Definition of Pack-Years of Smoking

How to Calculate How Many Pack Years You Smoked

Senior woman smoking
What does the term pack years mean?. PhotoAlto/Eric Audras/Brand X Pictures/Getty Images

Definition: Pack-Years

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 women appear to develop lung cancer after fewer pack-years of smoking than do men.

Examples of Calculating Pack-Years:

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.

Lung Cancer Screening 

Recently, doctors have studied the number of pack-years of smoking to determine who should be screened for lung cancer. Studies suggest that people who have a 30 pack-year history of smoking, are between the ages of 55 and 80, and continue to smoke or have quit in the past 15 years, are candidates for CT lung cancer screening. Studies using these criteria have found that the mortality rate from lung cancer could be cut by 20 percent if people meeting these criteria undergo screening.

Pack-Years and Smoking Risk

In general, the more pack-years you have smoked, the greater the chance of getting cancer.  That said, lung cancer occurs in never-smokers, and many people chain smoke for decades without getting cancer. Though people aren't statistics, you might be wondering about the likelihood that you will develop lung cancer.

Check out this article:  What Percentage of Smokers Get Lung Cancer?

Pack-Years and Heart Disease Risk

The number of pack-years someone has smoked is correlated not only with lung cancer, but with heart disease, lung diseases such as COPD, and others.

Pack Years and Disease Calculator

Formulas are now available in which pack-years are used to estimate the risk of developing conditions such as lung cancer and COPD. On a population level ,these calculators can give us good information about risk, but there are several limitations when looking at the value for individual people. There are a multitude of risk factors for lung cancer, or against lung cancer, which are not considered in these calculations, and the risk of an individual may be much greater or much less than would be predicted using this measurement alone.


While the number of pack-years a person has smoked is a useful tool in determining risk, it is not foolproof. There is some controversy that the duration of smoking may be an important factor to consider, especially in determining lung cancer risk. The age of onset of smoking may play an important role as well, for example, two people with the same calculated risk based on pack-years, the one who began smoking at an earlier age may be at greater risk.

A Word From Verywell

Since you are looking for the definition of pack-years, you may feel concerned about your own or a friends smoking history. We are here to let you know that even if you smoked in the past there are still things you can do to improve your wellness. If you smoked in the past, make sure to review the criteria for lung cancer screening. If you smoke, it's never too late to quit and we have some awesome resources to get you started. And there are always things you can do to lower your lung cancer risk. For ideas on reducing your risk - and in a way that is fun rather than another list of things to avoid - check out these superfoods that may reduce lung cancer risk based on solid scientific research.


Blackmon, S., and S. Feinglass. The United States Preventive Services Task Force recommendations for lung cancer screening. Thoracic Surgery Clinics. 2015. 25(2):199-203.

Fucito, L., Czabafy, S., Hendricks, P. et al. Pairing smoking-cessation services with lung cancer screening: A clinical guideline from the Association for the Treatment of Tobacco Use and Dependence and the Society for Research on Nicotine and Tobacco. Cancer. 2016. 122(8):1150-9.

Guaraldi, G. et al. Lung and Heart Diseases Are Better Predicted by Pack-Years than by Smoking Status or Duration of Smoking Cessation in HIV Patients. PLoS One. 2015. 10(12):e0143700.

Janjigian, Y. et al. Pack-years of cigarette smoking as a prognostic factor in patients with stage IIIB/IV non-small cell lung cancer Cancer. 2010. 116(3):670-5.

Peto, J. That the effects of smoking should be measured in pack-years: misconceptions 4. British Journal of Cancer. 2012. 107(3):406-407.

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