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

"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 per day 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. But what if you use loose tobacco to roll your own cigarettes or fill a pipe?

The pack-year formula can't be applied to people who smoke using loose tobacco. Instead, a translation can be 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.

Here's the formula to gauge pack-years for loose tobacco smokers, who usually quantify 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

So why is knowing a person's pack-year calculation helpful? Here we take a look at how pack-years could be useful and the debate surrounding the accuracy of how the calculation is used.

Assess Lung Cancer Risk

Pack-years is one measure of lung cancer risk for people who smoke. According to the Centers for Disease Control and Prevention (CDC), a person's pack-years, age, and smoking history are used to determine whether screening for lung cancer is recommended.

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.

Assess Risk of Other Smoking-Related Diseases

In addition to lung cancer, a person's pack-year calculation is one of several factors considered when assessing a person's risk of smoking-related cardiovascular disease and chronic obstructive pulmonary disease (COPD). However, studies have suggested that other factors such as smoking duration or intensity, rather than just pack-years, may be important to consider when it comes to risk for heart disease and COPD.

Other Ways to Assess Risk

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.

While smoking is the top risk factor for lung cancer, there are other things that can contribute as well. For example, according to the American Cancer Society, exposure to radon, asbestos—and other toxic chemicals found in some workplaces, air pollution, and secondhand smoke as well as a family history of lung cancer can all be risk factors. Older age is also a risk factor when it comes to lung cancer.

If you want to calculate your risk for lung cancer, the American Association for Thoracic Surgery (AATS) provides a tool for people ages 55 to 79 that takes several risk factors into account; the calculator can even assess your lung cancer risk if you have never smoked. The National Cancer Institute also has an online tool that assesses risk of lung cancer for adults 50 to 80 years old.