Oversized equipment - How much heavier?

[Greywander]

The Square-Cube Law tells us that if we double the size of something, it gets eight times heavier. This is because we're doubling all three dimensions: length, width, and height. If we were to only double one dimension, e.g. the length, while the width and height remains the same, then the weight would only double.

We could then assume that a suit of armor made for someone twice as large as a normal person (a Large creature instead of a Medium creature) should then also weigh eight times as much, but I'm not so sure about that. We're assuming that the larger armor will have four times the surface area, which makes sense since it needs to cover the larger creature, but also that it will have twice the thickness, and I'm not convinced that it would necessarily be any thicker.

On the one hand, we'd expect oversized weapons to have an easier time cutting through armor, and thus oversized armor would need to be thicker to compensate. But this then means that armor should decrease in value against larger weapons. But all armor provides the same AC benefits, regardless of the armor's size or the weapon it is going up against. For that matter, due to the Square-Cube Law, scaling up a weapon would eventually get to the point where the weapon's own weight compromises its structural integrity, so we might even expect oversized weapons to be proportionally narrower and all around just a bit smaller than you'd expect.

This also applies going smaller, but in reverse. If armor got thinner on smaller creatures, then eventually it would provide almost no protection against Medium sized weapons.

Does anyone have any insight on this?

[The Glyphstone]

Those same creatures you need larger armor and weapons for would be dead under the Square Cube Law anyways, wouldn't they? Dead things don't need armor or weapons, unless you're a necromancer...

[Greywander]

That's... not really a helpful answer in any way.

If D&D doesn't operate off of the Square-Cube Law, then how does a change in size affect weight? Presumably, weight still scales at the same rate; if anything it would be more plausible that strength scales up more quickly than in real life such that the Square-Cube Law does not apply. Or it could just be magic. Giants and dragons just have impossibly strong bones and muscles that allow them to handle their prodigious weight. It's just feels harder to make the argument that an object with 8x the material wouldn't also be 8x heavier than it does to somehow reason that scaling a creature up makes them stronger than in real life.

Regardless, however weight and size are related, the question remains of how much heavier a weapon or suit of armor would be for a larger creature.

[JNAProductions]

For 5E, your Carrying Capacity is 15*Strength Score.
I believe each size up doubles your Capacity, so a Huge Storm Giant would have 60*Strength Score Carrying Capacity. That is 60*29, or 1,740 pounds.

Plate Armor weighs 65 pounds for a Medium creature. If it's multiplied by 8 for going up a size category, it'd be X64 for a Huge creature. That is 64*65, or 4,160 pounds.

Pushing, Dragging, or Lifting something is up to double your Carrying Capacity. This drops your speed to 5'. For a Storm Giant, that's 3,480 pounds.

In other words, being realistic within the confines of the game, a Storm Giant can't even move their own Plate Armor, let alone wear it and fight in it.

[Greywander]

Well, except for the step from medium to large, one step up is only √2x bigger, not 2x bigger.

Going from medium to large would be 2x the size, then from large to huge would be about 1.4x, for a total of about 2.8x the size of medium. So it would only be about 22.6x heavier, or about 1470 lbs. This is still unreasonably heavy, but it's within its carrying capacity.

Since going from medium to large only doubles your carrying capacity, when it should actually quadruple it, we could even treat it as not doubling, but only increasing by √2. Thus, huge, being two steps up from medium and therefore "double" the size, would only be 8x the weight, or 520 lbs.

Now, this all assumes that doubling the size of the plate armor will also double its thickness. If it doesn't, then the armor won't increase in weight as quickly as we scale it up. If the thickness remains constant, then the armor would actually increase in weight at the same rate as carrying capacity.

Despite what I said in my last post (partly because I forgot about this), we know that doubling a creature's size in D&D increases their carrying capacity by 4x, which agrees with the Square-Cube Law. Medium to large is an anomaly, as is small to medium, but the relationship can clearly be seen going from large to huge to gargantuan. If you account for the fact that small creatures should actually occupy a 3.5-foot square, and it just rounds up to 5 feet to make it easier to use, then the relationship also applies to going from tiny to small.

TL;DR, aside from some questionable exceptions in the size rules, there is a clearly implied general rule that dictates that the Square-Cube Law holds true in D&D, at least with regards to carrying capacity. Weight, on the other hand, is generally handwaved and not mentioned. This is probably why the grapple rules use their own rules to slow you down while grappling, instead of just going off of how much the grappled creature encumbers you.

[Zhorn]

I've thought about this before.
We could take some equipment sized for larger creatures with known weights and work backwards from there.

SKT p234: Gurt's Greataxe, 325 lb. (sized for Huge)
A regular greataxe is 7 lb.
325/7 = 46.4285714286
two size categories larger than Medium, so the root of that
√46.4285714286 = 6.78232998313
so less than a x8 multiplier there

SKT p234: Rod of the Vonindod, 100 lb. (sized for Huge)
Rods usually weight between 2-5 lb. for Medium creatures (DMG p139), we'll go with 5 lb for this since it is an adamantine object.
100/5 = 25
two size categories larger than medium, so the root of that
√25 = 5
less than a x8 multiplier again

Then there's barding from the PHB (p155), while we know it isn't 'humanoid shaped', it's not specifying there there is relatively more or less armor-to-body-surface-area once accounting for size, so for game simplicity we're just treating this as a 1-to-1. Also since gear is typically weighed as though for Medium creatures, we're assuming the values given for barding are for Large creatures.
According to the text, barding has a x2 weight modifier, far less than x8.

[JNAProductions]

I don't think you're gonna find consistency. D&D isn't realistic-and I highly doubt the designers spent much time on weights to make sure they check out.

Greywander, I'm curious as to what you're hoping to glean from this? Is this just idle curiosity, or is there something specific in mind?

[Zhorn]

I don't think you're gonna find consistency.

That's actually part of what I was getting at. While a spell such as Enlarge would strictly follow the Square-Cube Law and use the x8, equipment that was actually made for larger creatures and not just magically scaled up does not.

So taking a reductionist paraphrasing of Greywander's post we have the question;
"Does equipment weight follow the Square-Cube Law when being sized for creatures other than Medium?"
And we can use the books to get our answer
"No, they weigh less than that"

[Greywander]

Greywander, I'm curious as to what you're hoping to glean from this? Is this just idle curiosity, or is there something specific in mind?

I'm working on a 5e mod, and one of the smaller parts of it is cleaning up and expanding the size system. Part of that is that I want to lay out consistent rules for the price and weight of over- and undersized items. Small characters now use weapons sized for them, instead of just using medium sized weapons (this means that small-sized greatswords and longbows are now available). I'm also adding in the "missing" size between medium and large, and it will probably feature in playable races (centaurs, goliaths, and such), which means that a typical PC could be using any of three sizes of equipment.

Basically, I just want to remove the guesswork by having specific rules to handle this.

As for barding, it specifically calls out that, "The cost is four times the equivalent armor made for humanoids, and it weighs twice as much." So I think it's only referring to medium-sized mounts. Which is kind of strange, but that's what it says.

Edit:

I've thought about this before.
We could take some equipment sized for larger creatures with known weights and work backwards from there.

SKT p234: Gurt's Greataxe, 325 lb. (sized for Huge)
A regular greataxe is 7 lb.
325/7 = 46.4285714286
two size categories larger than Medium, so the root of that
√46.4285714286 = 6.78232998313
so less than a x8 multiplier there

Part of the problem is that large straight up doubles your size over medium, but still acts as a single step up, where it should take two steps to double in size. Since huge is two steps up from medium, treating huge as twice the size means that an item simply scaled up verbatim should weigh 8x as much. Where a medium greataxe weighs 7 lbs., a huge greataxe would then weigh 56 lbs.

But let's say that we count huge as being three steps up, since large does, in fact, double your size over medium. This means the axe should weigh about 22.6 times as much (8x going from medium to large, then another √8x, or about 2.8x, going from large to huge). The huge axe should then weigh about 158 lbs. Even in the worst case scenario, it's still less than half what the huge axe actually weighs. So somehow the axe is even heavier than it should be. Most likely, it was a heavier axe to begin with, not just a normal axe scaled up.

SKT p234: Rod of the Vonindod, 100 lb. (sized for Huge)
Rods usually weight between 2-5 lb. for Medium creatures (DMG p139), we'll go with 5 lb for this since it is an adamantine object.
100/5 = 25
two size categories larger than medium, so the root of that
√25 = 5
less than a x8 multiplier again

5 * 8 = 40 lbs, which is far less than 100 lbs. 5 * 22.6 = 113 lbs., which is actually in the right ballpark. And not every rod is 5 lbs., so it makes sense that it's slightly over. To me, this supports the idea that items (or weapons, at least) scale up according to the Square-Cube Law. But it might be different for armor.

I'm... really not sure I understand where you're getting your numbers from.

Edit 2:
Seeing these numbers, I'm actually leaning toward not imposing a penalty for using oversized weapons, since the weight of those weapons is already enough of a deterrent, and it's a common fantasy trope that someone strong enough can wield an oversized weapon. Though to be fair, I'm also nerfing oversized weapons. A weapon only does +1 damage per size step smaller, e.g. a medium weapon does +1 damage against small creatures. They also do less damage against larger creatures, so an oversized weapon would help with both.

[Kane0]

It's all madness, just pick a rate you're comfortable with and stick to it.

[Zhorn]

I'm... really not sure I understand where you're getting your numbers from.

The ones I list the book sources for?
Or do you mean the formula I'm reversing the calculation for?

The method I'm using is if the Square Cube Law was being adhered to, then the weight of an object sized:

Large = Medium object weight x 8
Huge = Medium object weight x 8 x 8
Gargantuan = Medium object weight x 8 x 8 x 8

As this is how the weight would be increasing under the Enlarge spell (One size category increase = x8 weight multiplier), which has been worded on PHB p237 as adhering to the Square Cube Law.
Now as that x8 is what we are questioning, we treat that as the variable to be solved using the Huge objects of known weight.

Huge = Medium object weight x 8 x 8
A = B x C x C
A = B x C²
A/B = C²
√(A/B) = C

I can see where some confusion is as this just doesn't align with your homebrew definition of how big a size step is

Well, except for the step from medium to large, one step up is only √2x bigger, not 2x bigger.

We don't have a size category between Medium and Large. Medium to Large is a single incremental step, not two, and not √2 or 1.4. PHB p237 Enlarge/Reduce "This growth increases its size by one category—from Medium to Large"
Perfectly fine to insist for your own system you are developing, but it's not a value drawn from the books.
(side note for the record; I don't think we should be using the Square Cube Law for equipment, and I do overall agree with the approach you are taking as a homebrew answer)

As for barding, it specifically calls out that, "The cost is four times the equivalent armor made for humanoids, and it weighs twice as much." So I think it's only referring to medium-sized mounts. Which is kind of strange, but that's what it says.

... and I think you're wrong on this one. "equivalent armor made for humanoids" is because that is the base item being referenced, armor that has been sized and priced for medium humanoids, being the default player character size, but the default mount size is Large. PHB p198 specifies the mount needs to be one size category larger than the rider. Player Characters are be default medium = Mounts are by default Large, and the equipment prices as presented would be for that default.

A human buys barding for both themselves and their horse.
Chainmail for the human (Medium) is 75 gp 55 lb.
Chainmail Barding for the horse (Large) is 300 gp 110 lb.

[Greywander]

The ones I list the book sources for?

I meant the random square roots you were taking, but I think I understand it now.

I can see where some confusion is as this just doesn't align with your homebrew definition of how big a size step is
We don't have a size category between Medium and Large. Medium to Large is a single incremental step, not two, and not √2 or 1.4. PHB p237 Enlarge/Reduce "This growth increases its size by one category—from Medium to Large"
Perfectly fine to insist for your own system you are developing, but it's not a value drawn from the books.
(side note for the record; I don't think we should be using the Square Cube Law for equipment, and I do overall agree with the approach you are taking as a homebrew answer)

I'm not sure you understand. The step from medium to large is an anomaly, an exception. There's no general rule stated, but we can infer a general rule from what's given.

The step from large to huge is an increase from a 10 foot square to a 15 foot square. That is not a doubling in size. It's a √2 increase in size, albeit rounded up slightly. Likewise going from huge to gargantuan. You have to go from large to gargantuan to double in size. The step from medium to large is the odd man out here, being the only time going up a single step doubles your size. I speculate that at one point a size between medium and large might have been proposed, but it was likely dropped because it would have been too big to fit in a 5 foot square, so it would have to round up to a 10 foot square, and it wouldn't have been a meaningful difference from large.

Small is also an anomaly, but I think this one is actually explained by rounding. Going √2 up from tiny or down from medium, what we would expect for a small size is a 3.5 foot square. But again, that's too big to fit more than one in a 5 foot square, so it just rounds up. Also, for some reason there's no change in carry weight between small and medium.

Anyway, if we correct those anomalies, which I'm doing in my own system, then this tracks perfectly with the Square-Cube Law. Each step up is a √2 size increase, and your carry weight doubles. This means that a two step increase doubles your size and gives you 4x carry weight.

... and I think you're wrong on this one. "equivalent armor made for humanoids" is because that is the base item being referenced, armor that has been sized and priced for medium humanoids, being the default player character size, but the default mount size is Large. PHB p198 specifies the mount needs to be one size category larger than the rider. Player Characters are be default medium = Mounts are by default Large, and the equipment prices as presented would be for that default.

A human buys barding for both themselves and their horse.
Chainmail for the human (Medium) is 75 gp 55 lb.
Chainmail Barding for the horse (Large) is 300 gp 110 lb.

I'm not convinced. You can get barding for animal companions, too. Small PCs also exist, so medium sized mounts do as well. You can get barding for your horse, mastiff, and familiar. Now, it's possible that neither price nor weight change depending on size, but that seems unlikely. What seems more plausible to me is that the devs just forgot about it.

It's all madness, just pick a rate you're comfortable with and stick to it.

Yeah, you might be right.

Interestingly, if oversized weapons do extra damage, and larger creatures can carry more, then it would seem like larger PCs would be strictly better, right? (Well, until you have to squeeze through a tight space.) Enforcing the Square-Cube Law might actually be one way to balance it out. Yes, you can carry twice as much, and yes, you do slightly more damage, but you pay for it by having your weapons and armor taking up a larger proportion of your carry weight. And while you could opt to use an undersized weapon, the same option doesn't really exist for armor.

[Hytheter]

I speculate that at one point a size between medium and large might have been proposed, but it was likely dropped because it would have been too big to fit in a 5 foot square, so it would have to round up to a 10 foot square, and it wouldn't have been a meaningful difference from large.

I'd say you're overthinking. They probably just set man-sized things as the default creature size, assigned them a 5ft square, and categorised larger critters based on the number of squares they occupy. I highly doubt √2 size multipliers were a consideration at any step of the design process.

[Greywander]

I'd say you're overthinking. They probably just set man-sized things as the default creature size, assigned them a 5ft square, and categorised larger critters based on the number of squares they occupy. I highly doubt √2 size multipliers were a consideration at any step of the design process.

And yet that's how it ended up. But it's actually quite plausible that they stumbled on that by accident.

Still, √2 size steps make a lot of sense and work pretty well. I've even found a way to change how their space occupied is measured so that it has the exact area that it is supposed to, e.g. it can make a small creature occupy a space that is exactly twice the area of a tiny creature and half the area of a medium creature. You just use diamonds instead of squares. So a small creature occupies a diamond that fits inside a 5-foot square. Technically, it's just a roughly 3.5 foot square rotated, but while 3.5 is an approximation, the diamond is actually the exact right size. You can then pack small creatures closer together, as the diamond shapes leave empty spaces between squares. E.g. a 10x10 area can fit five small creatures, as there's a gap in the middle for the fifth one. The diamond also works for the size between medium and large, but once you get up to huge it might be easier to just use the 15-foot square instead of a 20-foot diamond. Circular tokens are probably the best option, though.

[Hytheter]

And yet that's how it ended up. But it's actually quite plausible that they stumbled on that by accident.

It only works in the sense that any '1, 2, 3, 4' sequence kinda works in multiples of √2 if you add a whole new '1.4' step to the sequence where it didn't previously exist. Which is to say, not really. When I go the store I can buy eggs in cartons of 6, 12, or 18; that doesn't suggest the existence of a missing 8-9 egg carton, it suggests that the sequence is simply linear rather than multiplicative.

Still, √2 size steps make a lot of sense and work pretty well. I've even found a way to change how their space occupied is measured so that it has the exact area that it is supposed to, e.g. it can make a small creature occupy a space that is exactly twice the area of a tiny creature and half the area of a medium creature. You just use diamonds instead of squares. So a small creature occupies a diamond that fits inside a 5-foot square. Technically, it's just a roughly 3.5 foot square rotated, but while 3.5 is an approximation, the diamond is actually the exact right size. You can then pack small creatures closer together, as the diamond shapes leave empty spaces between squares. E.g. a 10x10 area can fit five small creatures, as there's a gap in the middle for the fifth one. The diamond also works for the size between medium and large, but once you get up to huge it might be easier to just use the 15-foot square instead of a 20-foot diamond. Circular tokens are probably the best option, though.

The thing is that most normal humans don't want to perform calculations based on multiplying square roots or divide a perfectly good square grid into diamonds for niche edge cases like trying to squeeze a bunch of halflings into a small area. Making a game mathematically exact doesn't make it fun.

[Greywander]

It only works in the sense that any '1, 2, 3, 4' sequence kinda works in multiples of √2 if you add a whole new '1.4' step to the sequence where it didn't previously exist. Which is to say, not really. When I go the store I can buy eggs in cartons of 6, 12, or 18; that doesn't suggest the existence of a missing 8-9 egg carton, it suggests that the sequence is simply linear rather than multiplicative.

If it were linear, then tiny creatures (and small creatures, for that matter) would occupy a 0 foot space. It's going in increments of 5 feet, right?

Though it's not implausible to use one scale going up, and a different scale going down.

Take a look at this size chart from an older edition. You'll notice that some additional sizes that were removed in 5e, likely to help streamline the game. If it were linear, then the next step up from gargantuan would be a 25 foot square, but it's not; colossal is a 30 foot square. This fits the √2 size steps. Seems like for going down, though, they just start halving the size, but also round it. So yeah, I'd believe there wasn't really any rhyme or reason to it, and they just picked sizes that sounded good.

The thing is that most normal humans don't want to perform calculations based on multiplying square roots or divide a perfectly good square grid into diamonds for niche edge cases like trying to squeeze a bunch of halflings into a small area. Making a game mathematically exact doesn't make it fun.

This is why I like the use of diamonds: it's a perfect geometric representation that doesn't require any hard math. It's really not hard to understand that if you have a 2x2 formation of halflings, that you can fit a fifth one in the middle between the four. Otherwise, they mostly behave like medium creatures, which is how the vanilla rules handle them anyway.

[Hytheter]

If it were linear, then tiny creatures (and small creatures, for that matter) would occupy a 0 foot space. It's going in increments of 5 feet, right?

Though it's not implausible to use one scale going up, and a different scale going down.

Well yeah, like I said they started with Medium as the default one-space because man-sized units are the typical PCs and common enemies as well. Obviously that'd necessitate a different scale for smaller units because you can't have something less than one space large. If you want less than a carton, you probably have to buy the eggs individually.

Take a look at this size chart from an older edition. You'll notice that some additional sizes that were removed in 5e, likely to help streamline the game. If it were linear, then the next step up from gargantuan would be a 25 foot square, but it's not; colossal is a 30 foot square. This fits the √2 size steps. Seems like for going down, though, they just start halving the size, but also round it. So yeah, I'd believe there wasn't really any rhyme or reason to it, and they just picked sizes that sounded good.

...Huh, the lack of a 25ft category is strange and does lend credence to your theory for upward size progression. I'm still inclined to think it was largely based on gut feeling, though. Maybe they just wanted the biggest size category to feel extra special.

[Zaile]

Not sure if anyone mentioned this, but square-cubed assumes all dimensions.

Plate armor for a large creature can be just as thick as plate mail for a medium one, just covers twice the body area. So it wouldn't be x8, more like x2 to x4. Same scale up to Huge.

I agree it's silly that somehow a giant wouldn't be strong enough to wear armor sized for it.

I think because of the surface area and for simplicity sake, just double the weight at each size category for equipment. \

https://en.wikipedia.org/wiki/Square%E2%80%93cube_law

[CapnWildefyr]

Pick a number, like +25%/size category, or whatever, and run with it.

The thing is, a fire-giant-sized sword won't be made the same way as a "human-sized" sword. Neither will the armor. Plate barding, if you recall, also is not like plate mail -- you don't cover a horse's legs for example, you mostly put some plates and protection on the front and sides (more or less). And, when making swords, the metal bends too much if you just hammer it flat. So a fire-giant smith won't make a flat sword, it will have runnels and ridges and slots or whatever to stiffen the blade and reduce the weight.

Sticking with fire giants, even their armor might not cover the same areas that human armor does. It depends on what the giants feel are the most likely vulnerable areas. While they are humanoid, the size difference and combat techniques might make them use less armor in some areas, depending on who they think they will be fighting -- other giants, dwarves, etc. All of this just adds weight points to making a simple rule and going with it, without getting overly technical and worrying about a volumetric expansion, because the expansion won't be volumetric.

For other objects, like bows, size might be more of a drawback than weight. Hard to draw a bow when your armspan is 3 feet too short. A fire giant bow might be, what, 15 feet tall, with a 3-4 ft draw back length? Better off using the arrow like a knife on a stick, or turning the bow into a "ballista."

[animewatcha]

Googled a bit. Search term of "The Square-Cube Law" without quotations Thanks for linked a 'quickie linkie' for the Square cube law.
Looks like it doesn't appear to adhere strictly to 2 - 8 exactly though there are formula for how the increase in size would affect other things. Also apparently, one of the 'google questions' that it tries to guess what you are asking 'Does the square-cube law apply to humans?' The answer 'when simplified' is a no and going more in indepth in a scienceworld link that I don't know if I can link here.

If it can't 'properly' be applied to a human in reallife, it may become harder to apply to humanoid and non-humanoid races in a fantasy game.

[EnnPeeCee]

I haven't gone through all the math here; but it seems like everyone is using the assumption that the size category combat space dimensions are equivalent to the creature's dimensions.
Per PHB:

A creature's space is the area in feet that it effectively controls in combat, not an expression of its physical dimensions.

Lets look at an example, Human (Medium) vs Ogre (Large). The space rules say this is a step from 5'x5' to 10'x10'. But looking at their descriptions:

An individual can stand from 5 feet to a little over 6 feet tall and weigh from 125 to 250 pounds.

The average adult specimen stands between 9 and 10 feet tall and weighs close to a thousand pounds.

The actual increase in height is somewhere between 1.5x to 2x, depending on which ends of the spectrum you look at.

Or to throw the numbers off more, how about Goliath:

Goliaths are between 7 and 8 feet tall and weigh between 280 and 340 pounds. Your size is Medium.

That's only a 1.1x to 1.4x difference between a medium and large creature.


Point being, I think you are using apples to calculate oranges. Combat space is a game abstraction, grouped into categories for game balance. Combat space and actual creature dimensions may be roughly related, but using one to calculate the other is never going to have consistent or meaningful results.

[JLandan]

According to the sidebar on pg 204 of the PH, there is no physics in D&D. There is just background magic and functional magic. Everything emanates from that. Since magic can be anything under any conditions, no physical laws exist. So... the weight increase does not have to correspond to size increase in any way. Which means its DM's call.

[Sigreid]

I meant the random square roots you were taking, but I think I understand it now.


I'm not sure you understand. The step from medium to large is an anomaly, an exception. There's no general rule stated, but we can infer a general rule from what's given.

The step from large to huge is an increase from a 10 foot square to a 15 foot square. That is not a doubling in size. It's a √2 increase in size, albeit rounded up slightly. Likewise going from huge to gargantuan. You have to go from large to gargantuan to double in size. The step from medium to large is the odd man out here, being the only time going up a single step doubles your size. I speculate that at one point a size between medium and large might have been proposed, but it was likely dropped because it would have been too big to fit in a 5 foot square, so it would have to round up to a 10 foot square, and it wouldn't have been a meaningful difference from large.

Small is also an anomaly, but I think this one is actually explained by rounding. Going √2 up from tiny or down from medium, what we would expect for a small size is a 3.5 foot square. But again, that's too big to fit more than one in a 5 foot square, so it just rounds up. Also, for some reason there's no change in carry weight between small and medium.

Anyway, if we correct those anomalies, which I'm doing in my own system, then this tracks perfectly with the Square-Cube Law. Each step up is a √2 size increase, and your carry weight doubles. This means that a two step increase doubles your size and gives you 4x carry weight.


I'm not convinced. You can get barding for animal companions, too. Small PCs also exist, so medium sized mounts do as well. You can get barding for your horse, mastiff, and familiar. Now, it's possible that neither price nor weight change depending on size, but that seems unlikely. What seems more plausible to me is that the devs just forgot about it.


Yeah, you might be right.

Interestingly, if oversized weapons do extra damage, and larger creatures can carry more, then it would seem like larger PCs would be strictly better, right? (Well, until you have to squeeze through a tight space.) Enforcing the Square-Cube Law might actually be one way to balance it out. Yes, you can carry twice as much, and yes, you do slightly more damage, but you pay for it by having your weapons and armor taking up a larger proportion of your carry weight. And while you could opt to use an undersized weapon, the same option doesn't really exist for armor.

Large weapons don't necessarily need to use twice the material. When it comes to thickness of weapons and armor, there'd be a point where the job is done and additional thickness would provide negligible benefit or maybe even a hinderance to performing the intended job.