Some NRT products make their recommendations based on what kind of smoker you are. But there is no formal category in any textbook or a group that defines a light, average, or heavy smoker. In general, a light smoker is someone who smokes less than 10 cigarettes per day. Someone who smokes a pack a day or more is a heavy smoker. An average smoker falls in between.
Sometimes a doctor will use the term pack year to describe how long and how much a person has smoked. A pack year is defined as the number of packs of cigarettes a person has smoked every day multiplied by the number of years he or she has smoked. Since 1 pack is 20 cigarettes, a person who has smoked 20 cigarettes a day for a year is considered to have smoked 1 pack year. Someone who has smoked 30 cigarettes a day (1½ packs) for 3 years has smoked 4.5 pack years (1½ x 3), and so on. This is just another way to figure out how high your risk of smoking-related disease might be.