How is cigarette pack-year calculated?

• A. # of packs smoked per day x # of years person has smoked
• B. # of cigarettes smoked per day x # of years smoked
• C. Pack size x years since quitting
• D. (Packs per week) x (years smoked) divided by 7

Answer: (A)

Pack-years measure lifetime smoking exposure by multiplying how many packs a person smokes per day by how many years they have smoked. One pack per day for one year equals 1 pack-year, and the standard pack contains 20 cigarettes, so you can convert cigarettes per day to packs per day by dividing by 20 if needed. For example, smoking 0.5 packs per day for 20 years equals 10 pack-years.

Using cigarettes per day times years would give cigarette-years, not pack-years, which isn’t the standard unit. Using years since quitting focuses on time after cessation, not the total exposure from smoking. The weekly-based option adds unnecessary steps and can cause confusion, since the conventional measure uses daily packs multiplied by years.