It is impossible to know for sure an exact number.  In general, the more severe an ailment, or the more dramatic your goal, the more sessions will be required.  If you read through the Testimonials you will find some examples.  Most patients notice small changes after as little as 1 session.  However, every patient is unique and it is vital that your expectations are not based on the cases of others, but on you alone.  A therapist will help you determine an approximate number of sessions once they know more about your specific case.