How is the power of a magic item measured according to the rules?

Question

Premise

The DMG states a relation to a magic item's power, it's rarity, and character level.

Rarity provides a rough measure of an item's power relative to other magic items. Each rarity corresponds to character level..

It follows up immediately with an example

A character doesn't typically find a rare magic item, for example, until around 5th level.

Question

The rules seem to have some sort of definition of what power means. What is it?

Rationale

A number of questions seem predicated on estimating the power of a magic item. E.g:

• Is item rarity really tied to how powerful it is?

• How can I balance the power of loot between players?

Answer 1

On DMG p. 285, in the "Power Level" portion of the "Creating a Magic Item" section, there is a brief discussion of how two measurable levels of power (spell level and static bonus) relate to rarity.

That brief section includes this table:

Magic Item Power by Rarity

\$\begin{array}{|l|c|c|} \hline \textbf{Rarity} & \textbf{Max Spell Level} & \textbf{Max Bonus} \\ \hline \text{Common} & \text{1st} & \text{—} \\ \text{Uncommon} & \text{3rd} & \text{+1} \\ \text{Rare} & \text{6th} & \text{+2} \\ \text{Very Rare} & \text{8th} & \text{+3} \\ \text{Legendary} & \text{9th} & \text{+4} \\ \hline \end{array} \$

But beyond this table there isn't really any other concrete discussion of power level being linked to rarity.

There is also a brief discussion about attunement, but nothing much beyond how it should be used as a tool to prevent abuse. This implies that lack of attunement increases an items power level.

The discussion in the DMG is however combat focused, and as such doesn't consider the social or exploratory pillars of the game.

Answer 2

It's not clear

The rules do not clarify exactly how "Power" is measured relatively. They also do not seem to provide a methodology that can be used to look at the known examples of items and figure out what was used to determine their "power rating".

Without either an explicit or implicit mechanic for measuring "Power", it is left as an unknown. That's not helpful for us as community in trying to figure out how to measure a homebrew item or a change in an existing item, but it does seem to be the reality of the situation.

Until we have a clear methodology, we are left making the judgement calls ourselves based on our players, our worlds, and our tables.

Answer 3

Regarding the "Magic Item Power by Rarity" table (DMG, p. 285) referenced in illustro's answer, I have found that magic items add rarity to increase their frequency of use or range of effects. So, a good set of rules of thumb are:

1. Once per day is the base rarity
2. A charged item regains d3-d6 +1 charges per day at a cost of one rarity higher than the spell that created it
3. An 'at-will', or continuous effect, item produces a magic item that is two rarity levels higher than its originating spell
4. If the spell requires Concentration, then the magic item typically requires attunement
5. If it has multiple effects then increase the rarity by at least one more level, unless it has a self-destruct mechanism, like several Staffs with multiple spells.

For example:

• A charged wand of Magic Missile (L1) is Uncommon
• A charged wand of Polymorph (L4) is Very Rare and requires attunement
• An 'at-will' Ring of Featherfall (L1) is Rare and requires attunement
• A charged Staff of Frost has multiple spells, with Wall of Ice (L6) as it's highest level spell, but can be destroyed by overuse, so it's Very Rare.

Finally, if the result is overpowered then the rarity is probably one higher, e.g. Ring of Invisibility (L2) is Legendary, not Very Rare. And if it only gives a bonus to a single ability check, or other limited effect, then it's probably one rarity lower, as with the 'at-will' Ring of Jumping (L1), which is only Uncommon, not Rare as we might otherwise expect.

Obviously, this method isn't perfect or complete, but I do find it to be a useful heuristic for building custom magic items. Hopefully that helps!

Answer 4

It could also be tied to the "level" of the adventurers. A farmer that picked up a sword to fight to local riff raff (level 0 / Commoner) probably isn't rocking a +3 longsword. But, a seasoned Dungeoneer who has taken down all manner of beasts, beholders, and beguiled is more likely to find that sort of thing in their time out and about. As the overall status / level / power of the PC increases so does their likely rewards or found loot.

This idea is in the DMG and the PHB