What Is a Pack Year and How Does It Relate to Me?

Pack Years are a Measure of Lifetime Exposure to Tobacco Toxins

Cigarettes in a pack
Knaupe/E+/Getty Images

As of Dec. 20, 2019, the new legal age limit is 21 years old for purchasing cigarettes, cigars, or any other tobacco products in the U.S.

A pack-year is a term used to describe the approximate number of cigarettes a person has smoked over time.

One pack-year equals 20 manufactured cigarettes smoked per day for one year. 

Examples of Pack Years

Here are a few examples of how pack-years are determined. For the purposes of the calculation, one pack contains 20 cigarettes.

John smoked 10 cigarettes per day for 10 years. 

1/2 pack (10 cigarettes) per day x 10 years = 5 pack-years

Jane smoked 30 cigarettes per day for 26 years.

1 pack (20 cigarettes) per day x 26 years = 26 pack-years

Plus 10 cigarettes (1/2 pack) per day x 26 years = 13 pack-years

26 pack years + 13 pack years = 39 pack-years

Chris smoked 40 cigarettes for 42 years.

2 packs (40 cigarettes) x 42 years = 84 pack-years

What About Loose Tobacco?

The pack-year calculation uses standard manufactured cigarettes, so what if you use loose tobacco to roll your own cigarettes or fill a pipe?

The pack-year formula can't be applied to smokers using loose tobacco. Instead, a translation was derived by measuring the weight of tobacco in traditional cigarettes and relating it to loose tobacco.

Even though there are some differences between the cigarettes you roll yourself with loose tobacco and manufactured cigarettes you buy in a pack, the American Cancer Society reminds consumers that there are health consequences to any type of cigarette you smoke.

Approximately 1/2 ounce of loose tobacco equals 20 commercial cigarettes. 

Here's the formula to gauge pack-years for loose tobacco smokers, who usually speak of how much they smoke in terms of ounces per week.

Ounces per week × 2/7 × number of years smoked = pack years

Why Pack Years Matter

Pack-years is one measure of lung cancer risk for smokers. According to the Centers for Disease Control and Prevention (CDC) pack-years, age, and smoking history are used to determine whether an individual is eligible to be screened for lung cancer.

However, there is some debate about the accuracy and usefulness of using pack-years as a risk assessment for lung cancer.

For example, you might assume that a person who has smoked half a pack of cigarettes every day for 40 years (20 pack-years) is at greater risk for lung cancer than someone who has been smoking two packs a day for 10 years (also 20 pack-years). 

The assertion assumes that less smoking-related health damage occurs within the first 10 years a person smokes compared to the level of damage sustained after 40 years. However, research has shown that even occasional smoking has health consequences.

While it's not a perfect measure of risk, many researchers and clinicians feel that pack-years provide an important perspective on lifetime risk for smokers.

Pack-years are a reasonable measure of the overall exposure smokers and former smokers have had to the toxins in cigarettes in their lifetime, but it isn't the only predictor of smoking-related disease.

In addition to lung cancer, pack-years are one of several factors considered when assessing a person's risk of smoking-related cardiovascular disease and COPD.

If you want to calculate your risk for lung cancer, the American Association for Thoracic Surgery provides a tool that takes several risk factors into account; the calculator can even assess your lung cancer risk if you have never smoked.

Smoking Cessation Help

Smoking cessation is a scary thought for many smokers, but it's never too late to quit. Start by learning about developing strong quit muscles, the supplies to have on hand when you quit, and nicotine withdrawal.

Was this page helpful?
Article Sources
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Cancer Institute (NCI). Definition of pack year. NCI Dictionary of Cancer Terms. Updated February 2011.

  2. Wood DM, Mould MG, Ong SB, Baker EH. "Pack year" smoking histories: what about patients who use loose tobacco?. Tob Control. 2005;14(2):141-2. doi:10.1136/tc.2004.009977

  3. The American Cancer Society medical and editorial content team. Is Any Type of Smoking Safe?. The American Cancer Society. Updated November 2019.

  4. Janjigian YY, McDonnell K, Kris MG, et al. Pack-years of cigarette smoking as a prognostic factor in patients with stage IIIB/IV nonsmall cell lung cancerCancer. 2010;116(3):670–675. doi:10.1002/cncr.24813

  5. Centers for Disease Control and Prevention (CDC). Who Should Be Screened for Lung Cancer?. CDC Division of Cancer Prevention and Control. Updated September 2018.

  6. Peto J. That the effects of smoking should be measured in pack-years: misconceptions 4Br J Cancer. 2012;107(3):406–407. doi:10.1038/bjc.2012.97

  7. Schane RE, Ling PM, Glantz SA. Health effects of light and intermittent smoking: a reviewCirculation. 2010;121(13):1518–1522. doi:10.1161/CIRCULATIONAHA.109.904235

  8. Lubin, J., Caporaso, N. Misunderstandings in the misconception on the use of pack-years in analysis of smokingBr J Cancer 108, 1218–1220 (2013). doi:10.1038/bjc.2013.76

  9. Jaklitsch MT, Jacobson FL. Lung Cancer Risk Assessment Tool. American Association for Thoracic Surgery (AATS).

Additional Reading