How to calculate accurately the mass of large creatures?

[Sheilawisz]

I have a problem when I try to decide what would be the body mass of some of my Fantasy creatures, because some of them are larger than humans and, in order to guess a proper weight, I have to compare them with the size of other species like large horses and bears.

The thing that troubles me is that maybe I have miscalculated the body mass of my Aylar species, in particular the males, so I have researched a little about the mass of other imaginary species:

According to wikia sites, the Na'vi creatures from the Avatar movie stand 3 meters tall and weigh 210 kilograms. The Wookiees' average height and mass are given as 2.1 meter and 125 kilograms, while the 1m-tall Ewoks are supposed to weigh 50kg.

In my case, the average female Aylars stand 5'8'' tall and have a body mass of 133 pounds.

The problem is that the males of the Aylar species stand 3.7m tall (around 12'3'') and I have calculated their weight as 720 kilograms, approximately equivalent to 1600 pounds. They are human-like in shape, except that they have a long, wolf-life tail that needs to be taken into consideration.

Is that too heavy for a creature that size?

My belief is that if a creature's size is multiplied by two then the weight should be multiplied by eight... Is that correct? How do you calculate the body mass of your Fantasy creatures??

 

[Feo Takahari]

My belief is that if a creature's size is multiplied by two then the weight should be multiplied by eight...

This is basically correct, although there may be other factors at play. If you just need a general estimate, you can probably get away with this.

 

[ThinkerX]

The problem is that the males of the Aylar species stand 3.7m tall (around 12'3'') and I have calculated their weight as 720 kilograms, approximately equivalent to 1600 pounds. They are human-like in shape, except that they have a long, wolf-life tail that needs to be taken into consideration.

This does sound like the old 'game' (AD&D and Warhammer) calculations. Given the Square cube law, though, the male Aylar would have to have unusually dense and strong bones.

For myself, I set the maximum height for large humaniods at around 9-10 feet, and made them skinny for their size, in accord with actual 'giants'. (They also don't consistently breed true, and many have acromengaly - sp?)

 

[Abbas-Al-Morim]

You could look at BMI calculations and then multiply by x. For instance if the BMI for a 6' man would be 250 lbs (no idea if it is, I don't even use lbs) then you could multiply by 2 for someone/something twice his size. Or wouldn't that work?

 

[Sheilawisz]

@ThinkerX: I believe that the problems suffered by humans that grow beyond seven feet happen not because a human-shaped creature cannot grow that large, but because our species in particular is not designed to reach those sizes.

There exists evidence of a different human species that lived before us, apparently giants that could be ten feet tall and beyond. Maybe they had unusually strong bones as you say... They are talked about in books about mysteries and the supernatural, but we know that they were real because we have found their skeletons and tools.

The Aylar skeleton is not made of bone, but of a very strong type of radioactive crystal. The bones are no problem, but I think that maybe a 3.7m tall Aylar should weigh less than 720kg/1600lb.

@Feo: Thanks for the link, it seems that the square cube law is very good but I am not convinced... Maybe it would be more accurate to multiply by six instead of eight, or seven??

@Abbas: For some time I tried to calculate this using the BMI thing... However, those calculations were designed for humans, and the Aylar males are so out of the human scale that it's better to compare them to large horses and bears.

Maybe 600kg would be more acceptable?

The tail alone is 2.2m long (7'3'') and I guess it weighs around 50kg.

 

[ThinkerX]

There exists evidence of a different human species that lived before us, apparently giants that could be ten feet tall and beyond. Maybe they had unusually strong bones as you say... They are talked about in books about mysteries and the supernatural, but we know that they were real because we have found their skeletons and tools.

Ah...your talking of 'Bigfoot', a near mythological denizen of my part of the world. Best I can recollect, though, they rarely top 8 feet in height.

 

[Feo Takahari]

If you remember the name of what you're talking about, I'd love to hear about it--the largest hominids I know of were eight-footers. (Then again, the tyrannosaur proved that bipedalism is at least possible at far greater sizes.)

 

[Guy]

There are accounts such as newspaper articles from the 19th century about road building crews and such finding giant humanoid skeletons, but to my knowledge the evidence is purely anecdotal. I don't know of any of those skeletons actually on display or being studied. But who knows? Perhaps they're in a crate in the basement of the Smithsonian to New York Museum.

 

[ThinkerX]

If you remember the name of what you're talking about, I'd love to hear about it--the largest hominids I know of were eight-footers. (Then again, the tyrannosaur proved that bipedalism is at least possible at far greater sizes.)

'Homo Gigantus'. If memory serves - and my knowledge is decades out of date - there is some fossil evidence for these creatures, but they apparently didn't make it through the last ice age...unless 'Sasquatch' or 'Bigfoot' are their decendants.

I don't believe any of them topped 7-8 foot tall, though.

 

[Sheilawisz]

You can read a lot about the discoveries of giant human skeletons and tools in a book called The Complete Guide to Mysterious Beings, by John A. Keel. The book also talks a lot about the Sasquatch, the Yeti and many other mysteries that inhabit this curious little planet where we live.

A more accepted type of giant humanoid was the Gigantopithecus, a type of huge (obviously!) primate. It has been estimated that this creature could grow to a height of 3 meters and weigh 540 kilograms, which means that it was about the size of a large brown or polar bear. Some people believe that the Sasquatch are actually the Gigantopithecus, but I have a different theory.

Now, talking about Fantasy creatures: The Mountain Trolls from Harry Potter are described as standing over twelve feet tall and weighing a Ton. I assume that a ton means a thousand kilograms, so that makes them considerably heavier than my Aylar Guardians. The Aylar is more slender than the Troll anyway, so I guess it makes sense.

The crystal bones could be heavier than normal bones... Maybe it's impossible to calculate this accurately and I should simply have an estimate, who knows.

 

[Svrtnsse]

We discussed this in chat, but I'll put it in here for reference, just in case.

The mass of and object is calculated by multiplying it's volume with it's density.
The volume of something can be acquired in a couple of different ways (dip it in a full bucket of water and see how much flows over), but the easiest and least messy way is to multiply it's dimensions (X, Y and Z). For object more complex than basic geometrical shapes this is a nuisance so in a case like this it's probably easier to just guess a volume or something.

Now for some examples:

The volume of our object is X*Y*Z and we want to know what the volume of an object twice as big is. By twice as big I mean it's dimensions are doubled. Like this: 2X*2Y*2Z. This can also be written as 2*X*2*Y*2*Z, which in turn is the same as 8*X*Y*Z.
We still don't know what the actual volume is, but we know that it's 8 times larger than of the original object. Assuming the density of both objects are the same we get that the object is also 8 times heavier.

...which is basically what Sheilawisz said from the start.

Id argue that for fictional purposes it's a good enough approximation but that you should add a little bit extra to compensate for larger creatures probably being more heavily built.

 

[wordwalker]

Also, more low-magic worlds can do plenty with an "ogre" that's only eight or so feet tall-- give it a heavy build or a quick temper and that's big enough to make it nearly invincible in the simpler fights against humans. (For one thing, think of the reach it's got!) At least if it's also smart, decently armored, or hasn't yet run into smart opponents that know how to get around its killer swing.

 

[psychotick]

Hi,

If they're humanoid then use the cube rule. Simply take the average height of a man, say five foot ten, divide it into the height of your critter e.g. eight foot, and get a ratio - roughly 1.37. Then cube to get 2.5 more or less, and multiply by the average weight of a man, say 80 kg. So 200kg more or less. After that through in your fudge factor, big bones, slender build etc. (Sorry for mixing units by the way.)

Cheers, Greg.

 

[Nobby]

I don't think giving your creations crystal bones would be an advantage, crystals, although they can repair themselves (technically ) tend to be more of the spikey yet brittle persuasion. All living creatures use their bones not just as a support system but also as anchor points for musculature and engines for tissue maintenance. If the crystals you are talking about are the glassy kind, how exactly could mushy biology bind itself to them?

I also can't imagine the kind of biology that would require their own skeletal system to be uniquely antipathetic to cell replication (erm radioactive).

Still, there may well have been Giants in those days...

I don't mean to be sarcastic, I just wanted to prod you a bit

 

[Sheilawisz]

Thank you, Svrtnsse.

You have convinced me that the Cube Law is the best way to calculate something like this. After considering it for some more time, I have come to the conclusion that 1600lb is a good weight for the 12'3'' tall Aylar Guardians. I was afraid that it would be too much, but they can weigh that and still be quite slender creatures.

@Wordwalker: I do not really like Ogres. The Aylar Guardians are actually very gentle creatures that are totally devoted to the protection and admiration of the smaller females of their species, but yeah... When they get mad, they can cause a hell of a destruction with their powers, their claws and their horrible strength =)

@Greg: I tried that, and it gave me a result of 340 kilograms instead of 720. That would be way too slender, so 720 is better and more accurate after all.

@Nobby: I know that my Aylars sound very unrealistic, but that's part of my style. Their crystal bones can be broken, but it takes a huge amount of strength and pressure to do that. Their bodies have evolved to resist and take advantage of their own radiation (which gives them special powers), but this radiation is lethal to almost all the other species in their worlds.

I have not explained how the tissues can attach themselves to a crystal skeleton, that's a good point to think about...