A top knot hairstyle is a semi man bun. The hair is kept between 6 to 8 inches long (not any longer) while the hair on the sides and back of the head are kept buzzed with a hair clipper in different types of buzz cuts.f you’d like to tie all of your hair (sides and back included) instead of just tying the hair on the top of your head, then you will need at least 10 inches of hair length. Such a type of man bun is what I call a “full” man bun.