No. You cannot responsibly convert every number labeled “AQI” into cigarette-equivalents.
This site's AQI conversion is valid only when the input is a U.S. PM2.5 AQI. If the value is driven by ozone, comes from another index, or does not identify a pollutant, converting it as PM2.5 invents a particle concentration that the source never reported.
Use this page as a pre-conversion checklist.
Why the pollutant matters
The U.S. EPA calculates a separate AQI sub-index for each covered pollutant. The overall AQI is the highest of those sub-indexes. In the EPA's 2026 AQI technical document, the example with ozone, PM2.5, and carbon monoxide reports the highest value—ozone—as the overall AQI.
An overall AQI of 126 therefore does not uniquely identify a PM2.5 concentration. It could be:
- an ozone AQI of 126;
- a PM2.5 AQI of 126;
- a PM10 or another pollutant sub-index; or
- the highest of several different sub-indexes.
The same AQI number maps to different physical units and pollutant breakpoints. Treating an ozone AQI as PM2.5 is not an approximation; it is the wrong conversion.
The eligibility checklist
Before entering an AQI, answer all three questions.
1. Is it on the U.S. AQI scale?
Countries and providers use different air-quality indexes. They may include different pollutants, average over different time periods, and place category boundaries at different concentrations. Google's official index comparison documents several of these differences.
Look for an explicit label such as U.S. AQI, US EPA AQI, or AirNow AQI. A scale that also runs from 0 upward is not necessarily equivalent.
If the source uses another national or regional index, do not enter that index value. Look for the underlying PM2.5 concentration instead.
2. Is the value specifically for PM2.5?
Look for one of these labels:
- PM2.5 AQI;
- AQI (PM2.5);
- main or dominant pollutant: PM2.5; or
- an individual PM2.5 sub-index.
If the screen says only “AQI” and does not identify the pollutant, treat it as unknown. Open the details, use a pollutant layer, or consult the provider's documentation.
3. Does the value represent the scenario you want to compare?
Check location, timestamp, and whether the number is a current observation, NowCast, forecast, or historical daily AQI. A city-center forecast is not a measurement of the air inside your home. A nearby ten-minute sensor reading and a daily AQI do not describe the same time window.
The cigarette-equivalent formula scales a concentration by the duration you enter. It does not reconstruct your movement, breathing rate, indoor infiltration, or personal dose.
If any answer is “no” or “unknown,” stop and obtain a better input.
Preferred inputs, from most direct to least direct
Direct PM2.5 concentration in µg/m³
When a reliable source provides PM2.5 mass concentration, use the PM2.5 Cigarette Calculator. This avoids reversing a rounded AQI back into concentration.
Confirm that the number is an average appropriate to your scenario, not a momentary spike. Consumer optical sensors can be affected by placement, humidity, particle composition, and correction settings. Trends across multiple readings are usually more useful than one isolated value.
Confirmed U.S. PM2.5 AQI
Use the AQI to Cigarettes Calculator when the source explicitly reports U.S. PM2.5 AQI. The calculator uses EPA's current PM2.5 breakpoints to estimate concentration, then applies the Berkeley Earth communication benchmark.
Because AQI is rounded, the reverse-converted concentration is approximate.
Unknown overall AQI
Do not convert it. The unknown pollutant makes the PM2.5 concentration indeterminate.
Inputs that must not be converted as PM2.5
Ozone AQI
Ozone is a gas reported in concentration units and averaging periods different from PM2.5. Ozone can drive summer AQI even when particle concentrations are relatively low. Use AirNow's ozone health guidance rather than a cigarette-equivalent conversion.
PM10 AQI
PM10 includes particles up to 10 micrometers and has its own EPA breakpoints. A PM10 AQI cannot be used as a PM2.5 AQI, even though both are particle pollution.
Smoke plume graphics or fire icons
A satellite-detected fire or NOAA smoke plume indicates fire or smoke information, not a measured PM2.5 concentration at your location. On the AirNow Fire and Smoke Map, use a nearby measurement icon and inspect its details instead.
Indoor “AQI” with no documented formula
Some monitors create a proprietary indoor score or apply an AQI formula to a very short PM2.5 average. Check the manual for pollutant, units, averaging period, scale, and correction. A low indoor particle value also says nothing about carbon monoxide, radon, ozone, or VOCs.
A forecast from another AQI system
A forecast is already uncertain, and the wrong index adds a second mismatch. If you are planning future exposure, use the forecast category for preparation and recheck current PM2.5 when the time arrives.
What the calculator actually does
The AQI route has two transparent steps.
First, it estimates PM2.5 concentration by linearly interpolating within EPA's current U.S. PM2.5 AQI breakpoints. The revised breakpoints took effect on May 6, 2024; the current May 2026 technical document reproduces them. For example, AQI 101–150 maps to 35.5–55.4 µg/m³.
Second, it applies the Berkeley Earth cigarette-equivalence benchmark:
Cigarette-equivalents = (PM2.5 µg/m³ / 22) × (hours / 24)
At a confirmed PM2.5 AQI of 150, the estimated concentration is about 55.4 µg/m³. For eight hours:
(55.4 / 22) × (8 / 24) = 0.84 cigarette-equivalents
That is a population-level risk-communication heuristic. It is not the number of cigarettes smoked, an inhaled-dose estimate, or a personal medical prediction. Read the science and limitations for the complete boundary.
A decision tree for common screens
The app shows “AQI 140, main pollutant PM2.5, U.S. AQI.”
Eligible for a rough AQI conversion. Check time, location, and duration.
The app shows “AQI 140, main pollutant ozone.”
Do not convert. Follow ozone-specific guidance.
The app shows “AQI 140” with no pollutant.
Open the pollutant details. If PM2.5 cannot be confirmed, do not convert.
A sensor shows “PM2.5 42 µg/m³.”
Use the direct PM2.5 calculator after checking averaging period, placement, and correction.
Two apps show different AQI values.
Use the app disagreement checklist to match index, pollutant, location, timestamp, and method before choosing an input.
Why a conservative gate improves the result
Refusing an ineligible input is more accurate than producing a precise-looking answer from it. The arithmetic can be correct while the premise is false.
This gate also keeps two different decisions separate:
- AQI health categories tell you how to adjust activity for a specific pollutant and population group.
- The cigarette-equivalent result communicates the rough scale of a confirmed PM2.5 concentration-and-time scenario.
For immediate health decisions, use AirNow AQI guidance and local alerts. Do not use the cigarette-equivalent output as a safe/unsafe threshold.
Bottom line
Convert only a value explicitly identified as U.S. PM2.5 AQI. Prefer direct PM2.5 in µg/m³ when it is available. Reject ozone, PM10, unknown overall AQI, foreign indexes, and undocumented proprietary scores.
The result is more trustworthy when the calculator sometimes says “this input cannot be converted.”