Hair doesn't actually stop growing at a specific length. Instead, it stops growing at the end of its hair growth cycle. Each hair follicle goes through a cycle of growth, rest, and shedding. The length of the growth phase (anagen), which is determined by genetics, can last anywhere between two and six years. Once the anagen phase ends, the hair stops growing and either breaks off or sheds.
For instance, if your hair growth cycle is four years, your hair will continue growing for four years, no matter how long it is. After that, it will enter the resting phase (telogen) and eventually shed. This process repeats for each individual hair follicle.
Therefore, while it may seem like your hair has stopped growing, it's actually just reaching the end of its growth cycle.
