What space does the spell Cloud of Daggers fill?

Question

I am trying to workout what template cloud of daggers (PHB, p. 222) would be on a grid. The spell states:

You fill the air with spinning daggers in a cube 5 feet on each side, centered on a point you choose within range.

So does that mean it would look like this:

Or like this:

From what I've read online, there seems to be some suggestion that it is a single square (tile) though this does stack with the spell description of "a cube 5 feet on each side".

Clearing this up for my group would be great, and I am sure our DM will be pleased as his monster were nicely diced by this spell. Thanks.

Answer 1

Cloud of daggers fills one 5-foot square.

Neither of the options that you show are correct. The spell description states that it takes up:

a cube 5 feet on each side

Since one square is five feet by five feet, you can fill one square with the cloud. If you target the center of a grid cell, then the spell fills that entire grid cell.

Note that the spell does not have a 5 foot radius. "5-foot radius" and "a cube 5 feet on each side" are very different measurements. A spell with a 5 foot radius fills a circle 10 feet wide. A spell that fills a cube 5 feet on a side fills a square, and that square is only 5 feet wide.

Answer 2

Cloud of Daggers only effects one tile if we assume everything "snaps to grid."

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What is "a cube 5 feet on each side?"

Looking at the section of the PHB "Areas Of Effect" we see:

Cube

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. A cube’s point of origin is not included in the cube’s area of effect, unless you decide otherwise. - PHB pg.204

In a comment you said:

The other way to look at it is if a point can have a side then it - spell has a 5ft radius. This is why I have asked this question.

Which suggests you are thinking of spheres and cubes as being similar areas of effect. When we're dealing with a 5 foot cube, there is a sphere that could be considered to be almost identical in effect, but it would have a 2.5ft radius, or a 5ft diameter. Of course, when the areas we're dealing with get bigger, the similarities decrease.

Take the image below:

The point indicated is at the center of both the cube and the sphere, and the length of one side of the cube is equal to the length of the diameter of the sphere (but the radius is only half that). While the sphere fits entirely inside the cube, there is plenty of space taken up by the cube that lies outside of the sphere's bounds. When using a 5ft grid, as the sphere/cube get larger, more and more spaces are effected by this difference, which is why I said "the similarities decrease."

If we were to say that the cube is 5 feet on each side, it would fit nicely inside one 5ftx5ft tile on a map. The area of effect of the sphere and the cube would be effectively the same if we consider that everything snaps to a grid: either one would completely effect one creature, and only one, as creatures can move through eachother's space, but not stay there.

How does this effect Cloud of Daggers?

As you said, the spell states:

You fill the air with spinning daggers in a cube 5 feet on each side, centered on a point you choose within range. - PHB pg.222

Usually you select the point of origin, which can be included in the effect or not, but in this case we select the center point, which must be within the area of effect. From this, we can see that a cube 5ft on each side could fit perfectly within one tile of a 5ft grid.

Again, in a comment you said:

we play with the notion that when you select a point you are select a square rather than a location on the grid which could cross into another square or in the middle of two.

Which sounds like snap-to-grid, so you couldn't place the cube on the intersection of two tiles as addressed by this question.

In conclusion:

Cloud of Daggers only effects one tile if we assume everything "snaps to grid."

Answer 3

Cloud of Daggers always affects four 5' squares.

The square takes the following area on a grid:

Image 1: Cloud of Dagger in blue, affected squares in red.

From the rules as written, it cannot take any other shape on the grid.

First, from the DMG page 251, regarding areas of effect:

Choose an intersection of squares or hexes as the point of origin of an area of effect, then follow its rules as normal.

The origin of the Cloud of Dagger spell must be an intersection of squares.

Additionally, from the description of the spell:

You fill the air with spinning daggers in a cube 5 feet on each side, centered on a point you choose within range

Hence the square is centered on its point of origin - which means it occupies the four squares around an intersection of squares.