I can't find a 100% reliable source (it may have been stated in an episode of the show and I missed it) but a few places online list Doof's height as 6'2''. Dwayne Johnson's about 6'4'', relatively close, and has a shoe size of 14, or a little over 12''. I was able to fashion the Rock's shoes into a makeshift ruler, comparing both him and Doof (had to use an image of him unslouched, of course) to the ruler itself, and adjusting it until 1 shoe = 12 inches exactly. I then measured Doof's feet to be approximately 14 inches from heel to toe, and thus a US size 20.

I love doofinshmirds haha do u know his shoe size?