Hair grows approximately one-half inch in a month. This breaks down to about one-half millimeter of hair growth each day, and approximately 6 inches per year. Hair grows faster or slower based on factors such as age, genetics and the state of hormones in the body.
Hair grows in three distinct cycles that follow concurrent phases: anagen, catagen and telogen. These three phases occur simultaneously and display specific characteristics that determine how long the hair is. The anagen phase is the growth phase of the hair, while the catagen phase is the transitional phase when hair growth halts. The telogen phase is the resting phase of the hair.