduce that damage by your armour's damage reduction (except from psychic or poison damage, and ethereal attacks by ghosts etc.). The reduction from DR occurs after damage is halved or doubled by features such as resistence or vulnerability.
To determine your encumbrance and DR consult the table below.
Critical Hits. Critical hits on attack rolls bypass damage reduction.
Armour Table
Armour Type | Damage Reduction | Encumbrance (AC modifier) | Special |
|---|---|---|---|
Light armour | |||
Padded | 1 DR | -1 | Lightweight |
Leather | 1 DR | -1 | |
Studded Leather | 2 DR | -2 | |
Medium Armour | |||
Hide | 3 DR | -2 | |
Chain Shirt | 3 DR | -1 | Str 10 |
Scale Mail | 4 DR | -2 | Clunky |
Breastplate | 5 DR | -3 | |
Half Plate | 7 DR | -4 | Clunky |
Heavy Armour | |||
Ring Mail | 5 DR | -3 | |
Chain Mail | 6 DR | -3 | Clunky / Str 13 |
Splint Mail | 8 DR | -4 | Clunky / Str 15 |
Plate | 10 DR | -5 | Clunky / Str 17 |
Other Defences | |||
Shield | +2 | ||
Mage Armour, spell | 3 DR | ||
Barkskin, spell | 6 DR | ||
Barbarian Unarmoured Def. | DR = CON mod. | ||
Monk Unarmoured Def. | + WIS mod. | ||
Lightweight. You can wear this armour without having the necessary armour proficiency. However, if you are not proficient with this armour, Concentration checks are made at disadvantage.
Clunky. While wearing this armour, you have disadvantage on Dexterity checks.
Strength Requirement. Some armours require a minimum Strength score to be used properly. If your Strength score is less than this total, your movement speed is reduced by 10 feet.
Magical Armour. Any armour that has the +1, +2, +3 etc. magical property gain this bonus to both DR and Encumbrance. The bonus to Encumbrance can however not go beyond 0. For example, a +2 Plate has 12 DR and -3 Encumbrance and a +3 Leather has 4 DR and only 0 Encumbrance. Some armours may have a bonus only to AC/Dodge, DR, or Encumbrance.
Mithril. Mithril armours are lightweight reducing their Encumbrance by 1. For example, a Mithril Breastplate has an Encumbrance of -2 instead of -3.
Note that the Defence fighting style increases AC/Dodge by 1, and Heavy Armour Master increases DR by 3.
Examples and Considerations
This system changes the game in certain ways.
What does dodging and armour mean to me? Dodging becomes the way you avoid attacks, while armour lets you reduce the damage you take if you are hit. You can choose to focus on dodging, which means you'll take damage less often, but, when you do, it'll hit you harder. Focusing on armour on the other hand means you'll take damage more often but less each time.
Fighting heavy hitters. With this system, enemies that have few but very strong attacks do more damage to those wearing armour. This is because they concentrate all their damage into one or two attacks, meaning your DR only comes into effect one or two times. If the enemy deals 50 damage over two attacks and you have a DR of 5, you'll reduce the damage you take by 5*2=10. When fighting a single heavy hitter, you may want to shed your armour to instead dodge their attacks.
Death by a thousand cuts, or not. With this system, enemies that have many attacks which individually are not very strong will do less damage to those wearing armour. This is because each attack will deal a medium to low amount of damage, each of which will be reduced by your DR. If the enemy deals 50 damage over five attacks and you have a DR of 5, you'll reduce the damage by 5*5=25. When fighting an enemy with a lot of attacks, or a horde of enemies, you may want to armour up.
Monsters and NPCs
Most humanoid NPCs can utilise this system when determining their Dodge and DR.
Some monsters, however, have naturally high AC without wearing armour. When determining their Dodge and DR, you can use their AC as a starting point. The AC of a monster is a result of their natural ability to dodge attacks and their natural defences' ability to prevent harm. In general, their DR equals AC - DEX mod - 10, and their Dodge equals 10 + DEX mod + PB.
For example, an Adult Gold Dragon has an AC of 19, a DEX mod of +2, and a Proficiency Bonus of 6. The damage reduction of its scales will be 19 - 2 - 10 = 7. Its dodge will be 10 +2 + 6 = 18. Meanwhile a Troll has an AC of 15, a DEX mod of +1, and a PB of +3. Therefore, its DR is 15 - 1 - 10 = 4 and its Dodge is 10 +1 + 3 = 14.