D&D 5E Alternate AC calculation

[Joel Spanky Gray]

So here is a more complex AC calculation method that I've used for a few months. For anyone that has ever sparred with hand weapons you know that being armed with any medium length hand weapon increases your defense, and that shields are underrated, but lose a little of their effectiveness when wearing heavy armor. So here is an AC patch you can use, and please feel free to make some suggestions on how I could make it even better.

First, I split AC into Melee AC and Ranged AC.

MELEE AC = 8 + Mobility bonus + Armor bonus

Mobility bonus = [Dexterity modifier + Proficiency bonus]/2, round up.
- Monks add their Wisdom modifier to their mobility bonus.

Armor Bonus = Take the highest bonus as a base, then add 1/2 of the other bonuses (round up).
- Armor bonus is 1 (thick clothes), 2 (padded/leather), 3 (hide, studded leather), 4 (scale, chain), 5 (brigandine, heavy chain, light plate), 6 (plate), 7 (heavy plate).
- Shield bonus is 2 (small), 4 (medium), 6 (large).
- Weapon bonus is 0 (short - dagger, short club), 1 (most one-handed weapons), 2 (most two-handed weapons), 3 (reach weapons like polearms and long spears)
- Barbarians use their Constitution modifier instead of Armor bonus if it is higher.

RANGED AC = 8 + Mobility bonus + Armor bonus
- The same as Melee AC, but do not use weapon bonus. Ranged AC tends to be a little lower than Melee AC.

I never bothered with distinguishing light/medium/heavy armor. That is completely relative to Strength. Although I do use the disadvantage on Stealth part. I only recalculate the AC of humanoid monsters that use weapons, shields, and armor.

 

[Raith5]

Interesting. Does an axe really give you a parrying benefit IRL? But I like the idea that different weapons could give different kinds of benefits. I can see a long sword giving a defensive bonus (I am not sure about two handed weapons - they seem kind of wide open on defense) but I could see an axe as having some further offensive bonus.

 

[Horwath]

Interesting. Does an axe really give you a parrying benefit IRL? But I like the idea that different weapons could give different kinds of benefits. I can see a long sword giving a defensive bonus (I am not sure about two handed weapons - they seem kind of wide open on defense) but I could see an axe as having some further offensive bonus.

Two handed weapons are not open to defense. I can tell you that from HEMA training.

Point of being armed is that opponent cannot make all the attacks he can think of as he is going to get impaled on your sword.

And as a longsword(dnd greatsword) is long , you can block a lot of angles of attack with it(melee ofc).

Axes usually had "langets":


thin metal strips along the handle to make it more durable at blocking sharp blades.

more or less anything in your hands is better at blocking the weapon than your hands.

Even cloak wrapped few times over forearm can be improvised shield against light/not so sharp blades in a hurry.

 

[Joel Spanky Gray]

Point of being armed is that opponent cannot make all the attacks he can think of as he is going to get impaled on your sword.
And as a longsword(dnd greatsword) is long , you can block a lot of angles of attack with it(melee ofc).
Axes usually had "langets":
thin metal strips along the handle to make it more durable at blocking sharp blades.
more or less anything in your hands is better at blocking the weapon than your hands.
Even cloak wrapped few times over forearm can be improvised shield against light/not so sharp blades in a hurry.

This ^ and anything that keep your enemy at a distance helps your defense by giving you extra time to react. I could even see it argued in my system that certain weapons, such as spears, quarterstaffs, and polearms may even get a +4 weapon bonus instead of +3. I haven't crunched the numbers but I wanted a system where the highest AC was similar to the RAW.

Example #1) 6th-level Fighter (+3 proficiency) with Dex 12 (+1), wearing heavy plate (+7), and a halberd (+3) has Melee AC 19, Ranged AC 17.
Example #2) 5th-level Rogue (+3 proficiency) with Dex 17 (+3) wearing leather (+2), and a rapier (+2) has Melee AC 14, Ranged AC 13.
Example #3) 10th-level Ranger (+4 proficiency) with Dex 16 (+3) wearing studded leather (+3) and a bow (0) has Melee AC 15, Ranged AC 15.
Example #4) 10th-level Fighter (+4 proficiency) with Dex 12 (+1) wearing heavy plate (+7), large [kite] shield (+6), and a longsword (+2), has Melee AC 22, Ranged AC 21.

 

[Joel Spanky Gray]

AND, something I left out is that I also use a "split" AC for some armor types. Heavy mail has an armor bonus of +5/+3, with the higher bonus applying to slashing and piercing, and the lower bonus applying to all other damage types. "Normal" mail is +4/+2, and light mail is +3/+1. This may be getting too complex for its own good, but to me it makes sense that certain armor was more effective against certain damage types. Why have damage types otherwise?

 

[Sadras]

Valiant effort.

I have done something similar but a little simpler.
MELEE AC = 8 + proficiency bonus + dexterity + shield bonus
RANGE AC = 8 + proficiency bonus + dexterity + 2 x (shield bonus)

If you are unarmed the proficiency bonus is 0, if you are not proficient with the weapon you are using the proficiency bonus is halved (rounded down).

And then introduced damage prevention on the actual armour worn.
Shield bonus also assists with area type saves (but not against cloud/gas attacks).
Fighting Defensively doubles your proficiency bonus (minimum of +2 if you are unarmed)

I've had to add some weapon properties (disarm, fast, impale, hew, hook, parry, piercing, powerful, shattering, slow, staggering, unwieldy...etc) and adjusted some feats & spells naturally.
So a weapon with a parry bonus increases your AC in melee.

Weapon bonus is 0 (short - dagger, short club), 1 (most one-handed weapons), 2 (most two-handed weapons), 3 (reach weapons like polearms and long spears)
- Barbarians use their Constitution modifier instead of Armor bonus if it is higher.

To be fair simple spear weapons and chain/ball weapons are not great for parrying.
Ball and chain are better for disarming.

 

[Joel Spanky Gray]

To be fair simple spear weapons and chain/ball weapons are not great for parrying.
Ball and chain are better for disarming.

I like that you doubled the shield bonus for Ranged AC, and I like the additional weapon properties. I also like the Fighting Defensively aspect. The system needs them! I have found that armor as damage reduction doesn't work well in any version of D&D - it interacts poorly with most spells and requires the introduction of a lot of supplemental rules to handle chinks in armor, armor coverage, hit locations, etc.

However, from my experience spears and pole weapons are EXCELLENT for parrying and keeping enemies at bay. They are extremely nimble, long, and durable. I would agree with you about the ball and chain, but a defense bonus for a weapon is not just its parrying potential, but its threatening range and ability to keep enemies at a distance. I abstract parrying and reach as a generic weapon bonus to AC. For more detail, you could use a system like GURPS or RUNEQUEST, where parrying is a separate ability.

 

[Sadras]

I have found that armor as damage reduction doesn't work well in any version of D&D - it interacts poorly with most spells and requires the introduction of a lot of supplemental rules to handle chinks in armor, armor coverage, hit locations, etc.

I agree with you on this. We are testing out my house ruled 5e this December. We definitely won't have called shots (hit locations), armour coverage and chinks in armour.
I would add and an additional die or two to most damage dealing spells to overcome the armour prevention.
Sleep bypasses armour and magic missile doesn't care for it, so they remain the same. I would generally apply some common sense. For instance Barkskin improves prevention, while Shield still improves AC as does Mage Armour since its force-based.

However, from my experience spears and pole weapons are EXCELLENT for parrying and keeping enemies at bay. They are extremely nimble, long, and durable. I would agree with you about the ball and chain, but a defense bonus for a weapon is not just its parrying potential, but its threatening range and ability to keep enemies at a distance.

Bolded emphasis mine, good point - 100% agree.
The problem with the spear and polearm is they are pretty lousy in a knife/dagger fight. I guess it all depends on the level of detail one is prepared to deal with. 5e likes to keep it simple - I try as best to stick to that, sometimes I fail miserably.

 

[Dausuul]

My standard house rule question: What, specifically, are you trying to achieve here?

It looks like the goal is to tweak the AC rules so that:

• Everyone has an incentive to invest in Dex, even heavy armor wearers.
• Having a long weapon improves your melee defense.
• Defense naturally improves with level.
• Don't mess up the current game balance too much.

These all seem like reasonable goals, but holy cow, this is a Rube Goldberg way of achieving them. Here's a simpler approach, subject to fine-tuning via playtesting:

When you're hit by a melee attack, if you're wielding a melee weapon, you can use your reaction to deflect it. Make a DC 12 Dexterity check with proficiency. If you succeed, add +1 to your AC against that attack if your weapon is light; +2 if it's neither light nor heavy; or +3 if it's heavy.

You can't use this ability again until you take an action to reset your stance, or until you score a critical hit in melee.

My reasoning: Assuming you aren't going to waste a whole combat round recharging, you'll get to use this once per combat, maybe twice if you use it and then happen to crit. Because you use it after seeing the attack roll, you'll always use it when it can change a hit to a miss; thus, having a bigger weapon doesn't mean you deflect more attacks, but it does give you more control over when to use it. A light weapon wielder pretty much has to deflect any time they get the chance, where a heavy weapon wielder can afford to say "No, I'll eat the hit from the kobold and hold my deflect for the ogre."

I chose DC 12 because the highest bonus you can have on the Dex check is 11; thus you always benefit from investing in Dex and gaining levels, but the check is easy enough that it does not massively favor the Dex fighter over the Str fighter.

 

[Ovinomancer]

I like that you doubled the shield bonus for Ranged AC, and I like the additional weapon properties. I also like the Fighting Defensively aspect. The system needs them! I have found that armor as damage reduction doesn't work well in any version of D&D - it interacts poorly with most spells and requires the introduction of a lot of supplemental rules to handle chinks in armor, armor coverage, hit locations, etc.

However, from my experience spears and pole weapons are EXCELLENT for parrying and keeping enemies at bay. They are extremely nimble, long, and durable. I would agree with you about the ball and chain, but a defense bonus for a weapon is not just its parrying potential, but its threatening range and ability to keep enemies at a distance. I abstract parrying and reach as a generic weapon bonus to AC. For more detail, you could use a system like GURPS or RUNEQUEST, where parrying is a separate ability.

Um, your experience isn't matched by history, where polearms were used in formations and not by skirmishers. If your opponent is in front of you, and lacks a shield, yes, you have great ability to keep them at bay with the pointy bits. If they have a shield or heavy armor, though, the telegraphing nature of the strikes a polearm makes means they can interpose the shield or a sufficiently armored body part while they close inside your reach. The time to recover and shorten your grip to fight somewhat effectively within your reach is the time they stick their pointy ends into you. If you fight more than one opponent, the time to turn your weapon leaves you vulnerable. This is why polearms were used in formations where the pointy bits made for a hard to breach line rather than by skirmishers where the length and clumsiness (and arguing a halberd isn't clumsier than an arming sword or axe is silly) made for dead skirmishers.