Board Thread:Questions and Answers/@comment-37587452-20181202221521/@comment-27950421-20181202231827

Yeah, my estimates for the lamia puts the average lamia at around a ton. Due to the organs that are present in the human torso instead of the length of the serpent body, the volume is replaced with either fat or muscle mass. Most images of lamia show them having a fairly lean and muscular tail, it's likely muscle and it's dense muscle at that, which increases the weight considerably. I'd put the average lamia at around a ton, particularly large individuals reaching a ton and a half.

Centaurs likely weigh 20 to 30 lbs more than a horse of comparable size (a human torso is a bit bigger than a horses head.)

Harpies likely have a 7 to 15 ft wingspan depending on the closest comparable bird, though a 10 to 13 ft wingspan is likely the average. Harpies living in denser forests having smaller wings to make it easier to navigate between trees and Harpies living in wide open planes and deserts having larger wings to make it easier to glide and catch up drafts.

Krackens... the tentacles in every image I've seen of then simply aren't big enough to sink a ship. Either them sinking ships is an example of rumor and hearsay affecting the contents of the encyclopedia (it is written from the point of view of an in-universe character known as the wandering scholar so much of the information in the encyclopedia isn't completely accurate) or the Krackens have the ability to either shift into a "primal form" like dragons or extend their tentacles to enormous lengths and shorten them back down. Either way that would make their exact size and weight highly variable. As they are, I'd put them at something like 350 to 400 lb.