Average weight for each size category?

[Greywander]

Someone else posted a thread about small creatures shoving large creatures, and it got me thinking about size categories, and specifically how much an average creature in each category would weigh.

I also noticed that there's an odd jump from medium to large, where large is twice as big as medium, whereas all other size increases (including from tiny to small, and small to medium) are by a factor of 1.41 (the square root of 2, or two steps is double the size). Because of this, each step in size should increase the weight by about 2.83 times, or by 8 times for every two steps.

As an example, if we assume an average medium creature weighs 200 lbs., then this would mean a large creature (who is double the size of medium) would weigh 1600 lbs, huge (1.41 bigger than large) would be 4525 lbs., and gargantuan would be 12800 lbs. Small would be 70.7 lbs., and tiny would be 25 lbs.

Doing a bit of research, horses can go up to 2000 lbs., or as low as 900 lbs. Cats (who would likely be one step below tiny, or 8.84 lbs average using the numbers above), range from 5 to 25 lbs., which sounds about right.

I'm a little unclear whether "size" is strictly space occupied (e.g. height, length), or if it also includes weight. Even if it's just the former, if we assume that most creatures have similar material composing their bodies, then they should have a similar density. Some animals, like birds with hollow bones, fish with gas-filled bladders that provide buoyancy, or animals with lots of fat like seals, will be lighter/less dense, while those with a lot of denser body material, like the armor plating of a pangolin, should be heavier.

The human body surprisingly has a density that is very close to water, which is about 62.4 lbs. per cubic foot. There are 125 cubic feet in a 5 foot cube, or 7800 lbs. if the entire cube is filled with water. Average human weight is around 150 lbs, or roughly 2% of the cube... Is my math right? This would mean that a human body only fills about 2% of the 5 foot cube they occupy, or that you could stack about 50 bodies in that volume.

If we use the value of 2% of the same volume of water, then we get the following weights for each size:

Tiny: 19.5 lbs.
Small: 55.2 lbs.
Medium: 156 lbs.
Large: 1248 lbs. (remember, large is twice the size of medium, all other size steps are only 1.41 times bigger)
Huge: 4212 lbs.
Gargantuan: 9984 lbs.

If these are the average weights, we can probably cut these values in half to get the minimum weights, e.g. 27 lbs. is either the biggest tiny creature or the smallest small creature, and medium sized creatures can go as low as 78 lbs. or as high as 624 lbs. (It's a bit awkward, since there seems to be a size missing between medium and large.) I'd probably round these off by manually setting the average tiny weight to 20 lbs. instead of 19.5, which would make the average medium weight 160 lbs., average large 1280 lbs., and average gargantuan 10240 lbs.

Anyway, a list of average weights for each size category would be useful, particularly if the players try to pick up a body and the DM has no idea what weight to assign to that creature. It would also help homebrew creators assign a size to homebrew creatures as long as they know how much the creature weighs (e.g. if basing it off of a real life creature).

[Kane0]

Huh. What would we call that missing category between medium and large?

I'm guessing that category would be the kind of creature that takes up 2x1 5' spaces rather than 2x2?

[PhantomSoul]

The human body surprisingly has a density that is very close to water, which is about 62.4 lbs. per cubic foot. There are 125 cubic feet in a 5 foot cube, or 7800 lbs. if the entire cube is filled with water. Average human weight is around 150 lbs, or roughly 2% of the cube... Is my math right? This would mean that a human body only fills about 2% of the 5 foot cube they occupy, or that you could stack about 50 bodies in that volume.


That does make some sense; the Space you Occupy isn't the space you occupy, to be coy. (It's just the space you "control" in combat -- yes, I know you know this! :) ) In practice, it's therefore likely to be more about reach (and Reach), including weapons where applicable, than about how hefty a creature is. If heft matters, you probably get pushed into dealing with contested checks!

[MaxWilson]

I'm a little bit skeptical about that 2% figure (I expect Large and Huge creatures to take up proportionately more of their actual spaces) but the actual numbers you get for horses seem reasonable.

Spot-check: let's look at giants though. A Frost Giant is more than 3x as tall as a human being. Let's use a muscular, 200 lb. human as a base, and scale that up by a factor of 3.1 cubed. 200 * 3.1^3 is 5958. That's... surprisingly close actually to the figure you got by assuming 2% of the volume is occupied by the monster. Huh. I mean, it's off by 50% but it's not off by an order of magnitude or anything.

Spot-check #2 (non-humanoid): Mammoths. (I would use T-Rex but the 5E T-Rex is absurdly small compared to a real T-Rex--it can squeeze its entire body into a 10' x 10' cube!.) A 5E Mammoth is Huge, 15' x 15', which seems reasonable for a creature that was up to 13' high at the shoulder and 8.8 tons. Here we run into more serious discrepancies. The 2% formula predicts that a Mammoth ought to weigh only 4212 lb. but according to Wikipedia it would weigh up to 17,600 lb, which is about 4x more.

Tentative conclusion: the formula is okay for humanoids but needs to be adjusted based on body plan. Quadrupeds should have a 2x to 4x multiplier. Perhaps 2x for relatively lean creatures like tigers and dogs, 3x or 4x for squat creatures like rhinos and mammoths.


I also noticed that there's an odd jump from medium to large, where large is twice as big as medium, whereas all other size increases (including from tiny to small, and small to medium) are by a factor of 1.41 (the square root of 2, or two steps is double the size). Because of this, each step in size should increase the weight by about 2.83 times, or by 8 times for every two steps.

Aren't Small and Medium both the same size, 5' x 5'?

[Greywander]

Huh. What would we call that missing category between medium and large?

I'm guessing that category would be the kind of creature that takes up 2x1 5' spaces rather than 2x2?
I'm working on a doc that extends the size system up and down a few sizes, and adds in this missing size. I'm currently calling it "big", for lack of a better name. Light horses and goliath would probably be big, draft horses would probably be large. Big creatures take up a 10 foot square (like small creatures take up a 5 foot square), but you can stack them 2x2 in a 15 foot square. I'm also allowing small creatures to stack 3x3 in a 10 foot square.


That does make some sense; the Space you Occupy isn't the space you occupy, to be coy. (It's just the space you "control" in combat -- yes, I know you know this! :) ) In practice, it's therefore likely to be more about reach (and Reach), including weapons where applicable, than about how hefty a creature is. If heft matters, you probably get pushed into dealing with contested checks!
True, I did know this! I was just surprised at how little of the space they actually took up. But 50 bodies in a 5 foot cube sounds realistic. And you're probably right about reach. Humans have pretty long arms, so I'd expect us to be comparatively light for our size category compared to something like a wolf that has basically zero reach.


Tentative conclusion: the formula is okay for humanoids but needs to be adjusted based on body plan. Quadrupeds should have a 2x to 4x multiplier. Perhaps 2x for relatively lean creatures like tigers and dogs, 3x or 4x for squat creatures like rhinos and mammoths.
As noted by PhantomSoul, I think reach is the key. A human has a much longer reach (proportional to their size) than a mammoth does. If the mammoth had human-like arms, it would probably be a gargantuan creature. It would probably be sufficient to add a simple weight trait to different creature that deviate significantly from the average weight, multiplying the average weight by 2 or 3 or 4, or maybe 2/3 or 1/2. It still wouldn't be fully accurate, but it could give a much closer estimate. Most of the time it would only matter if you needed to pick up one, but having even a rough estimate can help a DM who suddenly finds they need that number because their players are doing something dumb and definitely not what they prepared for.

Edit:

Aren't Small and Medium both the same size, 5' x 5'?
Yes and no. Small creatures take up a 3.5 square space, which is rounded up to a 5 foot square. Going one step smaller than 3.5 feet gives the 2.5 feet you'd expect for tiny.

Edit2:
I noticed that this table has listed weight ranges for different size categories, and they don't quite match mine:
https://dungeons.fandom.com/wiki/SRD:Table_of_Creature_Size_and_Scale

[Kane0]

I'm working on a doc that extends the size system up and down a few sizes, and adds in this missing size. I'm currently calling it "big", for lack of a better name. Light horses and goliath would probably be big, draft horses would probably be large. Big creatures take up a 10 foot square (like small creatures take up a 5 foot square), but you can stack them 2x2 in a 15 foot square. I'm also allowing small creatures to stack 3x3 in a 10 foot square.


Perhaps tongue-in-cheek but i’d call it ‘sizable’

[anthon]

Tiny 3 lbs
small 25 lbs
medium 200 lbs
large 1600 lbs
huge 12800 lbs
gargamel 102,400 lbs

[MaxWilson]

Yes and no. Small creatures take up a 3.5 square space, which is rounded up to a 5 foot square.

Is that your own interpolation or have I overlooked something in the PHB?

[Greywander]

Is that your own interpolation or have I overlooked something in the PHB?
Sorry, it was late last night and I should have specified this point. It's my interpretation, but it fits with the math. As far as I'm aware, RAW small creatures are identical in size to medium. Mathematically, small creatures should occupy a roughly 3.5 foot cube, but since you can't fit more than one in a 5 foot square they just round up to occupying a full 5 foot square. You should be able to fit 3x3 small creatures into a 10 foot cube, though (almost, you need to round down a bit).

Ever since 5e came out, the small size has felt like the odd size out, like it was merely a half step between medium and small. Once you look at the math, it actually makes sense that the small size is a full size step, not a half step (though their carrying capacity should be reduced compared to medium creatures). The real strangeness is the apparently missing size category between medium and large. All other size steps are 1.41 times bigger than the previous size, except for large which is twice as big as medium.

[LumenPlacidum]

The human body surprisingly has a density that is very close to water, which is about 62.4 lbs. per cubic foot. There are 125 cubic feet in a 5 foot cube, or 7800 lbs. if the entire cube is filled with water. Average human weight is around 150 lbs, or roughly 2% of the cube... Is my math right? This would mean that a human body only fills about 2% of the 5 foot cube they occupy, or that you could stack about 50 bodies in that volume.

Not that surprising, I think. Much of a human is literally water. I very much doubt that this figure amounts for large body cavities, though. Those cavities make it so that I doubt you could fit fifty humans stacked in a 5 ft cube. You could do it only if you blended them first. That's the figure you're looking at.

The size between Small and Large should be... Powerfully Built, and includes Goliaths and Firbolg.

[MaxWilson]

Sorry, it was late last night and I should have specified this point. It's my interpretation, but it fits with the math. As far as I'm aware, RAW small creatures are identical in size to medium. Mathematically, small creatures should occupy a roughly 3.5 foot cube, but since you can't fit more than one in a 5 foot square they just round up to occupying a full 5 foot square. You should be able to fit 3x3 small creatures into a 10 foot cube, though (almost, you need to round down a bit).

Ever since 5e came out, the small size has felt like the odd size out, like it was merely a half step between medium and small. Once you look at the math, it actually makes sense that the small size is a full size step, not a half step (though their carrying capacity should be reduced compared to medium creatures). The real strangeness is the apparently missing size category between medium and large. All other size steps are 1.41 times bigger than the previous size, except for large which is twice as big as medium.

FWIW I like your reasoning and intend to adopt it. The 5' x 5' Small RAW really, really bugs me.

[Dienekes]

Huh. What would we call that missing category between medium and large?


I think it’s just called Powerful Build.