For the Dungeon of the Mad Mage adventure, how is a room's ceiling height determined?

Question

As a player I am playing in the Dungeon of the Mad Mage adventure. On page 11, it describes how to determine ceiling height for rooms:

A room's ceiling is at least as high as the room is wide, often higher. If a room's ceiling isn't specified in the text, assume it's the minimum height.

What dimension do we use to figure this out? For example: a room is 30 feet (N-S) by 40 feet (E-W), with a door on the North wall and a door on the West wall.

Would this room be 30 feet or 40 feet "wide" (and thus 30 feet tall)? Assume the room height is not otherwise specified.

What if the room is odd shaped?

Answer 1

Assumption: The question is actually "How can I determine the height of a room where the height is not explicitly stated and the room is an irregular shape?"

Unfortunately, ask the DM

Often, a room's height doesn't matter. Many DM's (myself included) forget about ceilings until it actually comes up in play.

But if you're a connoisseur of ceilings, a renaissance-man of roofs, or a tourist of tops, you'll likely keep an eye out for such details, in case it comes in handy.

Matt Vincent has an excellent answer about "normally" shaped rooms, but in any case where "length" and "width" aren't easily measurable ('s' shaped rooms, '@' shaped rooms, 'etc' shaped rooms, etc.), you're just going to have to ask the DM.

Over time (Maybe before the end of the module), your DM will start learning to include that information, and you won't have to ask.

---

It may be worth noting that If you're trying to play a highly tactical game where the height of a room is critically important to your play style, you and your DM (or the other players) might not be all on the same page. A mini-session-zero revisit to address this could help out.

Answer 2

Width is the Shorter Side

According to 5e's lead designer: "Unless the rules explicitly expand, narrow, or completely redefine a word, that word retains the meaning it has in idiomatic English". What is "Width" in English?

• In geometry, length pertains to the longest side of the rectangle while width is the shorter side.
• Per Dictonary.com's definition of Length: "the measure of the greatest dimension of a plane or solid figure."
• Per Merriam-webster's definition of Length: "the longer or longest dimension of an object"
• Per the Wiktionary's definition of Length: "The distance measured along the longest dimension of an object."
• Per the Wikipedia entry for Length: "Length is commonly understood to mean the most extended dimension of an object."

These standard definitions are consistent with how the terms are used in the rule books. Examples:

• An ankheg "spits acid in a line that is 30 feet long and 5 feet wide"
• A Black pudding or Air Elemental "can move through a space as narrow as 1 inch wide"
• A Black Dragon "exhales acid in a 90-foot line that is 10 feet wide"
• The Gust of Wind spell creates "A line of strong wind 60 feet long and 10 feet wide"

If you are concerned that the writer's accidentally misused the word, their intent seems be backed up with:

• A long, thin room (say 20'x100) is unlikely to have a tall (100') ceiling
• In Dungeon of the Mad Mage p.11: "assume it's the minimum height" would not lead one to use the longest side.

In Summary

Dungeon of the Mad Mage (p. 11):

A room's ceiling is at least as high as the room is wide, often higher. If a room's ceiling isn't specified in the text, assume it's the minimum height.

This indicates that a 30'x40' room would indeed be 30' tall, assuming the room height is not otherwise specified.

For oddly shaped rooms: the DM will have to make a call. I'd recommend approximating a rectangle that the room, or discrete sections of the room, would fit into. Example: a 30'x40' oval room with an adjacent 10'x10' alcove might have a 30' ceiling, except in the alcove (where it might have a 10' ceiling).