It's tough to say. Peoples hair grow at different rates. Personally, my hair grows insanely fast, but my best friend's hair grows extremely slow. On average though, it's about half an inch a month, being 6 inches a year.
People has different types of rates in growing hair. Some people grow their hair quite fast some grows their hair very slow. But If you are looking for natural hair growth/regrowth you can also try Reloxe.com.