Calculating Pack-Years (Smoking)

Calculating pack-years is a skill you will be required to use in different fields of physiotherapy, but particularly in respiratory physiotherapy.

Why is it important?

Smoking is the leading cause of preventable morbidity and premature mortality in developed and developing countries. Calculating pack-years can give clinicians a measurable quantification of a patient’s exposure to tobacco use. An individual's tobacco use is highly correlated with the risk of developing lung cancer and heart disease.

How to calculate pack-years:

Pack -ears = The number of years smoked x the average number of packs smoked per day.

1 pack = 20 cigarettes


1) 20 cigarettes per day for 8 years = 8 pack-years

20 cigarettes = 1 pack

20/20 = 1

1 pack x 8 years = 8 pack-years

2) 10 cigarettes per day for 6 years = 3 pack-years

20 cigarettes = 1 pack

20/10 = 0.5

0.5 packs x 6 years = 3 pack-years

Limitations of pack-years:

A key limitation to note when calculating pack-years is the misrepresentation of the number of cigarettes smoked and the severity of the calculated pack-years. For example, 5 cigarettes a day smoked for 20 years is the same as 20 cigarettes smoked for 5 years i.e. 5 pack-years for both. However, the risk of smoking-related pathology is significantly greater in the former example.

Therefore, it is important to note the following to provide some context when documenting a patient's pack-year history:

- Start and Stop dates.

- The number of years the patient has smoked

- The number of pack-years

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