Definition and examples
Pack years are defined as follows:
- Number of pack-years = (number of packs smoked per day) x (years smoked).
So, if 1 pack was smoked per day for 4 years, the number of pack-years = 4. A pack usually contains 20 cigarettes. If the number of cigarettes per day is known, the value can be calculated as follows:
- Number of pack-years = (number of cigarettes per day / 20) x (years smoked).
