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

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. 

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

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.

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

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 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.