Adamantine Armor 5e: Critical Hit Immunity, Cost and When It Beats +1 Armor

Adamantine Armor in 5e is uncommon magic armor that turns every critical hit against you into a normal hit. It can be any medium or heavy armor except hide, and it doesn't require attunement. That's the whole item: no AC bonus, no resistance. Against ordinary attacks the effect is small, a 5 percent chance per attack of avoiding some extra dice. Against the things that cause automatic critical hits (Paralyzed and Unconscious targets, a 2014 Assassin's surprise round), it cancels every one of them, and while you're dying each hit costs you one death saving throw failure instead of two.

Table of Contents

• •Adamantine Armor Rules Text
• •How Adamantine Armor Works
• •Adamantine Armor: 2014 vs 2024
• •Is Adamantine Armor Worth It?
• •Adamantine Armor for DMs
• •Frequently Asked Questions

Adamantine Armor Rules Text

The two printings say the same thing. The 2024 text capitalizes Critical Hit as a defined game term and spells out the armor list ("Any Medium or Heavy, Except Hide Armor").

How Adamantine Armor Works

What a critical hit normally does

In both editions, a critical hit happens when the d20 for an attack roll shows a 20. The attack hits regardless of the target's AC, and the attacker rolls all of the attack's damage dice twice. Any other dice riding on the attack, such as a Rogue's Sneak Attack, are doubled too. Modifiers are added once.

Adamantine Armor removes the second half. The natural 20 still hits you, even if your AC would otherwise make the attack miss. It just deals normal damage. The armor doesn't turn crits into misses.

Automatic critical hits: the real reason to wear it

Two conditions turn every hit from within 5 feet into a critical hit: Paralyzed and Unconscious. Both also give attackers Advantage. This is where adamantine stops being a 5 percent effect and becomes a 100 percent one.

• •Hold Person and Hold Monster. A failed Wisdom save leaves you Paralyzed. Every melee hit is a crit. With adamantine, none are.
• •Ghoul claws. A failed DC 10 Constitution save paralyzes you. In 2014 that lasts up to 1 minute (you repeat the save at the end of each of your turns), and the 2d6 + 2 bite averages 16 as a crit instead of 9. In 2024 it lasts until the end of your next turn, still long enough for the rest of the pack to land automatic crits; the 2024 bite (1d6 + 2 plus 1d6 Necrotic) goes from 8.5 to 16.
• •Dropping to 0 Hit Points. You're Unconscious, so any melee attack that hits you is a crit.

Death saving throws

Taking damage while at 0 Hit Points costs you one death saving throw failure, and damage from a critical hit costs two. Three failures and you die. An enemy who keeps swinging at a downed character within 5 feet lands crits, so two hits kill. In Adamantine Armor, each hit is a normal hit and costs one failure, so it takes three. That one extra hit is often the round your healer needed. See death saving throws for the full rules.

Bigger dice, bigger savings

The armor saves you the extra dice, so it matters more the more dice an attack carries.

The 2014 Assassin also has Assassinate: any hit it scores against a surprised creature is a critical hit. In adamantine, an ambush by a 2014 assassin deals about half the damage. The poison saving throw (7d6 on a failed DC 15 Constitution save in 2014) isn't part of the attack's dice, so a crit never doubled it.

Spell attacks count too. The text says "any critical hit against you", so a Fire Bolt that rolls a 20 deals its normal dice.

What adamantine doesn't stop

Some effects trigger on the d20 roll itself rather than on the critical hit. The Vorpal Sword cuts off a head when the wielder "roll[s] a 20" on the attack roll, and the Sword of Sharpness adds damage the same way. Neither text mentions critical hits. The armor turns the crit into a normal hit, but the 20 was still rolled, so the beheading or bonus damage still happens.

Abilities that widen the critical range work as written, then get cancelled. A Champion Fighter's Improved Critical lets them crit on a 19 or 20; against you, those are still normal hits.

The 2014 monster entries that resist or ignore "nonmagical attacks that aren't adamantine" (golems and gargoyles, among others) refer to adamantine weapons. Your armor has no bearing on them.

Armor types and cost

The 2024 SRD prices magic armor as the item's rarity value plus the base armor. Uncommon is 400 GP, so:

Hide armor is excluded. The armor keeps all its normal properties: AC, Strength requirement and Stealth Disadvantage. Adamantine Plate still needs Strength 15 and still makes you clank.

Adamantine Armor: 2014 vs 2024

Nothing about the item changed. The rules around it barely moved either. Both editions double the damage dice on a crit, and both make hits against Paralyzed or Unconscious creatures within 5 feet into crits. Two 2024 monster changes shift its value. The 2024 Assassin lost Assassinate, so it only crits on a 20, but its shortsword carries 5d6 poison dice that a crit would double. The 2024 Ghoul paralyzes for a single turn instead of a minute.

Is Adamantine Armor Worth It?

It depends on what's attacking you. The armor competes with +1 Armor for your one armor slot, and neither needs attunement.

Against ordinary attacks, +1 Armor wins. An ogre (+6 to hit) attacking AC 18 hits on a 12 or higher, 45 percent of the time; against AC 19 it hits on 13 or higher, 40 percent. That 5 percent fewer hits saves 0.65 damage per attack (5% × 13). Adamantine saves 0.45 per attack (the 5 percent chance of a 20 × the 9 extra crit damage). +1 Armor is also rare, so it's worth ten times as much under the 2024 value table.

The comparison flips when crits stop being random:

• •Front-liners who drop to 0 Hit Points. Turning a two-hit death into a three-hit death is worth more than 1 AC to a barbarian or fighter who goes down a lot.
• •Campaigns with paralysis or ambushers. Ghouls, ghasts, Hold Person casters and 2014 Assassins all lean on crits.
• •Characters with low Wisdom saves. A fighter who fails against Hold Person is the target this armor was made for.

Who doesn't need it: anyone in light armor (adamantine only comes in medium and heavy), and back-liners who rarely get hit in melee. Wizards and rogues are better off with a Cloak of Protection.

Compare the other SRD armor upgrades that skip attunement:

Only one can be your armor. If a front-liner gets to pick between adamantine and mithral plate, the question is whether they die more often to crits or to the Strength 15 requirement and failed Stealth checks.

Adamantine Armor for DMs

Where it turns up. Uncommon, no attunement and a modest price (450 GP for a chain shirt), so it works as early loot or a blacksmith's special order. Dwarven forges and old fortress armories make obvious homes for it.

What it changes. Very little most of the time. It quietly blunts the scariest moments in low-level play: the critical hit that drops a fighter from full, the ghoul pack around a paralyzed paladin. If your encounter relies on Hold Person plus melee attackers, it fails against the character in adamantine.

At the table. Remind yourself when the player is wearing it. The easiest mistake is rolling crit damage out of habit. A natural 20 still hits; just roll the dice once.

Pricing. 400 GP plus the base armor under the 2024 SRD (table above). The 2014 SRD has no price for it. The shop price calculator helps if you're stocking a smithy, and the magic item generator can roll something else for the hoard.

Hooks.

• •A mine has struck a vein of adamantine, and the smith who can forge it wants the party to clear the lower tunnels before she'll make them anything.
• •The party finds a suit of adamantine half plate on a skeleton in a ghoul warren. The ghouls left it alone, which should tell them something.
• •An Assassins' guild pays a bounty for any adamantine armor in the city, to keep it off their targets.

Whose armor is adamantine, and who's still waiting for the smith's order, gets lost between sessions. Loreify records the game and writes the recap, loot included.

Frequently Asked Questions

What does Adamantine Armor do in 5e?

While you wear it, any critical hit against you becomes a normal hit, so the attacker doesn't roll extra damage dice. It's uncommon, comes as any medium or heavy armor except hide, and works the same in the 2014 and 2024 rules.

Does Adamantine Armor require attunement?

No. Neither the 2014 nor the 2024 SRD requires attunement, so it doesn't use one of your three attunement slots.

Does Adamantine Armor protect against attacks on paralyzed or unconscious creatures?

Yes. Hits against a Paralyzed or Unconscious creature from within 5 feet are automatically critical hits, and the armor turns each of them into a normal hit. At 0 Hit Points that means one death saving throw failure per hit instead of two.

Does Adamantine Armor give AC or resistance?

No. It has the base armor's normal AC and no damage resistance. Its only effect is cancelling critical hits.

How much does Adamantine Armor cost?

Under the 2024 SRD it's 400 GP (the uncommon value) plus the base armor's cost: 450 GP as a chain shirt, 1,900 GP as plate. The 2014 SRD doesn't price magic items.

Does Adamantine Armor stop a Vorpal Sword?

No. The Vorpal Sword's beheading triggers when the attacker rolls a 20, not on a critical hit, so the armor cancels the extra damage dice but not the beheading.

Item text: System Reference Document 5.1 (2014) and 5.2.1 (2024), Wizards of the Coast, CC-BY-4.0. Analysis, rulings and ideas are Loreify's own.