Is it normal for hair to grow 9 inches a year?

Last June, a year from now I cut nearly all my hair off so I was left with half an inch and now my hair is at my shoulders even when I cut about an inch and a half off my hair which means my hair is about 8 inches long! I think my hair has always been like this cos whenever I used to wash it, it always seemed to grow and I have regrowth from dying my hair in February and it is just over 8cm long, an average growth rate of 4/5 of an inch a month! How can this be when hair is supposed to grow only 6 inches a year?