Should I consider hair extensions or allow my hair grow out to the desired length I want? Human hair grows approximately 1/2 inch per month on average. This implies that if you want to have very long hair you have to wait more than 5 years. Or rather than waiting that length of time you can just receive hair extensions. Always make sure that you consult with a professional before purchasing or using any kind of hair extensions or hair products that may result in damage to either your natural hair or scalp.