How big is a skeleton?

[Kerrick]

I'm trying to figure out how much cubic footage a skeleton of various sizes would occupy. The reason for this is that I'm making an epic spell that creates a Gargantuan construct called a bone juggernaut, and I need to know how big it is. Also, one of the creature's abilities is that it can absorb bones, repairing 1 hp of damage per cubic foot. I'm figuring a Small skeleton is around 3 cu. ft., a Medium 8, a Large 17, a Huge 30, and a Gargantuan 50, but I wanted to get a second opinion - it seems like I'm way underestimating the higher I go.

 

[CRGreathouse]

How do you want to measure the volume? Just the volume of the bomnes themselves, or also of the now-empty cavities?

 

[Celebrim]

Bones take up larger percentages of body volume as size increases, and volume is a cubic function. I suspect you'll find the results surprising on the low end rather than the high.

Tiny: .015 - .03 ft.^ per skeleton
Small: .075 - .2 ft.^3 per skeleton
Medium: .25 - .5 ft.^3 per skeleton
Large: 1.33 - 2.75 ft.^3 per skeleton
Huge: 8 - 15.75 ft.^3 per skeleton
Gargantuan: 24 - 41 ft.^3 per skeleton
Colossol: 119 ft.^3 per skeleton - 197 ft.^3 per skeleton

Obviously, there are some big gaps there because the size chart tends not to increase that uniformly (page 131 PH for example). The collossol numbers really go off the charts. The bone mass of an great red wyrm dragon is something in the neighborhood of 1826 ft.^3. Also, I maybe underestimating the size of the gaps because they are unsightly to me. An alternative table for the big ones is:

Huge: 9 - 60 ft.^3
Gargantuan: 60 - 300 ft.^3
Colossol: 300 - 2000+ ft.^3

Which only goes to show how broad the range of sizes the big size classes actually cover. I think that the first numbers might be more workable, whereas the latter ones might be more realistic.

You might want to make the mechanic work of HD for simplicities sake.

 

[Brother MacLaren]

What's a human skeleton, about 10 lbs? If bone is about as dense as water, then that would be about 1/6 of a cubic foot. Ballpark figure, close to Celebrim's low-end. Bone is actually denser than water (taking up less space) but not much more so.

 

[cmanos]

how about instead of gaining HP per cubic foot absorbed, you set an arbitrary number per size bracket...

Colossal 64
Gargantuan 32
Huge 16
Large 8
Medium 4
Small 2
Tiny 1
Diminutive 0.5
Fine 0.25

 

[Raging Epistaxis]

About 10 lbs?

I think that is quite conservative... Given that bone is largely mineral, it should be quite heavy per unit volume.

Are we talking totally dessicated or dripping blood? Water weight would affect it some.

My guess would be more like 20-30 lbs for a person my size (6'), but I've never worked with any actual human skeletons that didn't have flesh.

R E

 

[Lonely Tylenol]

I think that is quite conservative... Given that bone is largely mineral, it should be quite heavy per unit volume.

It's largely mineral, but it's also largely hollow and spongy in the centre to make room for all that marrow, which goes away if the bone's dead for a while. Bones are designed to be as lightweight as possible given the structural needs of the organism, which is why larger organisms have denser bones.

 

[Kerrick]

Celebrim - cool, thanks. I'd like to strike a balance between workable and realistic, so I'll probably take the first numbers and tweak them a little.

Cmanos: While hp/size bracket would work, the creature also has the ability to absorb loose bones to repair damage; hence, I need the "hp/cubic foot" thing also.

 

[werk]

I work for GE medical systems in their bone mineral density group, so I thought I'd chime in.

We are generally working with women, so my info only applies to human females (caucasian).

An average 125# person has ~6# of bone mass.

This is only the bone mass, not water or lean tissue like marrow or periosteum or anything 'soft'.

Bone mineral density is largely determined by resistance, that is, strong people have stronger and therefore heavier bones than weaker or hypokinetic people...that is...a large person that is very active would have much more bone mass than an equally large person that is fairly inactive.

As you grow older, your bone size increases while the mass remains the same or decreases, so you have an exponential decline in density, and therefore, bone strength. I am not talking about your bones getting bigger, like at puberty from growth, but rather the continual restructuring that goes on throughout life.

I don't know how this would apply to magical beasts or fantasy creatures. Seems like it would be very hard to come up with a standard equation that works across-the-board.

 

[Celebrim]

I work for GE medical systems in their bone mineral density group, so I thought I'd chime in.

Cool. Nice to have the expert on board. I found information on bone mass pretty easily, but finding information on bone volume proved to be alot harder. For instance, I could fine out how much bones weighed, but not thier density. I ended up finding an estimate of bone volume at 11% of body volume, and a found an estimate of body volume for average humans at somewhere around 80 liters. From there I could work up cubic feet of bone material using the assumption the total volume increased with the cube of the length of the creature and a linear factor necessary to account for the realistic fact that relative bone cross sectional area increases as body mass increases (even though usually D&D ignores this issue, as large D&D monsters tend to have the same body shape as thier smaller counterparts). I don't know how good my numbers actually are.

If you have estimates for dry bone mass, do you have estimates for dry bone density?