So I came on intending to ask how much meat there is on a 20 foot long giant python. And more generally, what's a good guideline, given my players seem determined to butcher anything that doesn't speak and a few things that do. But in the process of typing up the post I got the answer.
First... Reticulated pythons commonly measure up to 21 feet in length and 165 pounds, although the record setter was a 25 foot, 550 pound monster. Looking at dressed weight yields for real animals gets me a loss of up to 50%, so call it 80 pounds of meat, perhaps higher for a real monster with max hit points.
But I still wanted that general guideline, and HD seemed like a nice rule of thumb.
I observed once that the weights for animals on the livestock table seem to map to the dressed weights for modern animals, which is a nice touch. Goats are 1 HD and 125 lbs dressed weight, cows are 3 HD and 550 lbs dressed, so that's a start. Doubling weight for every additional hit dice works going from 1 to 3 HD, but then it breaks down higher up around elephants. You need to put the brakes on somewhere or it gets ridiculous.
Elephants are 9 HD and weigh 1000 stone. I don't know if that's intended to be dressed weight, but if it's 10,000 pounds and wikipedia says elephants weigh 15,000 pounds it looks like it could be. On the other hand, how likely are you to get 100% efficiency in butchering an elephant? And I find a reference to an occasion when Paris, under siege, raided it's zoo for the butchers, and a young elephant, expected to yield 3000 pounds of meat, produced only 2000. Inconclusive.
But clearly different kinds of animals will have different weights, even for the same HD, and at this point I remembered I hadn't dug into my L&E preview. I thought no, no one would drill down that far, but just to check I opened the pdf and found chapter 4, and after scrolling up and down a little bit, there was Alex, lying in a hammock, sipping a fancy mixed drink with an umbrella in it and asking me what took so long.
A monster’s weight is determined by its HD and its body mass exponent, according to the formula weight = (HD x 10)BME.
Well, of course, what could be simpler? A serpentine body form has a BME ranging from .9 to 1.31, giant pythons have 5 HD, and plugging 501.31 into a calculator gets me... 168 and some decimals, close enough to the normal weight of a real world 20' python to put some faith in the game numbers. I hardly even know what to say, except there it is.
Now I just need to do the math on some of the more likely candidates for my encounter charts and write them in my core book and I'll be prepared next time they delay going into the dungeon to butcher random monsters.