Smog Calculator (air pollution as cigarettes smoked per day)

Understanding the air pollution cigarette equivalent calculator — concept and principle

This calculator turns a PM2.5 fine-particle level into an approximate "cigarettes per day" equivalent, following a Berkeley Earth comparison, and compares the level with the WHO air quality guidelines. It is a way to picture long-term health risk from polluted air.

Fine dust as cigarettes: with the default inputs the result is ≈ 48 cigarettes (2.4 packs in 30 days).

How it is calculated

Cigarette equivalent per day = PM2.5 (µg/m³) ÷ 22.
Over a period = per day × days; packs = cigarettes ÷ 20.
Per year at this level = per day × 365.
Times the WHO annual guideline = PM2.5 ÷ 5; times the 24-hour guideline = PM2.5 ÷ 15.

The principle

Fine particles (PM2.5) are small enough to reach deep into the lungs and the bloodstream, and long-term exposure is linked to heart and lung disease. Berkeley Earth compared estimated deaths from air pollution with deaths from smoking and concluded that breathing air with about 22 µg/m³ of PM2.5 for a day carries roughly the same risk as smoking one cigarette. The comparison is a rough way to picture risk: it was derived from average yearly exposure across whole populations and assumes all particles are equally harmful. The WHO 2021 guidelines set 5 µg/m³ as a yearly mean and 15 µg/m³ as a 24-hour mean.

Worked example

Default inputs: PM2.5 35 µg/m³ for 30 days.

Per day = 35 ÷ 22 = 1.6 cigarettes.
Over 30 days = 1.59 × 30 = 48 cigarettes = 2.4 packs.
Times WHO annual guideline = 35 ÷ 5 = 7×; times 24-hour guideline = 35 ÷ 15 = 2.33×.
At this level all year = 1.59 × 365 = 581 cigarettes.

Each point is the calculator re-run with only “PM2.5 concentration (µg/m³)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

PM2.5 concentration (µg/m³)	Cigarette equivalent per day
8.75	0.4
17.5	0.8
26.2	1.2
35	1.6
43.8	2
52.5	2.4
70	3.2

How to read the result

Where does your result fall?

The figure is a way to picture risk, not a measure of your personal dose: time indoors, filters, masks and activity level all change what you breathe. Use local air-quality forecasts to reduce exposure on bad days, for example by limiting hard outdoor exercise and using an air purifier indoors.

Common mistakes

Treating the comparison as exact or as a medical diagnosis.
Applying it to a single hour of exposure.
Comparing a 1-hour reading with the 24-hour or yearly guideline.
Assuming indoor air equals outdoor air.

Keep in mind: This is not a diagnosis or medical advice. People with heart or lung conditions, children, older adults and pregnant people are more vulnerable; follow local health advice on high-pollution days.

Frequently asked questions

How many cigarettes is PM2.5 of 35 equal to?

About 1.6 cigarettes a day under the Berkeley Earth comparison.

What is the WHO PM2.5 guideline?

5 µg/m³ as a yearly mean and 15 µg/m³ as a 24-hour mean (2021).

Is the cigarette comparison exact?

No. It is a rough picture of long-term risk across populations.

Sources: R. A. Muller & E. A. Muller, "Air Pollution and Cigarette Equivalence", Berkeley Earth memo (2015) · World Health Organization, WHO global air quality guidelines (2021)

Checked 9 Nov 2026. R. A. Muller & E. A. Muller, “Air Pollution and Cigarette Equivalence”, Berkeley Earth memo (2015): 1 cigarette per day ≈ 22 µg/m³ PM2.5; WHO global air quality guidelines (2021): PM2.5 5 µg/m³ annual and 15 µg/m³ 24-hour.

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