Areas of Effect on a Grid
The Dungeon Master’s Guide includes the following short rule for using areas of effect on a grid.
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.
That rule works, but it can require a fair amount of on-the-spot adjudication. This section offers
two alternatives for determining the exact location of an area: the template method and the token
method. Both of these methods assume you’re using a grid and miniatures of some sort. Because
these methods can yield different results for the number of squares in a given area, it’s not
recommended that they be combined at the table — choose whichever method you and your
players find easier or more intuitive.
Template Method
The template method uses two-dimensional shapes that represent different areas of effect. The
aim of the method is to accurately portray the length and width of each area on the grid and to
leave little doubt about which creatures are affected by it. You’ll need to make these templates or
find premade ones.
Making a Template. Making a template is simple. Get a piece of paper or card stock, and cut it in
the shape of the area of effect you’re using. Every 5 feet of the area equals 1 inch of the
template’s size. For example, the 20-foot-radius sphere of the fireball spell, which has a 40-foot
diameter, would translate into a circular template with an 8-inch diameter.
Using a Template. To use an area-of-effect template, apply it to the grid. If the terrain is flat, you
can lay it on the surface; otherwise, hold the template above the surface and take note of which
squares it covers or partially covers. If any part of a square is under the template, that square is
included in the area of effect. If a creature’s miniature is in an affected square, that creature is in
the area. Being adjacent to the edge of the template isn’t enough for a square to be included in
the area of effect; the square must be entirely or partly covered by the template.
You can also use this method without a grid. If you do so, a creature is included in an area of
effect if any part of the miniature’s base is overlapped by the template.
When you place a template, follow all the rules in the Player’s Handbook for placing the
associated area of effect. If an area of effect, such as a cone or a line, originates from a
spellcaster, the template should extend out from the caster and be positioned however the caster
likes within the bounds of the rules.
Diagrams 2.1 and 2.2 show the template method in action.