How do we determine circular AoE areas on grid?

Question

I don't know how to explain it, but I have a question about spells areas, imagine a spell has a 10´radius circle area, which one work better?

I'm confused because the lower option its not 10´foot radius its, 12,5´foot radius, taking an extra square of area.

How do you calculate whether a square is part of the AOE? If you're going by 50% or more coverage by the actual circle, then the corner pieces in your second example would not be included, as they're (although close) a little under 50% covered. — PixelMaster, Mar 15 '20 at 10:24
You need to clarify the question. What does "work[s] better" mean? Be easier to implement at your table (if so there woule also be a difference between online, drawn grid and minature games)? Is "more correct" according to the rules? Something else? — fabian, Mar 15 '20 at 12:57
Related: "20 foot square versus a 20 foot circle on a battle mat" and "How many squares on a 5-foot grid does a 5-foot radius spell affect?" and "How to measure on a grid the area of a sphere area spell or effect centered on a creature?" — Exempt-Medic, Mar 15 '20 at 15:05

score 8 · Answer 1 · answered Mar 16 '20 at 02:37

Your first option is correct.

The origin of an AoE must be the intersection of squares, and squares that are more than half covered are affected.

DMG, p251:

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.

By that rule, a 10ft radius could also affect a 3x3 cell area, by placing the origin in the middle of the center cell, right? I.e., OP's second diagram, but excluding the N/E/S/W cells as they are not more than half-covered. — Cam Jackson, Feb 09 '24 at 09:42

How do we determine circular AoE areas on grid?

1 Answers1

Your first option is correct.