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Definition of Pack-Years


Updated July 14, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Senior woman smoking
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Pack-years is a measure of how much someone has smoked. Since lung cancer is directly related to the number of cigarettes smoked, using pack-years can help physicians identify which people are most at risk of developing lung cancer.

One pack-year of smoking would mean that someone had smoked one package of cigarettes (20 cigarettes) daily for one year.

Researchers look at pack-years when assessing the role of smoking in causing various diseases, and also to compare different groups of people. For example, some studies suggest that women are more susceptible to the carcinogens in cigarettes, because they appear to develop lung cancer after fewer pack-years of smoking than do men.

In the future, physicians may look at pack-years of smoking to determine who should be screened for lung cancer.


Jill smoked 1 pack of cigarettes daily for 20 years. She has a 20 pack-year history of smoking.

Frank smoked 2 packs of cigarettes daily for 20 years. He has a 40 pack-year history of smoking.

Eleanor smoked 10 cigarettes (1/2 pack) per day for 20 years. She has a 10 pack-year history of smoking.

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