Enter one or more pollutant concentrations to estimate the U.S. Air Quality Index (AQI). The highest sub-index becomes your overall AQI and identifies the dominant pollutant.
What is the Air Quality Index (AQI)?
The Air Quality Index is a simple 0-500 scale that translates pollutant concentrations into a single, easier-to-read number. Instead of asking people to interpret raw PM2.5 or ozone data, AQI maps those numbers into health risk categories such as Good, Moderate, and Unhealthy.
In practice, AQI helps families make day-to-day decisions: whether to exercise outside, keep windows open, use an air purifier, or reschedule outdoor activities for children, older adults, and people with asthma or heart disease.
How this AQI calculator works
Each pollutant has published breakpoint ranges. For example, a PM2.5 concentration between 12.1 and 35.4 µg/m³ maps to an AQI between 51 and 100. The calculator uses linear interpolation inside that interval:
AQI = (Ihigh − Ilow) / (Chigh − Clow) × (C − Clow) + Ilow
- C = your measured concentration
- Clow, Chigh = concentration breakpoints
- Ilow, Ihigh = AQI breakpoints
After the calculator computes a sub-index for each pollutant you entered, the highest sub-index becomes the overall AQI. That pollutant is shown as the dominant pollutant.
AQI categories and health meaning
1) Good (0-50)
Air quality is considered satisfactory, and air pollution poses little or no risk for most people.
2) Moderate (51-100)
Air quality is acceptable for many people, but there may be a minor concern for unusually sensitive individuals.
3) Unhealthy for Sensitive Groups (101-150)
People with asthma, chronic lung disease, cardiovascular conditions, children, and older adults should reduce prolonged outdoor exertion.
4) Unhealthy (151-200)
Some members of the general public may begin to experience health effects, and sensitive groups may experience more serious effects.
5) Very Unhealthy (201-300)
Health alert: the risk of health effects increases for everyone.
6) Hazardous (301-500)
Emergency conditions. Everyone is more likely to be affected, and exposure should be minimized.
Practical steps when AQI rises
- Reduce outdoor intensity and duration, especially for runs, biking, and field sports.
- Keep windows closed during peak pollution hours; use filtered ventilation when possible.
- Run a HEPA air purifier in bedrooms and main living areas.
- Avoid additional indoor pollution sources (candles, smoke, heavy frying).
- Use well-fitted respirators (for example, N95-level) when high smoke or dust is unavoidable.
- Track local hourly changes—AQI can improve significantly at different times of day.
Important limitations
This tool estimates AQI from entered values and does not replace official station reports, regulatory guidance, or medical advice. AQI may differ based on averaging period, monitor method, local meteorology, and regional reporting standards. For legal or health-critical decisions, use your local environmental agency’s official dashboard.