The average gorilla is 5 feet tall (60 inches) and has an erect penis length of 1.25 inches. In the new Godzilla vs Kong movie, Kong is around 400 feet tall. Assuming Kong's closest relative is the gorilla, we can first divide 1.25 by 60 and multiply by 100 to get an average penis to body ratio of 2 percent. Assuming this crosses over to Kong's species we can find 2 percent of 400 feet to get 8 feet. Kong's penis is 8 feet long when full mast.