Emanation: radius or diameter?

Hi there, Midgardians!

So my question is regarding the size of an emanation. So when a spell says: "a 30ft emanation", is it talking about its radius or its diameter?

Thanks in advance.

It is the radius(-ish). While it doesn't use that word, specifically, the definition of an emanation and a radius are basically identical.

That said, it extends from all of the occupied squares, so a large creature with a 10ft emanation would basically cover a 6x6 area (excluding itself if it wants).

Quote from sabin76 >>

It is the radius(-ish). While it doesn't use that word, specifically, the definition of an emanation and a radius are basically identical.

That said, it extends from all of the occupied squares, so a large creature with a 10ft emanation would basically cover a 6x6 area (excluding itself if it wants).

Ok, thank you! 😊

For future reference, the Rules Glossary is a good source for answers like this: https://www.dndbeyond.com/sources/dnd/br-2024/rules-glossary#EmanationAreaofEffect

It's not quite radius (slightly smaller than the actual radius), because it extends from the creature or object, not a single point.  So a medium-sized creature casting a 30' emanation (with range self) would affect a 65' diameter sphere, because it extends from their space 30' in all directions.  If it was a large creature casting the same spell, it would end up with a 70' diameter ~sphere.

Quote from sabin76 >>

It is the radius(-ish). While it doesn't use that word, specifically, the definition of an emanation and a radius are basically identical.

That said, it extends from all of the occupied squares, so a large creature with a 10ft emanation would basically cover a 6x6 area (excluding itself if it wants).

 This is also my understanding, but for fairness, not the only opinion in the subforum, see e.g. Paladin Aura of Protection

I draw some examples in the past, like the following one using the Spirit Guardians spell:

And other threads with more examples in case they're helpful for anyone here or future visitors:

- Grid AoE Mechanics
- The behaviour of spell AoEs and Line spells when originating from larger creatures
- 2024 AOE changes
- Does Conjure Animals (2024) act like Spike Growth or like Spirit Guardians?
- 15 feet cone from above
- Dust disappearance aoe

(note: the drawings I make don't use the optional rule in the DMG about diagonals on a grid, where range is measured differently)

FWIW, there is also this note in the DMG in Adjudicating Areas of Effect:

*Use this column for Cylinders, Emanations (using the size of the Emanation rather than its radius), and Spheres.

Quote from Tarod_ >>

Quote from sabin76 >>

It is the radius(-ish). While it doesn't use that word, specifically, the definition of an emanation and a radius are basically identical.

That said, it extends from all of the occupied squares, so a large creature with a 10ft emanation would basically cover a 6x6 area (excluding itself if it wants).

 This is also my understanding, but for fairness, not the only opinion in the subforum, see e.g. Paladin Aura of Protection

I draw some examples in the past, like the following one using the Spirit Guardians spell:

And other threads with more examples in case they're helpful for anyone here or future visitors:

- Grid AoE Mechanics
- The behaviour of spell AoEs and Line spells when originating from larger creatures
- 2024 AOE changes
- Does Conjure Animals (2024) act like Spike Growth or like Spirit Guardians?
- 15 feet cone from above
- Dust disappearance aoe

(note: the drawings I make don't use the optional rule in the DMG about diagonals on a grid, where range is measured differently)

Seeing this I have one question about it. What if the square is not fully covered by the area of effect? Would the creature in that square get the damage, for example?

Thanks in advance.

I follow this advice from the DMG:

Areas of Effect

An area of effect must be translated onto squares or hexes to determine which potential targets are in the area. If the area has a point of origin, choose an intersection of squares or hexes to be the point of origin, then follow its rules as normal. If an area of effect covers at least half a square or hex, the entire square or hex is affected.

Quote from Tarod_ >>

I follow this advice from the DMG:

Areas of Effect

An area of effect must be translated onto squares or hexes to determine which potential targets are in the area. If the area has a point of origin, choose an intersection of squares or hexes to be the point of origin, then follow its rules as normal. If an area of effect covers at least half a square or hex, the entire square or hex is affected.

Ok, thank you! 😊

Quote from Squirrelloid >>

It's not quite radius (slightly smaller than the actual radius), because it extends from the creature or object, not a single point.  So a medium-sized creature casting a 30' emanation (with range self) would affect a 65' diameter sphere, because it extends from their space 30' in all directions.

Technically, an emanation extends from the creature or object, not from the creature's space, and is thus actually (a) not clearly defined (rules generally say what a creature's space is, not what the size of the creature itself is), and (b) not necessarily a sphere.

Quote from Pantagruel666 >>

Quote from Squirrelloid >>

It's not quite radius (slightly smaller than the actual radius), because it extends from the creature or object, not a single point.  So a medium-sized creature casting a 30' emanation (with range self) would affect a 65' diameter sphere, because it extends from their space 30' in all directions.

Technically, an emanation extends from the creature or object, not from the creature's space, and is thus actually (a) not clearly defined (rules generally say what a creature's space is, not what the size of the creature itself is), and (b) not necessarily a sphere.

 Fair, but also unplayable.

Quote from Squirrelloid >>

 Fair, but also unplayable.

Only really becomes relevant if you do something like casting darkness on a rope. 

Quote from Pantagruel666 >>

Quote from Squirrelloid >>

 Fair, but also unplayable.

Only really becomes relevant if you do something like casting darkness on a rope. 

 What a sec... are you saying that you could cast darkness on a 50ft rope, and if the rope were stretched out to its fullest length then you would basically have a "tube" of darkness that is 15 feet high, 30 feet wide,  and 80 feet long (15 feet emanating from either end means an additional 30 feet to the rope, so 80 feet)?

Quote from MaximusArael020 >>

Quote from Pantagruel666 >>

Quote from Squirrelloid >>

 Fair, but also unplayable.

Only really becomes relevant if you do something like casting darkness on a rope. 

 What a sec... are you saying that you could cast darkness on a 50ft rope, and if the rope were stretched out to its fullest length then you would basically have a "tube" of darkness that is 15 feet high, 30 feet wide,  and 80 feet long (15 feet emanating from either end means an additional 30 feet to the rope, so 80 feet)?

 Technically you could get 30' high if you suspended the rope 15' in the air.

Technically, an emanation extends from the creature or object, not from the creature's space, and is thus actually (a) not clearly defined (rules generally say what a creature's space is, not what the size of the creature itself is), and (b) not necessarily a sphere.

And technically the only dimensional information we're given about creatures (and many objects) is their size category.

A creature or an object belongs to a size category: Tiny, Small, Medium, Large, Huge, or Gargantuan. A creature’s size determines how much space the creature occupies in combat. An object’s size affects its Hit Points. See also “Breaking Objects” and “Playing the Game” (“Combat”).

Thus either

• All creatures are zero-dimensional points in space

or

• Size category is what you use for determining size-relevant information such as how to measure the reach of an emanation.

Emanations are very clearly measured based on creature (or object) size category and to argue otherwise is disingenuous 

Quote from MaximusArael020 >>

Quote from Pantagruel666 >>

Quote from Squirrelloid >>

 Fair, but also unplayable.

Only really becomes relevant if you do something like casting darkness on a rope. 

 What a sec... are you saying that you could cast darkness on a 50ft rope, and if the rope were stretched out to its fullest length then you would basically have a "tube" of darkness that is 15 feet high, 30 feet wide,  and 80 feet long (15 feet emanating from either end means an additional 30 feet to the rope, so 80 feet)?

 Technically, that's what the rules say.

But I wouldn't expect most GMs to freely let you get away with shenanigans like the rope. (I'd probably reduce the emanation's size to 5 or even 2.5 feet.)

Quote from Davyd >>

Emanations are very clearly measured based on creature (or object) size category and to argue otherwise is disingenuous 

Arguments that start with 'technically' are almost always about RAW, not RAI. They could easily have written it as extending from an object or creature's space, they just didn't.

Quote from jl8e >>

Quote from MaximusArael020 >>

Quote from Pantagruel666 >>

Quote from Squirrelloid >>

 Fair, but also unplayable.

Only really becomes relevant if you do something like casting darkness on a rope. 

 What a sec... are you saying that you could cast darkness on a 50ft rope, and if the rope were stretched out to its fullest length then you would basically have a "tube" of darkness that is 15 feet high, 30 feet wide,  and 80 feet long (15 feet emanating from either end means an additional 30 feet to the rope, so 80 feet)?

 Technically, that's what the rules say.

But I wouldn't expect most GMs to freely let you get away with shenanigans like the rope. (I'd probably reduce the emanation's size to 5 or even 2.5 feet.)

 Really?  Is that any different than casting it on a huge boulder (~15' diameter) and measuring the emanation out from the boulder?

I would expect most GMs would let you make a tube of darkness out of a rope, because that's what the spell says.

Quote from Davyd >>

Technically, an emanation extends from the creature or object, not from the creature's space, and is thus actually (a) not clearly defined (rules generally say what a creature's space is, not what the size of the creature itself is), and (b) not necessarily a sphere.

And technically the only dimensional information we're given about creatures (and many objects) is their size category.

A creature or an object belongs to a size category: Tiny, Small, Medium, Large, Huge, or Gargantuan. A creature’s size determines how much space the creature occupies in combat. An object’s size affects its Hit Points. See also “Breaking Objects” and “Playing the Game” (“Combat”).

Thus either

• All creatures are zero-dimensional points in space

or

• Size category is what you use for determining size-relevant information such as how to measure the reach of an emanation.

Emanations are very clearly measured based on creature (or object) size category and to argue otherwise is disingenuous 

 I certainly agree on creatures, although I take it as a matter of practicality rather than RAW.  For objects that don't fill squares, we can use their actual dimensions or treat them as point sources pretty easily.  The dnd rope is a standard ~1" diameter rope of known length.  You can functionally treat that as a line for emanations.  If you cast Darkness on a pebble, that's basically a point source.

I'm not sure how many emanations there are that can target an object. There's darkness and daylight (oddly, light is not worded as an emanation)