I saw sometime a long time back and if I remember correctly, it said the rate of hair growth is between a quarter of an inch a month or up to three quarters of an inch a month. It appears you are clocking in at around half and inch a month.
My hair is about three quarters of an inch a month and maybe a bit more but even at that, I have been growing it out for a short haircut starting around the time I joined Susan's about three months ago and I still have another couple of months before I have the length I need. I learned a valuable lesion and that is don't let my mother and my cutter get together when changing your style. It takes months to grown it back out. 🙁