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Imagine a Party with 4 characters. Each one has different AC:

  • 14 AC/48 HP (squishy caster)
  • 15 AC/50 HP
  • 16 AC/50 HP
  • 17 AC/54 HP (the tank)

The Party picks up a Ring of Protection +1. Who "should" get it for Party survivability?

  • The squishy caster to even things out?
  • The tank to make them tankier?
  • One of the others, to make them generally tankier/hardier?

I know that it ultimately becomes situational (Does the squishy caster run into danger all the time? Does the tank get distracted with picking flowers on the side of the battlefield?), but assuming a "typical" marching order and battle roles, who should get it?

I'm torn between making the tank tankier or bolstering the caster.

Is there general wisdom or is there a model that applies? Does it purely come down to: 'who will be the target of weapon attacks more often?'

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    \$\begingroup\$ Do you have any additional information about your campaign you can share? The answer might be different if you are fighting primarily ranged vs melee enemies, or if you are in tight corridors or open fields. I do suspect that your lattermost statement is what will be right, but I think there is a possibility of a mathematical analysis assuming everyone gets attacked the same amount. \$\endgroup\$
    – ESCE
    Jul 27 at 18:43
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    \$\begingroup\$ I play d20 games since D&D 3.0 came out and I have never seen typical marching order. Even the same person playing the same type (caster, melee, etc) could have radically different approaches and results. \$\endgroup\$
    – Mołot
    Jul 28 at 6:51
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    \$\begingroup\$ Do you have a healer in the group? If you've only got one its pretty important you minimise the chances that they go down. \$\endgroup\$ Jul 28 at 8:14
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    \$\begingroup\$ Why would you specifically get to assign the item in question? \$\endgroup\$
    – Weckar E.
    Jul 28 at 8:33
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    \$\begingroup\$ @schroeder When you don't need to keep the healer conscious to survive encounters. \$\endgroup\$
    – TylerH
    Jul 28 at 14:22
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Generally-speaking, AC is stronger the more AC you have.

For instance, an enemy that has to roll a 19 to hit has a 1/10 chance to hit, and would have a 1/20 chance if they needed a 20. A single +1 AC can effectively double your defense (assuming it's high enough).

You'll probably get more value adding AC to those that anticipate being attacked, while your other members should get the non-AC benefits (THP, save bonuses, etc).

Of course, if your DM is the kind to ignore the 20 AC Fighter, it's probably better to spread out those items or have the Fighter pick up things that make him a better target (like the Sentinel feat or the Cavalier subclass).

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    \$\begingroup\$ I show the wild difference +2 AC makes in survivability in my answer here: How do I explain to an AD&D player that items that increase Armor Class in D&D 5e are overpowered? \$\endgroup\$ Jul 27 at 19:20
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    \$\begingroup\$ Ring of Protection provides more than just AC - it may be helpful to address the save value in the calculus for picking who should get it. \$\endgroup\$
    – NautArch
    Jul 27 at 21:09
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    \$\begingroup\$ Good point about gaming your DM -- some DMs run "smarter" enemies whose tactics might involve targeting weaker members of the party, taking out the healer, etc. Other DMs just drop a bunch of guys on the map and let them run straight at the closest character. \$\endgroup\$
    – A C
    Jul 29 at 2:39
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    \$\begingroup\$ Not sure I buy this logic. A +1 to your AC may indeed halve the chance of taking a hit if your initial AC is high enough, but in terms of "how many attacks do I expect it to take to down me?", going from 15 to 30 is meaningless. It's a tiny change in actual survivability (i.e. you were going to survive a vast number of AC attacks anyway). Meanwhile a character whose AC is a modest 13 or so will get a better real effect from a +1 because their expected survival goes from like 4 attacks to 5, which is enough to stay up in a battle where they would otherwise fall. \$\endgroup\$ Jul 29 at 14:33
  • \$\begingroup\$ @DarthPseudonym Fair point, but it's worth mentioning that a Wizard has about half the HP of a Fighter. Essentially, as long as they're getting attacked half as many times as the Fighter or less, you're still getting more value adding the AC to the Fighter. Spot defenses, like Mirror Image or Shield, are probably a better strategy for a caster to leverage rather than a +1 AC that's only going to be relevant against 1 attack per combat anyway. \$\endgroup\$ Jul 29 at 16:30
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This can probably only be determined empirically

Because of the wide variation in play styles among both players and DMs, I don't think it's possible to give a general recommendation. The best approach I can think of is the empirical approach: pick a reasonable objective to optimize, and dole out the defense buff based on who has historically been most lacking in that area. The objective should be related in some way to survivability, such as:

  • which character gets hit the most (total number of hits, not fraction)
  • which character takes the most damage
  • which character gets knocked unconscious the most often

Additionally, the objective should be something the ring can influence. In this case you should consider hits/damage/KOs from both attacks and failed saving throws, since the Ring of Protection affects both AC and saving throw modifiers.)

Let's say you choose the first one. Now ask: among the party, who takes the most hits in practice? If the tank with 17 AC is doing a good job of soaking up attacks, maybe it's them. If the tank is not doing a good job, or if the party has been frequently put in situations where the tank is unable to do so (e.g. swarms of enemies or big AOE spells), then maybe the squishy caster is taking too many hits due to their low AC. Maybe the 2 characters with the highest AC (16 and 17) have both ended up tanking equally, but the 16 AC character is getting hit more due to their lower AC, and they need the buff most. You don't actually need to count up every hit in every past fight; you probably have at least a vague sense of the answer without having to do so.

In summary:

  1. Choose the empirical statistic you most wish to optimize.
  2. Decide who is doing the worst in this statistic, and give the item to them, since they need it most.

I believe this will have the greatest impact because ideally, you want to spread out incoming damage exactly in proportion to each character's hit point maximum (i.e. the opposite principle from focusing one enemy down at a time). In the most ideal case, if damage is spread out so that every character takes 99.9% of their hit point maximum (rounded down) in damage, they will all still be standing while having taken the maximum amount of damage possible. Shoring up the defenses of whoever is taking too much damage gets the party closer to this ideal case.

Lastly, I'll note that this all assumes that future combats will be similar to past combats, since you are using past combat performance to make a decision that will affect future combats. If you have reason to believe that future combats will be substantially different, then you will need to adjust accordingly.

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Below is a table that lays out how increases in armor class affect relative survivability of a character. For each Armor Class, we assume the character has 100 hit points, and we calculate (on average) how many rounds it takes for a level 1 character with 16 strength, wielding a greatsword, to knock them down to 0 hit points. We will then use this to compare (again, on average), how much a 1 point increase in Armor Class improves their survivability.

Base AC +1AC from Magic Item % Difference "Effective HP" "EHP" w/+1AC
AC5 10.771 10.771 0.000% 100 100
AC6 10.771 10.771 0.000% 100 100
AC7 10.771 11.349 +5.366% 100 105
AC8 11.349 11.992 +5.362% 105 111
AC9 11.992 12.713 +5.671% 111 118
AC10 12.713 13.526 +6.011% 118 126
AC11 13.526 14.449 +6.388% 126 134
AC12 14.449 15.508 +6.829% 134 144
AC13 15.508 16.735 +7.332% 144 155
AC14 16.735 18.172 +7.908% 155 169
AC15 18.172 19.879 +8.587% 169 185
AC16 19.879 21.941 +9.398% 185 204
AC17 21.941 24.479 +10.368% 204 227
AC18 24.479 27.682 +11.571% 227 257
AC19 27.682 31.848 +13.081% 257 296
AC20 31.848 37.491 +15.052% 296 348
AC21 37.491 45.564 +17.718% 348 423
AC22 45.564 58.066 +21.531% 423 539
AC23 58.066 80.019 +27.435% 539 743
AC24 80.019 128.569 +37.762% 743 1194
AC25 128.569 128.569 0.000% 1194 1194

Obviously, at unrealistically low armor classes, the +1 does nothing; the greatsword-wielding character cannot roll lower than a 6 on their attack roll, so they'll hit 95% of the time against any character with an armor class of 7 or lower. Conversely, as the armor class goes up, each point of armor class represents a greater and greater relative survivability, not just compared to the lowest armor classes, but relative to the next highest armor class.

This tells us that, in general, each point of Armor Class becomes more valuable proportional to how much a character already has. A paladin with 20 armor class gains a much larger survivability boost from going to 21 armor class than a wizard at 15 armor class gains from going to 16.

This also doesn't take into account the raw hit point differences between a highly armored paladin and a lesser-armored wizard, although we could apply the "% Difference" column from the table to work that out.

So it's transparently obvious from the example at your table that the "tank", with 54 hit points and 17 armor class would receive the most substantial boost in survivability by going to 18 armor class.

Of course, that isn't to necessarily say that they are the one who should receive the ring. If the weakest character is frequently vulnerable to attacks, then that +1AC might be the difference between them going down or staying up at a critical moment, in a way that the "tank" is already not particularly vulnerable. That is a judgement that your party will have to make for themselves.

But if the goal is raw survivability of the party, then any item that boosts armor class should always be given to the party member who already has the highest armor class, up until the point where their armor class exceeds what their enemies can roll on a natural 20.

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  • \$\begingroup\$ You can probably take ACs 1-4 off the table, I’m pretty sure the lowest possible AC for a PC is 5 (10-DEX) when your Dexterity modifier is -5. If you want to stick with realistic ACs, cut it off at 10. \$\endgroup\$ Jul 28 at 6:10
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    \$\begingroup\$ @ThomasMarkov I was thinking in terms of including monster ACs, which do occasionally dip below 10 (even for decently-leveled creatures!) but I do agree that 5 is probably a good cutoff. \$\endgroup\$
    – Xirema
    Jul 28 at 6:20
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There will never be a "one size fits all" rule

That being said consider extra survivability options different classes, feats and spells may give beyond the standard HP and AC survivability of the group. Some general things to consider:

  • Barbarian's Rage: This provides resistance to damage from mundane attacks (piercing, slashing and bludgeoning) - this means a boost to AC isn't blocking as much damage on this character as it may on a different one with equal AC
  • Druid's wild shape: Wildshape gives a great pool of HP and, whilst using it, this class won't benefit from the extra AC so the ring would be better on a different character to improve survivability of the group
  • Healers: You want to increase the chance these survive to bring back the rest of your party - this would be my safest bet for the increase to AC. From experience if you've got a cleric who is worried about stepping into the fray to cast their cure wounds or is the first to fall then the survivability of your party drops drastically.
  • Sentinel: This feat is amazing for that front line fighter. If you have a party member with this feat I'd give them the ring even over the healer - if no one can get through to your healer then you don't need to worry so much about them taking damage.
  • Spells: Anything that ensures your tank is center of attention for the BBEG (i.e. Compelled Duel) is a tactic that requires the tank to have the highest AC possible.

At the end of the day, however, a ring is great for situations like this. You don't need to know before going in who is most in need because the ring can change hands on long rests. Just play with your party, see what sorts of encounters are coming your way, and switch the ring around when needed.

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  • \$\begingroup\$ So, from a modeling perspective, 1. AC is not the only attack defense (e.g. resistance, and THP/wild shape), and 2. Damage attractors (e.g. Sentinel, Compelled Duel) would require greater defense since the Party member is acting as a shield for the other members. \$\endgroup\$
    – schroeder
    Jul 28 at 10:59
  • \$\begingroup\$ I know what you are trying to say about the concern for the Healer, but I think that's a 2nd order concern in relation to the general factors. The concern could be mitigated by a variety of factors, and AC might not be an effective mitigation for that concern. \$\endgroup\$
    – schroeder
    Jul 28 at 11:01
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    \$\begingroup\$ @schroeder Yeah, the answers which just show a pure statistical approach to AC aren't covering all the bases - you've got to consider there are other ways damage can be avoided/mitigated. The healer being secondary really depends on the encounters and the difficulty. If your front line fighter will take the brunt of attacks then great but if the enemies focus on your healer to bring them down I'd much rather that fighter drop than, potentially, the only one who can revive the rest of the party. Prioritisation will depend on the situation really. \$\endgroup\$ Jul 28 at 12:38
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My inclination would generally be to:

a) if the party mostly adventures in confined spaces where one person can defend the others, it best goes to the existing tank, or

b) if the party adventures in more open areas, and/or fights enemies that are more mobile, it best goes to the third character, the 16 AC/50 HP guy, to create a second good tank to help hold the line.

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    \$\begingroup\$ Please review our expectations for supporting answers. This answer does nothing to explain why you would do these things. Why are these suggestions good ideas? How do you know that these things aren't worse than alternatives? \$\endgroup\$ Jul 27 at 20:45
  • \$\begingroup\$ The reasons are stated in the answer already. In case (a) it is so the one person can defend the others better. In case (b) it is so the two defenders can hold the line better. \$\endgroup\$
    – PhilB
    Jul 27 at 20:48
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    \$\begingroup\$ Those are just the solutions, not why those solutions are good. \$\endgroup\$ Jul 27 at 20:51
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    \$\begingroup\$ @PhilB Your previous comment has now been removed twice for violating the Code of Conduct. You need to support your answer with more than just a statement, why are your suggests the best option? See What are the Citation Expectations on RPG Stack Exchange? for more information. \$\endgroup\$
    – linksassin
    Jul 28 at 5:44
  • \$\begingroup\$ I need to explain why a better defense is good? That's ridiculous. It isn't a rules question, so rules and citations aren't relevant. It's an allocation question about a defensive item, so they already get that defense is good, and are asking where to use it. I answered that question directly. If you think it needs a better answer, then you can write one yourself. \$\endgroup\$
    – PhilB
    Jul 28 at 14:44

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