[RPG] difference between cube areas-of-effect with Self or 5-feet ranges


To cast cube-shaped spells,

You select a cube's point of origin, which lies anywhere on a face of the cubic effect.

After looking through a multitude of other questions regarding Thunderwave (see 1, 2, 3), which has a range of self, it seems to be general consensus that you can cast Thunderwave as the picture below shows.

enter image description here

But the thing is, this means you have a range of 5ft for casting it, doesn't it? Your point of origin is the square 5ft in front of you. I just assumed that a range of self meant something like this.

enter image description here

You wouldn't take damage since:

A cube's point of origin is not included in the cube's area of effect, unless you decide otherwise.

In order for both these images to be possible casts of Thunderwave, a range of self and a 5ft are the same. Is this interpretation correct?

PS: I didn't show the cube to have 15ft height, but that's to keep things simple. Assume the cube has the proper height, but for this question, we are focusing on the bottom third of it.

Best Answer

Yes, there is a difference

Or rather, No, your interpretation is incorrect.

First of all, let's look at the rules really quick.

Area of Effect on a Grid, DMG (I don't have the DMG in DnD Beyond, so this excerpt is from Xanathars)

Choose an intersection of squares as the point of origin of an area of effect, then follow the rules for that kind of area as normal (see the “Areas of Effect” section in chapter 10 of the Player’s Handbook). If an area of effect is circular and covers at least half a square, it affects that square.

So by the very nature of using a grid template, you're bound by the rules of choosing an intersection as the point of origin. Your character sits at the center of a square and occupies the entire square. The edges and corners of your square are 0 feet. The next square over, those far edges are all 5 feet away (including diagonals). Similarly, most characters have a melee reach of 5 feet which extends out towards the adjacent 8 squares. When creatures move out of those tiles, opportunity attacks are provoked. Range is always calculated from your tile boundary outwards and excludes the tile that the edges the range touches belong to. So 5 feet from your edge is another edge, but it excludes the next tile over. In this way, you can count the squares in a typical 5-foot grid system to calculate range.

So, a range of self is actually the "5-foot" range image you posted, since you are choosing a corner 0 feet away. If you had a 5-foot range, you could choose the intersection of any square up to 5 feet away, effectively moving the effect one tile away from yourself.

Remember that your point or origin is not always centered on a face of a cube, but rather anywhere on any face of that cube. So you must always pick a corner as the origin, but you could "translate" that cube any way you'd like.

Areas of Effect, Cube, PHB

You select a cube's point of origin, which lies anywhere on a face of the cubic effect. The cube's size is expressed as the length of each side.