If a paladin becomes Large, at what point does the paladin's aura originate?

Question

If you enlarge a paladin (so that they take up 2×2 squares on a grid), what point does their aura's radius start at?

For Medium/Small creatures (who take up a 1×1 square on a grid), it radiates from one of the corners of the square. For Large creatures, is it still at one of the corners of the 2×2 square, at the intersection at the center of one of the sides of the creature's space, or at the intersection at the center of the creature's space?

Additional info:

• According to the designers, the point of origin of a spherical area of effect is at the intersection of squares on a grid.
• According to Mike Mearls, paladin auras work the same way.

Answer 1

Paladin auras "originate" from their entire space, so the radius extends from the edge of their space

In this case, Mike Mearls' interpretation in your second link is incorrect, in addition to not being an official ruling (which is good, considering Mearls' tweets rarely have any basis in the rules).

All of the paladin auras don't specify a "point" of origin; instead, they merely specify that certain effects apply to creatures "within 10 feet of you". (At 18th level, the range of your auras increases to 30 feet.) In essence, it's an "area of origin" rather than a single point.

For instance, the description of the paladin's Aura of Protection feature states:

Starting at 6th level, whenever you or a friendly creature within 10 feet of you must make a saving throw, the creature gains a bonus to the saving throw equal to your Charisma modifier (with a minimum bonus of +1). You must be conscious to grant this bonus.

And the description of the Aura of Courage feature says:

Starting at 10th level, you and friendly creatures within 10 feet of you can’t be frightened while you are conscious.

(Most of the subclass options also grant their own auras at 7th level.)

Logically speaking, it would make no sense to say that a creature right next to a Large or Huge creature is not "within 10 feet of it". Thus, an aura is an effect that does not have a point of origin; it originates from you and your space as a whole.

Rules designer Jeremy Crawford addressed a question about the area/range of a 10-foot paladin aura in this pair of unofficial tweets from March 2016:

Which is correct representing the area of paladin aura (10 ft)?

Is each square 5 ft., and which aura are you talking about?

Yes, each square is 5 ft. I meant Aura of Protection and Aura of Courage. Thanks.

Aura of Protection/Courage extends 10 ft. all around. (None are correct, unless your circles are polygons.)

In that example image:

• option A treats the aura as if it originates from the center of the creature's space
• option B treats it as if it were a spell, originating from a corner of the grid adjacent to the creature
• option C treats it as if it extends from the edge of the creature's space, but inaccurately depicts the circular aura

Crawford's response suggests that C is the closest to being correct, but is wrong because of the way it depicts the area of the aura as a polygon instead of a circle.

(Also, even if the DM did decide to have the aura be square instead of circular since they're playing on a grid, the diagonals in C are too short.)

This interpretation is further supported by Crawford's reasoning in this series of unofficial tweets from May 2018 as to why the centaur and minotaur playable races (originally released for playtesting in Unearthed Arcana: Centaurs and Minotaurs at the time) should mechanically remain Medium like all other playable races instead of Large:

Visualizing one of @JeremyECrawford's reasons why Centaur and Minotaur should not be Large PCs: a 5' aura is 50% bigger and a 10' aura is 33% bigger.

That's exactly right.

Is it safe to assume we shouldn’t expect Large PC races?

Yep.

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In short: Paladin auras extend from the edge of the paladin's space, not from any individual point.

For a Medium creature, a 10-foot aura is a circle over a 5×5 area on a grid (with 5-foot squares); for a Large creature, that same aura is a circle over a 6×6 area on the grid.

Answer 2

The aura's origin is your character and the space(s) they occupy.

Say for instance you are talking about Aura of Protection, and the Paladin was enlarged by an enlarge/reduce spell, they would occupy 2x2 squares of space.

Since their own body is the source of the aura, they are affected by it as well as every ally within 10ft of them.

D&D relying on a grid representation, and each square by default being 5ft, their aura, in Large state of 2x2 squares, would be of 6x6 squares which represents a 10ft radius around them.

If you were to do the sum of squares affected by the aura in Medium vs. Large state, including the paladin themself, you would have:

• Medium size (1x1): 10ft Aura = 5x5 (25 squares) with the center 1x1 square being the origin so effectively 24 squares of potential allies affected.
• Large size (2x2): 10ft Aura = 6x6 (36 squares) with the center 2x2 squares being the origin so effectively 32 squares of potential allies affected.

To sum it up, the aura will affect allies within 10ft of the squares occupied by the source.