A full man bun uses all the hair on your head and requires more hair than the other styles. If you don’t have 9–16 inches (23–41 cm) of hair, choose a different style. A full man bun is the best kind of bun to wear for formal occasions. The crown of your head is where the back and top of your head meet. Most buns will be in between the crown of your head and the center of the back of your head. Run your fingers through your hair and bunch all of your hair to the area where you want the man bun to be. This will include all the hair on the back and sides of your head as well.  Don’t pull your hair back too tightly or it may be uncomfortable. If you don't want a messy bun, run a comb through your hair before you style it. Doing this will give your bun an even more refined look, but isn’t always required. Leave out a couple of strands of hair when you tie the bun initially and wrap those strands around the bun and hair tie. Secure the extra piece of hair by pulling it through the tightened hair tie. If your hair is too short or straight to stay wrapped around the bun and hair tie, you could use a firm hold hair spray or a pomade to lock your hair in place.

Summary:
Grow your hair out to at least 9–16 inches (23–41 cm). Pull your hair back and bunch it up towards the crown of your head. Wrap a couple strands of hair around the elastic band to hide it.