Air quality tool
AQI Health Calculator
Enter an Air Quality Index value to see exactly what it means for health, who should limit outdoor activity, and how the EPA categorizes it.
According to the U.S. Environmental Protection Agency (EPA), 995 monitored counties and 501 metro areas reported Air Quality Index readings through the federal Air Quality System (AQS) for the 2024 reporting year. This tool reads those official records directly; see the methodology for how every figure is computed.
75 Moderate
Acceptable; unusually sensitive people should consider limiting prolonged outdoor exertion.
EPA AQI categories
| AQI range | Category | What it means |
|---|---|---|
| 0–50 | Good | Air quality is satisfactory; air pollution poses little or no risk. |
| 51–100 | Moderate | Acceptable; unusually sensitive people should consider limiting prolonged outdoor exertion. |
| 101–150 | Unhealthy for Sensitive Groups | People with heart or lung disease, older adults, children, and teens should reduce prolonged outdoor exertion. |
| 151–200 | Unhealthy | Everyone may begin to feel effects; sensitive groups feel more serious effects. |
| 201–300 | Very Unhealthy | Health alert: the risk of effects is increased for everyone. Avoid prolonged outdoor exertion. |
| 301–500 | Hazardous | Health warning of emergency conditions; everyone should avoid all outdoor exertion. |
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Frequently asked questions
How does the AQI health calculator work?
Enter any Air Quality Index value from 0 to 500 and the tool instantly shows the EPA category for that reading, its standard color code, and the health guidance the EPA publishes for that band, including which groups should limit outdoor activity. Nothing is sent to a server; the calculation runs in your browser.
What is the highest AQI value?
The Air Quality Index is defined on a 0 to 500 scale. Readings above 500 are described as “beyond the AQI” and occur only during extreme events such as major wildfire smoke; the EPA treats anything above 300 as hazardous and recommends everyone avoid outdoor exertion.
Which pollutant does the AQI represent?
On any given day the reported AQI reflects whichever criteria pollutant is worst at that location, most often ground-level ozone or fine particle pollution (PM2.5). The county and metro profiles on this site break down how many days each pollutant was the primary AQI driver.