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), 977 monitored counties and 496 metro areas reported Air Quality Index readings through the federal Air Quality System (AQS) for the 2025 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.

More ways to explore

AQI lookupFind any county’s real median AQI. Compare countiesPut counties side by side. Understanding the AQIA plain-language guide to the index. Air pollution & healthWho is most at risk and why. Common pollutantsOzone, PM2.5, and the rest. MethodologyHow the AQI is computed.

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.

Every figure on PlainAir is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.