Armor as DR in DnD5 – corrections must be made

In my pondering of heretical D&D concepts from the other day, one of the thoughts that I had was:

Wow, rolling vs. a “Defense Target” of 10+DEX Modifier is going to make even very experienced fighters get hit an awful lot. On the other hand, armor subtracts from damage. How does that balance out?

Guess it’s time to break out Excel. First thing that leaped out at me was that the armor was wonky.

The Armor Progressions Don’t Line Up

I’m not going to show my work here, but the armor progressions for DR don’t work as I wrote them. The short version is that the AC progression sets the value of armor a certain way, and that means that each successive armor that gets a bonus should have some level of improved protection over the next one.

The progression I have, while elegant, creates artifacts that don’t increment well with the AC table.

Consider the table again. 1d4+1 is supposed to be AC 5 based on the maximum roll. That’s all well and good, but when I simulated the dice rolls 250,000 times, it was clear that I made the wrong call here. You need to treat average damage resistance, not the maximum. 1d4+1 averages 3.5 Damage Resistance. So does 1d6. But 1d6 is supposed to be the better armor. So phooey, that doesn’t work.

Now, if I instead treat the current AC bonus as, say, a half-point less damage than what the dice should roll, that gives padded armor an expected resistance of 1.5 points . . . or 1d4-1. Plate, with an expected resistance of a whopping 8.5 points, might be 1d12+2. Let’s keep only 1d rolling no matter the die size, and look at options for appropriate averages that work with the Armor Class scale.

In order to get to plate, we need 1d12+2. That’s a lot of damage. It means a great axe or greatsword wielded by a strong person will still wind up getting “bounced” frequently. Plus (and again, not showing my work), some of the armor values mean that you’re going to need to hit several to dozens of times more frequently in order to get the same HP of damage through. That will make fights last a really, really long time.

So even before we start, let’s give padded (AC 11, or bonus of +1) an expected protection of 0.5 instead of 1.5. If we disallow any bonus more than +1 or penalty more than -2 (and prefer -1 to +1), we get the possibilities for armor dice to the right.

That shows we have a lot of choices, which is nice. I’ve color-coded the light/medium/heavy proficiencies to see if there’s something logical we can eke out of it. Turns out there is.

We can restrict the light armors to rolling d4, and the medums to d6. Heavy armor gets d8 through d12, with d12 reserved for the suit of plate armor, because it’s more awesome that way. Choosing it that way, and re-ordering the table by proficiency then AC (like it is in the PHB) we get a fairly satisfying table:

The only potential problem children are the -2s for Padded, Leather, and Hide, which for the first two means you have a 50% chance that your armor provides no protection whatsoever, while Hide is a 33% chance. That actually helps Hide armor, because on the straight-stat level, Hide kinda sucks. Sure, it’s only 10gp instead of the 45 for studded leather, but it’s basically the same weight, AC, and Hide hits you with a maximum bonus of +2 to DEX.

Parting Shot

This table is more consistent with the Armor Class values given in the PHB, so you won’t get strange results like I did when I calculated armor values based on the maximum protection and allowed 2d4 as the base roll. That had cases where the superior armor in-game was no longer better protection, and while I suppose that could be considered a design feature, keeping the same relative protection values for the armors listed seemed like it would be worth doing. Alternately, there’s no good reason to change it, and it’s easy to preserver.

I like how it wound up. Light armors are d4, medium are d6, and heavy armor is “higher than d6,” with the very inexpensive ring mail (less expensive than studded leather!) having a chance of zero protection. Better buy smaller rings.

9 thoughts on “Armor as DR in DnD5 – corrections must be made

  1. I'd consider building heavy armor on 2d – instead of getting really high protection (but letting low damage through relatively often) they would offer reliability. 2d4-1, 2d4, 2d6-1, 2d6.
    Remember that in practice, there are basically 2-3 popular armor types in any edition' they migh as well have straightforward dice.

    Also, you have "Spint" as an armor type.

    1. Yeah, typo.

      Ring mail is kinda crap armor, so I don't have a problem with that one being where it is based on 1d. The other heavy armors might be based on 2d4 (average 5), so chain mail would be 2d4, splint would be 2d4+1, and again, because it's so much more expensive and rare, full plate armor might be a flat 2d6 or even 2d6+1 (so it's better in every way than splint).

      The danger here will come in a level of invulnerability . . . but I think I have a couple of thoughts on that too.

      Thanks for the comments!

  2. Very interested in both these articles and the one regarding using armor type to determine criticals. Between this article and the previous on armors, where do you put the bonuses from magical armor…Defense Threshold increase? Shielding Threshold? Wound Threshold Increase? Armor Damage Absorption Boost? Or a Blend of all/some of these?

    1. I think it might be a bit ad hoc. A Cloak of Protection should make you generically harder to hit, so I'd put that one as a Defense Threshold boost, I think.

      A magical bonus to armor right now simply makes you harder to hit, boom, full stop. So increasing defense threshold would make some sense. It's also going to wind up being a lower percentage improvement than +1 to some sort of armor bonus, as the damage reduction is a bigger deal.

  3. Also, when considering all 3 articles, where does this put classes like Barbarian and Monk who were getting built-in perks for wearing no armor? Do they get thrown some other kind of bone or does it still balance out OK?

    I also thought about how adding small (+1 standard 5th ed AC, no dex mod bonus cap), medium (+2 standard 5th ed AC, +4 dex mod bonus cap), large (+3 standard 5th ed AC, +2 dex mod bonus cap), and tower shield (+4 standard 5th ed AC, no dex mod bonus) options.

    1. One step at a time. 🙂

      I think for Monk, clearly, the key will be increased Defense threshold (because he's just harder to hit) and perversely, higher Stress Points (representing martial prowess). Barbarians probably just get more Stress Points.

      The other way to go would be to give one or both a few points of some sort of natural DR. Call it tough skin.

  4. An issue with dice adds is how they interact with small attacks. Consider a critter that hits for 4 points of damage. Expected damage, by armor type:
    Padded/Leather: 3.25
    Studded Leather: 2.5
    Hide: 2.33
    Chain Shirt: 1.67
    Scale, Breastplate: 1.0
    Half Plate: 0.5
    Ring: 1.25
    Chain Mail: 0.6
    Splint: 0.3
    Plate: 0.25

    Notably, half plate (raw AC 15) is better than chain mail (raw AC 16).

    1. I'm sure there will be plenty of artifacts. At some point – and that point is pretty early in this process – I will simply shrug and say "Yep, that's different than it used to be."

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