Which magic weapon deals the most damage?

Question

Which magic weapon deals most damage at each rarity tier? (I am not asking about Artifacts, just normal rarity scale magic items).

For the sake of defining weapon damage:

• Direct expected damage from a hit (not maximum possible damage)
• Damage upon hit, not damage over several rounds (although mentioning weapons that can deal ongoing damage as bonus info is fine)
• Raw damage, unaccounted for resistances, saves and vulnerabilities (expected damage accounting for them for the “average” monster would be a useful bonus as saves and resistance against something like poison can have a big impact)
• Damage from magic weapons that you attack with only, not things like wand of fireball
• Sustainable damage that is applied with every hit, not abilities that can only be used a limited number of times, or limited number of times per day
• Include improved hit rate contribution from pluses to attack assuming the combatant has a +5 ability bonus adding to the resulting damage but no other special effects (like hex, hunter’s mark, etc.); assume that advantage granted by the weapon adds +4 to hit chance, or 20% added damage from converting a miss into a hit
• Assume a critical chance of 5.26%¹ (no special classes, feats, advantage or disadvantage), if it is relevant for damage calculations
• Moonblade hacks with multiple prior owners are outside the scope.

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¹ To make damage calculations comparable, use the expected base damage assuming a hit (without hit chance adjustment for different ACs), and add additional damage from critical hits. As we assume a hit already, and a 1 would always miss, there are only 19/20 possible d20 results to account for for a critical, so use 5.26% chance for that.

You can in addition provide the expected damage against an average AC that gives you a base 65% hit chance (and if you like use increased hit chance on that base from advantage), and use the normal 5% critical chance for that.

Answer 1

Common Weapons

There are only 4 common magical weapons over all the books. Only 2 of those are actual weapons, the others are ammunition.

• Moon-Touched Sword
• Armblade

Since the Moon-Touched Sword can be any sword, we will assume it is a greatsword and therefore dealing 2d6(7) damage on a hit. If we add the 5% chance of getting a critical hit to it, we get an average damage of 7 + 5.25% * 7= 7.3675. (7 average from base hit, and 5.25% chance to add another 7 from a crit).

Average damage for a Moon-Touched Greatsword: 7.4 slashing damage

Uncommon Weapons

There are a total of 18 uncommon weapons listed, with almost all of them being +1 weapons of some kind, or having charges, which disqualifies their use here.

Some deal extra damage against undead or against one very specific creature, but since we don't want to have any special cases in here the best choice is a +1 greatsword, dealing 7 + 5.26% * 7 + 1 + 1/20*(7+1+5) from 5% increased to hit chance, for a total of 9.0182 slashing damage.

Average damage for a +1 greatsword: 9 slashing damage

Rare Weapons

The flame tongue greatsword deals 2d6 slashing plus 2d6 fire damage when lit, which also doubles on criticals, for 14 + 5.26% * 14 = 14.7364.

Average Damage for a flame tongue greatsword: 14.7 (half slashing, half fire damage).

Very Rare Weapons

The oathbow longbow is a corner case - the number of attacks that can be enhanced is not limited, but it only works against one creature per day. It deals 1d8 piercing + 3d8 piercing granting you advantage on the roll. In this case, we will assume advantage (as it is part of the weapons effect). We'll treat the average benefit of that as a +4 (20%) on the to hit chance, and doubling the chance for a crit. Total (4.5 + 3 * 4.5) + 2 * 5.26% * (4.5 + 3 * 4.5) + 20% * (4.5 + 3 * 4.5 + 5) = 24.4936.

Average damage for Oathbow Longbow: 24.5 piercing.

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The data in this answer is in part based on what you can find by searching the magic item list on D&D Beyond for items of type "weapon" here.

Answer 2

Wave can do some out of whack nova damage

There is a legendary item (not artifact) in the DMG called Wave which has the property of doing half of a creature's HP in damage on a critical hit. If you put it in the hands of, for example, a Champion Fighter at level 15, they do a critical hit on an 18, 19, or 20. Apply that to three attacks per round (with a burst of six attacks on a round where Action Surge is activated) and fight against a monster with 200 HP (an efreet for example) and you can get some way out of scale damage spikes. (100 piercing damage with, due to it being a magical weapon attack, gets no damage reduction). Do it against a creature with 400 HP and you see a 200 HP spike.

A level 20 Fighter/Champion who gets four attacks per round with that larger crit chance will now and again get similar spikes.

There are a variety of crit fishing builds one can try this with, adding things like Haste and a variety of ways to offer advantage on all attacks (buff the Fighter with Foresight, for example, so that for 8 hours all attacks are with advantage) that boosts the Critical hit chance even further.

Yes, Wave is an edge case, and this damage boost scales with the total HP of the target, but when it activates the HP on a hit is massive, even though its nominal damage out put is 1d8 + (STR mod) +3 when used 2-handed.

And, it can be found in a level 8 dungeon adventure: White Plume Mountain. (Tales From the Yawning Portal).