an open door

let's start with horse math, because it's a lot more straightforward.

again, the guesstimate for safe rider weight is 15-20% of a horse's body weight.

this is the industry trick i learned when assigning horses to guests at dude ranches, but sources corroborate.

so, how do we apply that? well, if you, like me and stephenie mormon, are from the bad ol' us of a, when you think "horse" you probably think something like this:

there are SO MANY horse breeds, and if i get into it we will in fact be here forever. just know, the ones you're looking at up there are kind of your "typical" riding horse. a lot of riding breeds are going to have similar sizes and weights--about 800-1200 lbs (360-544 kg), giving us an average safe rider weight of 160-240 lbs (72-108 kg).

as you can probably guess, this...isn't great for vampires.

but! your quarter horses, saddlebreds, thoroughbreds, morgans, etc (and fine i'll specify arabians too) are NOT the only type of horse out there. see, those breeds were all cultivated over the years for specific types of riding, like racing long distances or terrorizing cows.

but draft horses?

draft horses were bred specifically to handle weight. they were medieval english war horses carrying knights in full armor, and then they worked on farms, pulling plows. they are large, and they have MUSCLE. you can tell this by looking at them, especially when compared to other horses. [sources here, here & here]

if vampires are selective breeding to make horses for themselves, they're doing it with these guys. (probably belgian drafts, percherons, and, of course, the shire horse, which all the heaviest known horses have been.) these are in an average weight range of 1600-2400 lbs (725-1090 kg) [source]. assuming our vampire horse breeder, my new favorite oc, is good at their job, they consistently get the higher end of that. it is, after all, an average--the heaviest recorded horses were both over 3000 lbs (1360 kg) [source & source]

15-20% of the average weight of drafts is how we get our estimate of 360-480 lbs (163-218 kg) vampire carrying capacity.

with the understanding that that's actually probably on the lower end of what the vampire horse program could achieve! also, just for funsies, if our vampire has succeeded in consistently breeding 3000 lbs (1360 kg) horses, our riders can be 450-600 lbs (204-272 kg).

some more miscellaneous thoughts:

yes, draft horses were originally bred/used for pulling plows and weights, but they're still super rideable! people today typically aren't riding shire horses, but that's just because it's a rare breed really only found in the uk. i've ridden plenty of belgian drafts, and there's a whole thing happening right now with people training percherons to jump. which looks cool as fuck.

in some ways, drafts might even be ideal for vampire horse cultivation! obviously individual horses have personalities and breed isn't a guarantee, but drafts do tend to be a lot calmer and less easily spooked than say, an arabian or a thoroughbred. (can you tell i have beef with one specific horse who happened to be an arabian)

however, our beloved vampire horse cultivator is probably going to run into issues with the fact that draft horses do have some unique health issues, a lot of which are genetically inherited, and others that happen specifically because they are so much larger. they will tend to have shorter lifespans (closer to 20 than 30). breed carefully!

now it's time for a hefty disclaimer.

because the thing is, that 15-20%? it is not a hard-and-fast rule. i'm making a silly fandom post and that's the easiest way to do the math, so i'm using it, but in reality, what is "safe" for a horse is a complex question that you can really only answer individually! weight is not the only thing that matters.

for one obvious example, a horse in better shape and well-muscled is a safer bet than a horse that's out of shape and overweight, even if that second horse is heavier! also, the age of the horse matters a lot. (this is part of why every racehorse on the tracks is like. three.) the shape of their back, their height, their hoof condition--all of this is super important!

even stepping beyond the horse for a second, the saddle you're using matters, because saddles add way more weight than you think! a "cowboy" roping saddle can weigh up to 50 lbs, which is 50lbs less that you want the rider to be, whereas an english saddle is more in the realm of 15. the activity you're doing is important too! the harder the horse is exerting themself, the lighter you want the rider. this is why jockeys are tiny, and every madwoman who does the lord's work of rehabbing off-the-track thoroughbreds is not.

and, most relevant for our purposes, the skill of the rider matters. a lot.

the better you are at riding, the more you can balance in the saddle, distribute your weight off the horse's back, and move with their momentum so they're doing less work. if you know how to sit a trot (the horse's least comfortable speed), then you won't be bouncing your weight awkwardly into their back, so it doesn't matter as much what that weight is. and so on!

this is also why a horse's carrying weight for packs is much lower than people--all those dried beans are not consciously adjusting their weight to make things easier.

as we all know, stephmeyer vampires are impossibly fast, strong, could stroke a soap bubble without popping it, etc. they've probably got horse balance down. you'll see some vampire weights over these "limits" later, but i think they'd probably be okay.

i also say all of this because the "horse world" has a massive problem with fatphobia, and i care a LOT about the fact that it's toxic bullshit. yes, rider weight matters for the horse's safety, but the vast majority of people weaponize that unfairly to be bullies. i'm not about to talk about horse weights and not acknowledge that.

alright! i think that's everything i can let myself say about horses, or we'll be here even longer. know that i could though. someone come ask me about horse lacrosse.

so. how much do vampires in twilight weigh?

here it is. the real million-dollar question. the reason i had to make a spreadsheet and ctrl-f my way through a whole lot of twilight content.

because here's the thing.

we get exactly one (1) canon source on vampires being heavier or denser than humans.

in Midnight Sun's take on the meadow scene, edward thinks: "...it would take quite a bit of effort for her [Bella] to heft even just my hand without my help. I was a little heavier than I looked." (Midnight Sun, Chp. 17, "Confessions")

there's some other canon you can interpret in line with this, such as bella not being able to move edward out of the sun in new moon--though i and i think a lot of other fans originally just interpreted this as "he's strong"--and the sections in the official illustrated guide (my beloathed) where meyer says things like:

"the cellular membrane of the vampire is not as soft or permeable as in a human cell; it has crystalline properties" (pg. 48)

"the stonelike firmness of the vampire body creates a look similar to muscle, making any size human appear more fit as a vampire" (pg. 48)

"Their skin is harder than granite, rendering their bodies nearly indestructible" (pg. 51)

and of course, my most hated details:

"Vampires do not have a circulatory system. Their bodies are harder than human bodies, but their cells are selectively porous." (pg 51)

"Internally, the vampire's system contains many venom-based fluids that resemble, and in some cases perform the same function as, the human fluids that were replaced...this venom works as a lubricant between the hard cells of the skin, making movement possible." (pg 49)

now. i've lost my goddamn mind about twilight vampire biology (and the existential horror of consciousness!) before, so i won't do it here. for our purposes (horse propaganda), i want to draw just a few important conclusions.

vampires are inarguably heavier than humans of the same size would be. their "cells" are "harder" (STEPHENIEEEEEE), their body has a "stonelike firmness," and edward says he's heavier than he looks.

vampires are not, however, just giant rocks. i will make some weight estimates based on the average density of solid rocks/minerals, BUT those are likely higher than the real weight of these vampires, because vampires are, like humans, largely liquid inside! the liquid is just...venom. um. (do vampires have bones?!?! hey--do vampires--) moving on. liquids are less dense than solids--you know this, that's what makes something a liquid, the molecules are more spread out--so a vampire will actually weigh much less than a rock the exact same size and shape as that vampire. yay.

for any of this to work, we just have to assume edward doesn't know what the fuck he's talking about. he's a little heavier than he looks, fine--but for bella to struggle to LIFT HIS HAND from HER LAP TO HER FACE? the average human hand weighs slightly less than a pound. obviously there's also the weight of his arm, the element of surprise, etc, but--she has to be able to lift his hand, or else nothing makes sense and we must accept that vampire venom is like. fucking. liquid osmium or some shit. which would just break the goddamn universe, because then how much energy would they have to expend to fucking move, and how are they getting that energy from drinking ~5 liters of blood every two weeks or so--

edward is underestimating bella's strength because he chronically underestimates humans. MOVING ON.

with all of that in mind, let's get into tumblr's favorite: the actual motherfucking math.

disclaimers: "density" here refers to volumetric mass density. i do a LOT of rounding up. bmi is in the background like a terrible ghost, because i had to estimate the body volumes of some fictional vampires, and the equations that exist to do that are all based on bmis. i know it's racist psuedoscience, i'm sorry. i will NOT get technical about weight vs. mass, i dropped my physics degree all those years ago for a reason.

before we get into vampires, i'd like you to have some information about humans as a reference.

the average human body's average density is 1 g/cm^3 [source; source], and the average weight of a human in the US is 185.5 lbs (84 kg), according to the CDC as of 2023.

i've simplified egregiously, obviously. body density is way more complicated than that. it's affected by things like how much air is in your lungs! this is literally just here as a reference point. also in the spirit of not stressing myself out, i've given up and been us-centric with that weight estimate. because hey, there's naturally a fuck-ton of variation in human bodies, and the one source i could find for worldwide data was a) from 2005 and b) so varied that an average from that was functionally useless and i gave up digging for a median. i'm sorry.

now. vampire time. let's high-ball and say they are just rocks, density-wise.

i've arbitrarily picked three rocks to use as a point of reference here, based on physical descriptions of twilight vampires: quartz, with an average density of 2.625 g/cm^3; marble, 2.78 g/cm^3; and diamond, 3.515 g/cm^3. [source] averaging those three together gives us a platonic ideal vampire rock density of 2.973 g/cm^3.

the way that we apply density to figure out vampire weight can be summarized simply. density tells us how much an object weighs per amount of space it's taking up, so all we need to do is figure out how much space the vampires are taking up, their volume, and multiply that by the density. (i TOLD you i'm not talking about weight vs mass)

this is where the spreadsheet comes in. because, while we don't know the vampires' canon weights, we do know all of their heights, thanks to my archnemesis the illustrated guide. for example, jasper whitlock (who you people all think is a cowboy) is 6'3" (190.5 cm), while maría (to pick a totally random female vampire NOT just because i'm obsessed with her) is 5'1" (155 cm).

once you know someone's height, you can estimate a body volume, based on the human body's "typical" proportions and the weight you assume it would be. i used two steps, and two online calculators to accomplish this:

this weight calculator, which uses a few different popular formulas to find "ideal body weight" based on height and gender. again, yes, there's rampant bias here, but i am oversimplifying a LOT and working with what resources are easily available. i selected the Hamwi formula results, & highest end of bmi 'ideal body weights' when hamwi was unavailable. it's still almost certainly underestimating--emmett, for example, is 211 lbs with this formula, but i know in my heart that man is built like a wwe hall-of-famer and would be 320 human lbs at LEAST.

this body volume calculator, which uses height and that calculated weight to estimate body volume. this gave me an output in liters.

to go back to our examples, we now know that jasper would have a body volume of about 85.97 L, and maría about 59.67 L. i...did this for every individual vampire whose height is listed in the illustrated guide, and yes. i made a spreadsheet.

great news though, we're now at our last step. multiply this volume by whatever density you want, and you know how much a vampire would weigh! and because the metric system is so kind, the g/cm^3 ratios i gave above are the same as kg/L, no conversion needed! so we literally just have to multiply. (which, if you have made a spreadsheet, is very easy to have a computer do for you.)

to go back one last time to our brave examples:

at the density of quartz, jasper is 498 lbs (226 kg) and maría is 345 lbs (157 kg)

at the density of marble, jasper is 523 lbs (239 kg) and maría is 366 lbs (166 kg)

at the density of diamond, jasper is 666 lol lbs (302 kg) and maría is 462 lbs (210 kg)

it was many words ago that i was talking about horses, so a refresher: i estimated a safe low-end rider weight of 360-480 lbs (163-218 kg), but potentially getting as high as 450-600 lbs (204-272 kg).

this means that at the density of quartz, most of steph mayonnaise's vampires would probably be okay.

a lot of the male vampires (especially, emmett and felix) would be pushing it unless they were getting The Biggest Possible horses--because smeyer constructed a universe where 90% of men are over six foot and women are lucky if they make it past 5'5"--with an average weight of 455 lbs (206 kg) and a median of 471 lbs (213 kg), which i specify because there's some real outliers in this data set (alec. it's alec, the literal child. the romanians are also short kings). the women are generally fine--siobhan and the amazonian coven start pushing it at 490-540 lbs (222-245 kg), but on average twiight female vampires are 391 lbs (178 kg), median 380 lbs (173 kg). (the outliers are on the other side for the female vampires! horrifyingly, jane is really not that much smaller than alice, who's not that much smaller than charlotte, who's--you get the picture.)

averaging the men and women's average weights together is how i got that 423 lbs (192 kg) above, and my assertion that they'd probably be okay.

now, obviously, if vampires are more comparable to marble or diamond, we start to run into trouble. but, most non-metallic rocks and minerals are in that lower quartz-like range, (2.5-2.6 g/cm^3), so i think it's honestly safer to guess that. i mostly threw marble and diamond in there because i thought it was funny.

also, vampires are almost certainly less dense than a solid chunk of rock in their shape would be!

we know that vampires have a lot of liquid venom in them. we aren't sure how much, but the human body is roughly 60% water. let's assume a similar ratio for vampires and venom.

if we very conservatively guessed that venom has the density of the molten version of whatever rock they are, quartz when molten has a density of 2.55 g/cm^3 [source; source], which may not seem like a huge difference from 2.625 g/cm^3, but scales up fast! our sacrificial quartz jasper would be just 489 lbs (222 kg) and maría 340 lbs (154 kg). for jasper, even that ten-pound difference is significant for horse carriability.

also! i frankly think it's really unlikely that the venom has the density of molten rock. it must be something completely structurally different, given that suburbia meyer claims it's facilitating movement, and that it's extremely flammable when vampire skin isn't. to headcanon-ize my own half-baked understanding of biology, venom is likely converted from blood somehow, which in humans has an average density of 1.06 g/cm^3. so the venom's probably similar!

(i did fail to hunt down an estimate of the density of snake venom to compare. but. snake venom is 80-90% water and then a whole bunch of proteins and enzymes--which is basically what blood is! don't talk to me.)

being as uncharitable as possible to these poor vampires that just want to ride some horses, let's round up to a venom density of 1.1 g/cm^3. if that liquid is 60% of a vampire's body composition? they're all beyond fine.

quartz jasper is just 324 lbs (147 kg), and maría 224 lbs (102 kg). marble jasper is 336 lbs (152 kg), and maría 233 lbs (106 kg). even diamond jasper makes it easily, at 392 lbs (178 kg), and maría a measly 272 lbs (123 kg). which still makes them significantly heavier than a human of their same volume would be--195 lbs (86 kg) and 133 lbs (60 kg) respectively.

fuck our draft horse rider weight of 480 lbs (218 kg), some of our smaller vampires with this formula are okay on a plain old quarter horse at 240 lbs (108 kg).

🎉vampire horse is real!!!!!🎉

now, if you made it far enough to read this, i'll be honest: i came into this with ulterior motives. i wrote "i think they can do it" before i did any math or research at all. that said, i hope i've convinced you, because i certainly convinced myself! and i can't tell you how much i appreciate you coming on this journey with me.

...also. just between us. one of the horse photos up there is my old rodeo gal, the love of my life. you can probably guess which. rest easy, joey <3

and never forget.