Searching for a lore Accurate Size of Mumakil

[Inziladun]

Originally Posted by R.R.J Tolkien

Mumakil Big as a House?


This came from a hobbit nursery rhyme and was not to be taken as literal as Tolkien said in letters 64. Tolkien also never saw himself as writing and his books need to be understood from the perspective of the character and their observations such as a hobbit seeing a massive elephant.

Then again, Sam Gamgee laid eyes personally on the mumakil:

Big as a house, much bigger than a house, it looked to him, a grey-clad moving hill. Fear and wonder, maybe, enlarged him in the hobbit's eyes, but the Mûmak of Harad was indeed a beast of vast bulk.

TTT Of Herbs and Stewed Rabbit

So Sam's standard of size comparison is qualified; still, the beast did have an actual tower on its back, as well as a "giant" warrior (7 feet tall, maybe?), clinging to its neck and looking very small.

With that, I don't think a shoulder height of 20 feet is out of the question.