Pack-Years Calculator
Calculate your smoking pack-years — the standard measure of lifetime tobacco exposure.
How to use this tool
- Enter cigarettes per day and years smoked in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your pack-years and the full breakdown beneath it.
Pack-years = (cigarettes per day ÷ 20) × years smoked. It is the standard clinical measure of lifetime tobacco exposure, used to assess lung cancer and COPD risk.
⚠ This tool is for general information and education only and is not medical advice. Consult a qualified healthcare professional before making health decisions.
Formula
Pack-years = (Cigarettes per day ÷ 20) × Years smoked
One pack = 20 cigarettes, so dividing by 20 converts daily cigarettes into packs.
How it works
Pack-years quantify cumulative tobacco exposure by normalising daily consumption to standard 20-cigarette packs and multiplying by the number of years smoked. The metric is the standard clinical measure used to stratify lung-cancer screening eligibility and assess smoking-related disease risk.
The calculation assumes a constant daily consumption rate throughout the smoking history. Variable periods of heavier or lighter smoking can be summed separately as distinct intervals for a more accurate lifetime total.
Worked example
- Input: 20 cigarettes per day, 10 years smoked.
- Convert to packs per day: 20 ÷ 20 = 1.0 pack/day.
- Multiply by years: 1.0 × 10 = 10.0 pack-years.
Pack-years: 10.0
Common mistakes to avoid
- Entering the number of packs instead of cigarettes per day — 1.5 packs/day should be entered as 30 cigarettes, not 1.5.
- Omitting periods of lighter smoking and counting only peak smoking years, which underestimates cumulative exposure.
- Treating pack-years as a standalone risk score with a sharp cutoff; clinicians use it alongside age, imaging, and other factors.
Key terms
- Pack-year
- A unit representing the equivalent of smoking one pack (20 cigarettes) per day for one year; used to measure lifetime tobacco exposure.
- Lung-cancer screening threshold
- Major guidelines (e.g., USPSTF) recommend annual low-dose CT screening for adults aged 50–80 with a 20 pack-year or greater smoking history.
- COPD (Chronic Obstructive Pulmonary Disease)
- A progressive lung disease strongly associated with cumulative tobacco exposure; risk correlates with pack-year total.
- Smoking cessation
- Quitting tobacco; even after many pack-years, cessation reduces ongoing risk for cardiovascular disease, lung cancer, and other conditions.
Frequently asked questions
- What is a pack-year?
- One pack-year equals smoking one pack (20 cigarettes) every day for one year. Smoking half a pack for 20 years also equals 10 pack-years.
- Why do pack-years matter?
- Guidelines recommend annual low-dose CT lung cancer screening for adults aged 50–80 with 20+ pack-years of smoking history. Pack-years are also used to gauge COPD and cardiovascular disease risk.