How to Use the Air Quality Mask Checker
A raw PM2.5 number from a sensor or app doesn't tell you much on its own — this calculator converts it into the EPA's official Air Quality Index (AQI), the 0-500 scale used on AirNow.gov, and translates that into a category and mask recommendation you can act on.
The EPA breaks PM2.5 concentrations (µg/m³) into ranges and maps each one to an AQI band: 0-9.0 is Good (AQI 0-50), 9.1-35.4 is Moderate (51-100), 35.5-55.4 is Unhealthy for Sensitive Groups (101-150), 55.5-125.4 is Unhealthy (151-200), 125.5-225.4 is Very Unhealthy (201-300), and 225.5 and above is Hazardous (301-500). The calculator interpolates within your concentration's range to compute the exact AQI number.
Mask guidance gets stricter as the category worsens. In the Moderate range, only sensitive groups — kids, older adults, and people with heart or lung conditions — need to think about a mask. Once you're in Unhealthy territory or above, a well-fitted N95 is recommended for everyone spending time outdoors, and at Very Unhealthy or Hazardous levels it's best to limit outdoor activity altogether.
Frequently Asked Questions
This calculator uses the EPA's official PM2.5 breakpoint table to convert your reading into a 0-500 AQI score and category, the same method used on AirNow.gov.
The EPA generally recommends sensitive groups (kids, older adults, people with heart or lung conditions) wear a well-fitted N95 starting around AQI 101, and everyone consider one above AQI 151.