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! 😊