The average rate of hair growth is about 0.5 inches (1.25 centimeters) per month, which translates to about 6 inches (15 centimeters) per year. However, the rate of hair growth can vary depending on factors such as genetics, age, gender, nutrition, and overall health.
Hair growth is a continuous process that occurs in three phases: anagen, catagen, and telogen. During the anagen phase, which lasts for 2-7 years, the hair actively grows. During the catagen phase, which lasts for 2-3 weeks, the hair follicle shrinks and detaches from the blood supply, and the hair stops growing. During the telogen phase, which lasts for 3-4 months, the hair is in a resting phase and eventually falls out, allowing new hair to grow.
It's important to note that hair growth is not always uniform across the scalp, and hair growth rates can also be affected by factors such as medications, stress, and hormonal changes.