That's no moon - how many size steps to reach moon-sized creatures/objects

[Greywander]

You might have seen me talk about this a few times, but the way the size system seems to be set up, each step up increases you size by the square root of 2 (~1.41) in every direction, or doubling your size every 2 steps. The exception to this is the jump from medium to large, which skips a step and doubles your size in one step. This also holds true for small creatures, which should be about 3.5 feet, however since you can't fit more than one small creature in a 5-foot square it seems they just rounded it up to 5 feet. One step down from 3.5 feet is 2.5 feet, which matches tiny.

In theory, you should be able to extend the list of size categories up or down indefinitely. I was curious how many extra steps you'd need to get to moon-sized creatures or objects, e.g. for handling things like ships/airships/spaceships (many of which will be larger than gargantuan) or eldritch horrors that lurk in the depths of space (which may be larger than a galaxy). Moon-sized seems like a good middle ground between the two. So I plugged the numbers into a spreadsheet to see how many steps you'd need.

The answer is that you need roughly 38 size steps above gargantuan to get something slightly smaller than the Moon. The Moon has a diameter of 2159 miles, or about 11,399,520 feet. A gargantuan+38 creature occupies a 10,485,760-foot square.

While neat, it's definitely not worth the effort to write up a full size table, with individual names for each size category. I think a simpler solution would be to (a) note the formula, so that players/DMs can calculate unlisted size categories themselves if they need to, (b) add a rank system to the list of sizes, such that medium is 1, and each step up increases the size rank by one, while each step down instead goes to 1/2, 1/3, 1/4, etc., and (c) give special names to specific sizes that are important, and note their size rank so that players can determine where it fits. For example, we might have a special "lunar" size that is size rank 43 (i.e. 42 steps above medium, with the missing size between medium and large). (Alternatively, size ranks could start at 0 for medium, and go negative for smaller sizes. That way, a size rank of 5 would mean 5 steps above medium, or medium+5. That might be easier.)

In practice, this only ever really matters when you have two creatures/objects that are similar sizes. Anything that vastly larger than your medium sized character may as well be gargantuan regardless of how big it actually is, which is why the size list only goes up that high in the first place. If you're controlling a massive ship that is gargantuan, then you might care about a sea monster that is a size or two above gargantuan. Basically, anything more than three sizes larger or smaller than you or whatever vessel you may be piloting doesn't really matter (most of the time), and may as well just be whatever the largest or smallest listed size is.

[Segev]

There also comes a point where the size difference is such that the larger creature is essentially terrain. Which probably could use some rules write p, now that I think about it.

[Anonymouswizard]

There also comes a point where the size difference is such that the larger creature is essentially terrain. Which probably could use some rules write p, now that I think about it.

I can see the use in some systems, a science fiction game where the players are in command of a medium sized ship for instance, but you'd probably scale things up by a factor of 10 or so in each step just to stop you from having to deal with 50 different size classes. But yeah, at this point the massive creature can't meaningfully target our platonic human (who is, of course, a perfect cube five feet on a side) while our human has little that'll hurt the moon sized creature.Unless the PCs have access to a ship at least a mile in length the scale differences probably round out to an eternal stalemate.

Although there are some instances I might treat a planet as a creature, if PCs were playing around with asteroid impacts or the like. But we're still scaling so far out of what most systems are designed to handle (but which there's probably a GURPS supplement covering).

[Imbalance]

As a minis guy, I haven't been afraid to adjust creature:map scale to imagine something that still occupies the bounds of surface-bound combat - that's why there's a grid. Players can adjust to the chess-like abstract to imagine that instead of normally moving six squares, you only move one to represent your full movement, and ranges are also proportionally truncated because in order to convey the sheer size of this threat each square represents ~25'. This is especially useful for vehicle combat, because then you can use a 4" toy boat instead of a $200 "miniature" ship vs a kraken to illustrate just how screwed they are.

I think if you're scaling to the planet-to-planet vs party disparity, or the likes of dealing with unfathomable eldritch horrors, or slaying gods in their own planes, that's theatre of the mind territory that the size rules aren't going to be adequate no matter what. Other games that center on combat for combat's sake have done as Segev said well enough: HeroClix' Krakoa map shows part of an island with a face in the middle that has special rules for random earthquakes or attacking plants, a concept I'll be stealing at some point even if I don't actually use a map. If we ever end up in a Spelljammer adventure, I've already planned to cop Attack Wing's rules for any ship-to-ship fights in the absence of anything officially covering it because it makes more sense than bothering to math the position of half a dozen medium characters on the deck of a magical vessel somewhere in the Phlogiston.

[Segev]

While we're on the subject, it kinda bothers me that storm giants are listed as "Huge" in the 5e monster manual. They're 26 feet tall. If they're half that wide at the shoulders, that's 13 feet wide. They barely fit inside a square 15 feet on a side, and tower over the top of the cube so represented. Compare a human or half-orc who is six to seven feet tall (still towering over a five foot cube) and 3 feet or so at the shoulders. That at least gives them some room to move inside a five foot square. Meanwhile, a hill giant is barely as tall as his 15 foot cube, but is also Huge.

[PhoenixPhyre]

While we're on the subject, it kinda bothers me that storm giants are listed as "Huge" in the 5e monster manual. They're 26 feet tall. If they're half that wide at the shoulders, that's 13 feet wide. They barely fit inside a square 15 feet on a side, and tower over the top of the cube so represented. Compare a human or half-orc who is six to seven feet tall (still towering over a five foot cube) and 3 feet or so at the shoulders. That at least gives them some room to move inside a five foot square. Meanwhile, a hill giant is barely as tall as his 15 foot cube, but is also Huge.

To be technical, the sizes are base area, not cubes. The third dimension isn't stated. But yes, there's some oddness in there.

As to the OP: zero. Gargantuan is already unbounded above, just like Tiny is unbounded below. Not a very satisfying answer, but that's the system's answer.

[Segev]

To be technical, the sizes are base area, not cubes. The third dimension isn't stated. But yes, there's some oddness in there.

As to the OP: zero. Gargantuan is already unbounded above, just like Tiny is unbounded below. Not a very satisfying answer, but that's the system's answer.

Yeah, I acknowledge that it's 2D. The issue with the Storm Giant is less the height, and more the breadth of shoulders compared to that base area.

[PhoenixPhyre]

Yeah, I acknowledge that it's 2D. The issue with the Storm Giant is less the height, and more the breadth of shoulders compared to that base area.

True. And that's not the only one. Although if we're only worried about space taken up within 5' of the ground (a guess based on the 2d-nature of size categories and the height of most PCs), then the fact that they're outside their area (or barely fit) up at 20+ feet isn't so bad....but I don't think that's the real case here.