It depends on a lot of things but mainly the chemicals in your body, the hair type and the texture. Hair growth is largely determined by androgens, the main one being testosterone. Testosterone levels increase during the summer months (for both men and women) so many will notice that during this time their hair grows quicker or thicker.
Individual hairs alternate periods of growth and dormancy (as you have mentioned). During the growth portion of the cycle, hair follicles are long and bulbous, and the hair advances outward at about a third of a millimetre per day. After 3-6 months, body hair growth stops (the pubic and armpit areas having the longest growth period). The follicle shrinks and the root of the hair grows rigid. Following a period of dormancy, another growth cycle starts, and eventually a new hair pushes the old one out of the follicle from beneath. Head hair, by comparison, grows for a long duration and to a great length before being shed. The rate of growth is approximately 1.5cm per month and it doesn�t stop, just alternates between growth spurts and dormancy and eventually just falling out whilst new follicles puch through.
Remember though, hair is a filamentous outgrowth of dead cells from skin � so look after it!!