hair growth rate

The average rate of growth for full-size hairs (called "terminal hairs" by scientists) is about 6 inches (12 cm) per year. (Not everyone`s hair grows half an inch a month, it`s just an average found by those who have studied about hair growth. In fact, some people`s hair will stop growing once it reaches a certain point.)
All hairs grow at roughly the same rate. The length of the growth stage of a follicle can be measured by the length of the hair it produces. For example, a hair 2 feet (48cm) in length would be about four years old at one end, and only a month or so old near the scalp. Contrary to popular belief, cutting your hair will not increase hair growth. All it will do is get rid of the broken and split ends that can weigh your hair down. Broken and split ends are created by excessive heat, such as; curling irons, blow dryers, etc... Hair is damaged also by brushing hair when wet because the dampness makes the hair follicles weaker then usual. The climate around you can also have an affect on your hair. The sun can burn and damage it. The humidity can cause fly aways, however these factors will not slow or quicken the growth rate of your hair. There really is very little that can make your hair grow faster. (In the case of a poor diet, vitamins will help with hair growth.) However, by getting regular haircuts (trims), and staying away from extensive use of products that could fry your hair, such as curling irons, blow dryers etc... you can have healthy, manageable, and beautiful hair.

It just stops growing. I have a client who said she hadn`t had a "real" haircut in four years, and it was only shoulder length. That seems to be the maximum length she can achieve. Everyone has a terminal stage where the hair stops growing. Considering that most hair grows (on average) 6 inches a year, her hair should have been (approximately) 24 inches long. That is about mid-back length. As of right now, she has to be satisfied with shoulder length hair. ;)