D&D 5th Ed. and geometry

[Kitilark]

I finished High school before calculators, and though it says Algebra on my transcripts my grandchildren took the same stuff in Middle School. I never did learn to use a slide-rule. So here is my question: How Big is a 15-foot cube? I have been told it is a 5-foot by 5-foot by 5 foot area; 5' high, 5' wide, and 5' long. But when I took math (I hope they still call it that) I was taught that a cube was the word assigned to 'the power of 3'; as in 15 cubed is 15x15x15; or 15' high, 15' wide and 15' long; or 15 raised to the power of 3.

Here is one place it applies: If the first answer is correct and it is 5'x5'x5' why would a spell only reach 5' off the ground? and yet effect things to a distance of 10 feet well past it's width and length?

Range Self (15-foot cube)

A wave of thunderous force sweeps out from you. Each creature in a 15-foot cube originating from you must make a Constitution saving throw. On a failed save, a creature takes 2d8 thunder damage and is pushed 10 feet away from you. On a successful save, the creature takes half as much damage and isn't pushed.

In addition, unsecured objects that are completely within the area of effect are automatically pushed 10 feet away from you by the spell's effect, and the spell emits a thunderous boom audible out to 300 feet.

Thanks, if I can understand this one the rest should follow the same rules - unless math has really change.
Kitty

[Zacchaeus]

A 15' cube is a box 15' on all sides; so yes 15'x15'x15'. 5' on a side would be a 5' cube.

[LordEntrails]

But, 15 cubic feet can be encompassed by a rectangular solid that is 5ft x 5ft x 5ft.

Note, 15 cubic feet is different from a 15 foot cube :) (a 15 foot cube contains 3375 cubic feet!)

[JohnD]

I don't know what kind of math they're teaching today. Now 2+2+2 = approximately 7 is the right answer and 6 is marked incorrect.

[Kitilark]

But, 15 cubic feet can be encompassed by a rectangular solid that is 5ft x 5ft x 5ft.

Note, 15 cubic feet is different from a 15 foot cube :) (a 15 foot cube contains 3375 cubic feet!)

So, if a spell ever reads: Range 15 cubic feet
it would be a solid block of "magic" dropped on a target.
Good to know.
Kitty

[jshauber]

I don't know what kind of math they're teaching today. Now 2+2+2 = approximately 7 is the right answer and 6 is marked incorrect.

Don't they at least get half credit for spelling their name correctly whether they answer any questions of not?

[LordEntrails]

Don't they at least get half credit for spelling their name correctly whether they answer any questions of not?
No, but they get a trophy.

[damned]

But, 15 cubic feet can be encompassed by a rectangular solid that is 5ft x 5ft x 5ft.

Note, 15 cubic feet is different from a 15 foot cube :) (a 15 foot cube contains 3375 cubic feet!)

Technically you are correct LordEntrails but I think you are confusing people...
Whilst a 5'x5'x5' cube would encompass 15 cubic feet it actually encompasses 125 cubic feet - it uses the same math that you used to come up with 3375...
Just sayin... :)


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[Kitilark]

Range Self (15-foot cube)
A wave of thunderous force sweeps out from you. Each creature in a 15-foot cube originating from you must make a Constitution saving throw. On a failed save, a creature takes 2d8 thunder damage and is pushed 10 feet away from you. On a successful save, the creature takes half as much damage and isn't pushed.

In addition, unsecured objects that are completely within the area of effect are automatically pushed 10 feet away from you by the spell's effect, and the spell emits a thunderous boom audible out to 300 feet.


For 100 points or an A+
Using a Fantasy Grounds Map with 5 foot grid; what is the Range of the above spell? Be specific.

[damned]

Your square plus one square in every direction.

[Kitilark]

15505 damned's answer.

so this spell is a really close range attack.

and can not be used like this?
15506

[Trenloe]

From the D&D Basic Rules (page 81): [
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.
So, in post #11 above, the second image is correct. You could also shift it 5 foot left/right and place it on any of the other three faces of the "S" token.

[Trenloe]

Also see the info in the Fantasy Grounds 5E PHB reference manual: Part 3: The Rules of Magic -> Casting a Spell -> "Areas of Effect" section. This includes a "Point of Origin" image (from the PHB) and has the same text as from the basic rules.

[LordEntrails]

Technically you are correct LordEntrails but I think you are confusing people...
Whilst a 5'x5'x5' cube would encompass 15 cubic feet it actually encompasses 125 cubic feet - it uses the same math that you used to come up with 3375...
Just sayin... :)

I used a calculator, not my brain. No idea what I did, but yea, 3375.. wtf?

[Nickademus]

Your square plus one square in every direction.

I have seen GMs do this, but this is not the way the cube area is described in the 5e PHB. The point of origin for a cube is in the center of one of the sides (unlike the sphere where to PoO is in the center). So thunderwave is a wave that starts at you and spreads out in one direction on the map.

15507

[damned]

Nickademus and Trenloe have both pointed to the specific info on this. It is a 15'x15' square and you can be placed at a point along one of the edges.

[Brynnan]

I got lost in everyone's answer. I don't know what they were all saying. lol.

The correct "D&D" answer is that the following are valid 15x15 cubes. The Caster can stand in any of the areas marked with the X and affect the areas marked with @ which is the damage/spell effect area. Basically, it affects the 9 blocks in front of you. (Your DM will hate you if you cast diagonally. But do it anyway.)

.....X.....
..@@@..
X@@@X
..@@@..
.....X.....

The alternative you are asking about of the following:

............
..@@@..
..@X @..
..@@@..
............

Would be typically be called a sphere or a cylinder centered on the caster. (Technically that would be a 7.5 ft radius; DMs will argue what other additional squares would be covered in a 10 ft radius spell effect.

Also, keep in mind that the confusion may be because Fantasy Grounds only reports it as a radius when you are drawing it on the map. So start your cube drawing in the middle of a grid square and drag out so that 9 blocks are highlighted. Then you can drag it into the position you want. Fantasy Grounds will have it listed as a 5' RADIUS cube. (which wouldn't hurt to get changed, guys. :) )

Also, Nickademus the PHB says the point of origin can be ANY of the [6] cube sides. And reiterates that by saying the point of origin isn't included in the cube, unless you decide for it to be. So you CAN center it on yourself. It's also noteworthy to mention it can be ANYWHERE on any face, it doesn't have to be a center of one of the sides. It just has to share an edge of the caster's 5x5 square (or 5x5x5 cube).

[Trenloe]

The correct "D&D" answer is that the following are valid 15x15 cubes. The Caster can stand in any of the areas marked with the X and affect the areas marked with @ which is the damage/spell effect area. Basically, it affects the 9 blocks in front of you. (Your DM will hate you if you cast diagonally. But do it anyway.)

.....X.....
..@@@..
X@@@X
..@@@..
.....X.....
Is there an official errata/update regarding this as the wording in both the basic rules and PHB says: "You select a cube's point of origin, which lies anywhere on a face of the cubic effect." It even goes on to say "A cube's point of origin is not included in the cube's area of effect, unless you decide otherwise." suggesting that the position of the point of origin is most certainly flexible. Based off this wording, unless there's been an official update on this, it appears that the written rules are in contradiction to the "* Point of origin" image in the PHB (a part of which is shown in past #15 above). Which, to be honest, I've always taken as an example not the only points of origin available - based off the written rules.

EDIT: Re-reading your post - does the "X" extend along the dots? If so, I agree. I was originally reading it as if the X was the only place for the point of origin - i.e. the middle of the side only?

[Brynnan]

No Errata, but yes. The caster can stand at any point around that cube. (Technically, he can't stand diagonally, but I don't know of any DM that would call him on that.) The wording is correct, so no errata is needed. The image is just a example of a point of origin, not the only option. It would be difficult to show all of them.

Also, I re-edited my post several times, make sure you are reading the final version. lol

[Trenloe]

Also, I re-edited my post several times, make sure you are reading the final version. lol
Haha, yeah I replied based off reading the email notification with the original diagram, not the end post. No worries! :)

[Brynnan]

Officially, the caster's square/cube has to share a side with the area of effect cube. But again, I don't know of any DM that would call them on a purely diagonal one. If he does tell them you turn diagonally to cast it. That will teach him. lol

[Brynnan]

Now, if FG could fix that whole 5' radius indicator nonsense for cubes/squares that would be great. ;) I understand that the cone angle is being fixed, so.... you know... we could hope?

[Kitilark]

Officially, the caster's square/cube has to share a side with the area of effect cube. But again, I don't know of any DM that would call them on a purely diagonal one. If he does tell them you turn diagonally to cast it. That will teach him. lol
Personally, I will be delighted if I can convince my GM(s) that a 15 feet cube really has 15 feet on each side ..... :D

[Trenloe]

Personally, I will be delighted if I can convince my GM(s) that a 15 feet cube really has 15 feet on each side ..... :D
I don't see why not, it's pretty clear in the PHB and Basic Rules - see post #12 above.

[Brynnan]

If he wants to discuss it, he can holler at me or another Adventure League LC. The DM League group on Facebook (https://www.facebook.com/groups/DMsLeague/) will be a good place for him to ask about it also.