Area of Effect

[Coranhann]

Hello everyone,

Context:
I usually DM without relying on battle maps (for various reasons I'd rather not go into).

My players are in a dungeon where they are facing groups of 8 monsters. In this case, I break my rule and use a battle maps.

One player uses a spell with a 10' cube AoE.

He places it at the center of a scare, so it affect 9 squares, instead of 4 squares, as a 10' cubes would if you targetted the intersection of square lines.

I'm all to let my players get away with small optimizations such as this, as I break/prevent the worst ones...
... but I wonder : Nothing in the rules of magic states that the point of origin of a cube should be at a cross, right ?

[Ninja_Prawn]

Nothing in the rules of magic states that the point of origin of a cube should be at a cross, right ?

No, and when you're using TotM, you'd imagine the spell's position could be anywhere at all, on an infinite, analogue scale. On a grid, I'd argue that the whole point of the grid is to simplify things like creature and spell placement. If you're going to buy into the 'grid' abstraction, you have to accept that spell placement is now discrete and restricted.

[Pex]

Is it a 10 ft radius or 10 ft diameter area of effect? There's a difference.

Also, while I'm away from book to double check the actual rule, in truth don't worry about it. It's a player thing to want to be efficient in spell use. Just let them. It's ok if the bad guys do it too. It's the game part of a role playing game. For in character justification, the characters know more about their abilities than the players do. They have an understanding of how their spells work. Metagame pin point accuracy is that representation of the characters knowing what they're doing with their abilities in world.

As for my personal experience in the matter, whether the center point is a corner or the middle of a square has always been player choice. It's done to get the most enemies as possible without hitting party members. The players have fun with it, and it never broke the game. It enhances tactical thinking and teamwork play.

[nickl_2000]

I pulled up the spell area descriptions and didn't see anything in there saying it had to be on a grid. It shouldn't matter as long as the bad guys get to place in the middle of a square on the grid as well as the PC

[Naanomi]

If I make people stand on the grid, then I make effects snap to the grid.

Usually though I let people move 'free form' without counting squares (I use string to measure the distances of movement and the like), and in such situations I allow AoE placement wherever they want (within reason, and AoEs that emanate from your body come from the center of 'your square' not the edges and the like)

[Contrast]

My personal preference is to not use a battle mat and just measure if you're using models, which moots the issue entirely. If you are using a battle mat though, I would insist on using the battle mat otherwise why are you using it. If you're happy for someone to cover half a square with a spell or stand straddling two squares there honestly doesn't seem any point in using the battle mat at all (or rather - feel free to use it as a surface you can draw on but just ignore the grid).

If you want to use the grid but offer players some flexibility and are concerned about balance you could maybe make it so that those 'half' covered get advantage on whatever saving throw the spell offers. Obviously let the players know about this when they're choosing how to position the spells if you do go down this route.

[Coranhann]

Thanks for your answers guys ! Ok, so nothing said about this.

I do agree with Ninja & Contrast, it makes sense to have AoE match the grid when I use battle mat...

... but as I said, I don't mind it too much. They don't go power gaming, so they can get away with it (and, as Pex said, I can do it too).

Rest of the time, when there is not that many monsters, I describe the position of the bad guys between the players, and decide how many can be affected by AoE, so I think it's fair to let them optimize when they can. Make them feel good.

But I was puzzled by the fact that I couldn't find any rule reference on this matter. Thanks to you, I know that it's not me missing a rule. Thanks again :)

[clash]

The way I handle it, is if the aoe would only affect half of the square an enemy is in then they get advantage on their save, as it is easier to avoid.

[Millstone85]

Is it a 10 ft radius or 10 ft diameter area of effect? There's a difference.If the area of effect is a cube, then it is actually 10 ft on a side. It is a 10' by 10' by 10' cube.


Nothing in the rules of magic states that the point of origin of a cube should be at a cross, right ?The rule actually exists.
Areas of Effect
The area of effect of a spell, monster ability, or other feature must be translated onto squares or hexes to determine which potential targets are in the area and which aren't.
Choose an intersection of squares or hexes as the point of origin of an area of effect, then follow its rules as normal. If an area of effect is circular and covers at least half a square, it affects that square.

[Coffee_Dragon]

He places it at the center of a scare, so it affect 9 squares, instead of 4 squares, as a 10' cubes would if you targetted the intersection of square lines.

I tend to think this kind of thing is confused at best, though I'll take your word for it that the player is not a powergaming munchkin. What's happening here is that the player accepts the parts of the abstraction that he can use - I get an AoE box this big, there's one target per map square - and dismisses another - AoE squares corresponding to map squares. But selectively blurring parts of an abstraction package deal doesn't necessarily lead a better simulation, and in this case it's pretty clear that shifting the AoE to (partially) cover more squares twists the intent of a system which already has the net effect of empowering players compared to Theatre of the Mind.

While it may seem reasonable on the face of it that NPCs would get to do it too, first, it's still probably a net gain for the PCs if there's at least one full caster, and second, it would generally empower casters, and they don't need boosting.

[Sigreid]

If you want to forget the grid all together the DMG has an equation for TOM to calculate how many beings are caught in the AoE on average.