Pack-Year (Smoking History) Calculator
A pack-year is the clinical standard for cumulative smoking exposure: smoking one 20-cigarette pack per day for one year equals 1 pack-year. Enter cigarettes per day and years smoked to see your pack-years, equivalent packs/day and lung-cancer screening eligibility.
Enter 0–200 cigarettes/day and 0–80 years.
Cumulative pack-years
20.0 PY
Moderate
Risk band
< 10 Light
10–20 Moderate
20–40 Heavy
≥ 40
20–40 pack-years is a moderate exposure and meets one criterion for low-dose CT lung-cancer screening.
Lung-cancer screening reference
Meets the USPSTF 2021 pack-year threshold (≥ 20 PY). If you are 50–80 years old and currently smoke or quit within the last 15 years, discuss annual low-dose CT screening with a clinician.
For reference only — not a clinical assessment. Risk also depends on age, time since quitting and other exposures.
Formula
pack-years = (cigarettes per day ÷ 20) × years smoked
- · Definition source: U.S. National Cancer Institute (NCI Dictionary of Cancer Terms, "pack year").
- · < 10 pack-years: minimal; 10–20: light; 20–40: moderate; ≥ 40: heavy. Bands reflect commonly used clinical strata, not a single fixed guideline.
- · USPSTF 2021 recommends annual low-dose CT (LDCT) lung-cancer screening for adults 50–80 with ≥ 20 pack-years who currently smoke or quit within 15 years (Grade B).
- · In Hong Kong, the Department of Health Smoking Cessation Hotline is 1833 183 (2023). DH/CHP data shows smoking is the leading modifiable risk factor for chronic disease and cancer.
- · If you have quit and restarted, sum your actual smoking years.
- · Doubling cigarettes per day and doubling years contribute equally — 40 cigs × 10 yrs and 20 cigs × 20 yrs both equal 20 pack-years.
Frequently asked
Does smoking even one cigarette a day count toward pack-years?
Yes — proportionally. One cigarette per day is 1/20 of a pack, so a year of that is 0.05 pack-years. The number is small but any smoking still raises cardiovascular and cancer risk.
I have quit smoking — does pack-years still matter?
Yes. Pack-years measure exposure already accumulated and do not reset on quitting. The USPSTF 2021 LDCT screening recommendation covers adults 50–80 with ≥ 20 pack-years who quit within the last 15 years; risk falls over time but stays above never-smokers.
How do e-cigarettes or heated tobacco fit in?
Pack-years were designed for combustible cigarettes; there is no agreed equivalent for e-cigarettes or heated-tobacco products. USPSTF, ACS and other guidelines still base screening on combustible-cigarette pack-years. If you use multiple products, describe usage patterns to a clinician for individual risk assessment.
Where can I get smoking-cessation support in Hong Kong?
The Department of Health Smoking Cessation Hotline (1833 183) offers free phone counselling. Public hospitals, MCHCs, staff clinics and NGOs such as COSH also provide cessation services. Pharmacies sell registered nicotine-replacement therapy (NRT) products.
Related tools
BMI (Body Mass Index) Calculator
Enter height and weight to get your BMI and category (underweight / normal / overweight / obese).
BMR & TDEE Calculator
Estimate daily BMR and TDEE using Mifflin-St Jeor or Harris-Benedict, with calorie targets for cutting and bulking.
Body Fat Calculator (US Navy method)
Estimate body fat percentage using the US Navy circumference formula (neck, waist, plus hip for women).
Sleep Cycle Calculator
Suggest ideal bedtimes or wake times based on 90-minute sleep cycles, so you wake up between cycles instead of mid-deep-sleep.
Daily Water Intake Calculator
Estimate daily water intake from body weight, exercise duration and climate so you stay hydrated without overdoing it.
Running Pace Calculator
Compute pace per km / per mile from distance and time, or project finish time from a target pace — covers 5K, 10K, half- and full-marathon distances.
Heart Rate Zone Calculator
Compute 5 training heart rate zones from age and optional resting HR using the Karvonen formula (Z1 warm-up to Z5 max effort).
Lean Body Mass (LBM) Calculator
Estimate lean body mass (LBM), fat mass and body fat % from height, weight and sex using the Boer, Hume and James formulas.
Daily Macros Calculator (carbs / protein / fat)
Split a daily calorie target into grams of carbs, protein and fat at any macro ratio.
One-Rep Max (1RM) Calculator
Estimate one-rep max from a sub-maximal lift (weight × reps) with Epley, Brzycki, Lombardi and Lander formulas, plus a 50–95% intensity training table.
Body Surface Area (BSA) Calculator
Estimate body surface area from height and weight using the Mosteller, Du Bois, Haycock and Boyd formulas — commonly used in drug-dosing, chemotherapy and cardiac-index calculations.
Race Time Predictor (Riegel Formula)
Project a finish time at one distance from a known time at another distance using the classic Riegel formula T₂ = T₁ × (D₂/D₁)^1.06.
Mean Arterial Pressure (MAP) Calculator
Compute mean arterial pressure from systolic and diastolic blood pressure with clinical bands and pulse-pressure context: MAP = DBP + (SBP − DBP)/3.
Waist-to-Hip Ratio (WHR) Calculator
Divide waist by hip circumference and check the WHO risk bands — a quick screen for central obesity and cardiovascular risk.
Exercise Calorie Burn (MET) Calculator
Use METs, body weight and duration to estimate calories burned for common activities (running, hiking, swimming, cycling and more).
Caffeine Half-Life Calculator
Pick the dose (mg) and the time you drank it; the calculator uses the standard ~5-hour caffeine half-life to project how many milligrams remain hour-by-hour, including the level at bedtime.
Body Adiposity Index (BAI) Calculator
Bergman’s BAI estimates body-fat percentage from hip circumference and height alone (BAI = hip ÷ height^1.5 − 18) — no scale required.
Blood Alcohol Concentration (BAC) Calculator
Estimate blood alcohol concentration (BAC %) with the Widmark formula from drinks consumed, body weight, sex and hours elapsed — and compare against the Hong Kong 0.05% drink-driving limit.
VO₂ Max Calculator (Cooper 12-Minute Run Test)
Enter your distance covered in a 12-minute run to estimate VO₂ max and read off the age/sex fitness category.