The average growth rate for human hair is up to a half inch every 28 days. This is equivalent to a yearly maximum hair growth of 6 inches.
The hair growth cycle has several different stages: anagen, catagen, telogen and exogen. The anagen stage is the hair growth phase in which hair grows about a third of an inch per month. The hair on a person's scalp is in this active growth phase for 2 to 6 years. However, hair on other body parts, such as the arms, legs and eyebrows have a shorter growth phase.
While the catagen phase is a transitional stage that can last about 2 weeks of the hair growth cycle, telogen is a resting phase that lasts nearly 4 months. The last stage is the exogen or shedding phase in which a person can shed up to 100 hairs each day.