Calculating your pack years is straightforward once you know the Pack Years formula and what each input means. This guide explains the method in plain language, walks through a manual calculation, and gives worked examples you can follow — then you can do it instantly with the Pack Years Calculator.
What is Pack Years?
The Pack Years calculation tells you your pack years from a few simple inputs. The figure you are solving for here is the pack years.
The Pack Years formula
The core formula is:
Pack years = Cigarettes per day ÷ 20 × Years smokedHere is what each input means:
- Cigarettes per day — a number. Example: 20.
- Years smoked — a number. Example: 10.
How to calculate it step by step
- Write down the cigarettes per day (for example, 20).
- Write down the years smoked (for example, 10).
- Apply the formula above to get your pack years.
- Double-check the result with the Pack Years Calculator.
Worked examples
Example 1
| Input / Output | Value |
|---|---|
| Cigarettes per day | 20 |
| Years smoked | 10 |
| Pack years | 10.00 |
With cigarettes per day of 20 and years smoked of 10, the pack years works out to 10.00.
Example 2
With cigarettes per day of 40 and years smoked of 10, the pack years works out to 20.00.
| Result | Value |
|---|---|
| Pack years | 20.00 |
Example 3
With cigarettes per day of 10 and years smoked of 10, the pack years works out to 5.00.
| Result | Value |
|---|---|
| Pack years | 5.00 |
Tips for an accurate result
- Keep your units consistent — mixing, say, months with years or grams with kilograms is the most common source of error.
- Round only at the very end. Rounding inputs early can shift the final answer noticeably.
- Re-run the numbers whenever an input changes, rather than estimating from an old result.
- These figures are general estimates, not medical advice — check with a qualified professional before acting on them.
Prefer not to do the maths by hand? — the Pack Years Calculator does it instantly, for free, with the formula and a worked example built in.
Related calculators
Continue exploring health calculators with these tools: BMI Calculator, Corrected Calcium Calculator, Anion Gap Calculator, QTc Calculator (Bazett), Maintenance Fluid Calculator (4-2-1 Rule).