AQI Calculator
Enter a raw pollutant concentration to calculate the corresponding US EPA Air Quality Index (AQI) value and health category.
Fine particulate matter ≤2.5 μm. 24-hour average concentration.
PM2.5 AQI Breakpoints
AQI Categories Reference
Air quality is satisfactory. Little or no risk.
Acceptable quality. Some risk for sensitive individuals.
General public is not likely affected. Sensitive groups may experience symptoms.
Everyone may experience health effects. Sensitive groups: more serious effects.
Health alert. Everyone may experience more serious health effects.
Health warning of emergency conditions. Everyone is more likely to be affected.
Frequently Asked Questions
How is AQI calculated from PM2.5?
The US EPA uses a piecewise linear formula: AQI = ((I_hi - I_lo) / (C_hi - C_lo)) × (C - C_lo) + I_lo, where C is the pollutant concentration and the breakpoints define the linear segments. Each segment maps a concentration range to an AQI range.
What is the difference between US AQI and India NAQI?
The US EPA AQI uses 6 categories (Good to Hazardous) on a 0–500 scale. India's National AQI (NAQI) also uses 6 categories (Good to Severe) on 0–500, but the breakpoints are different — India's scale is generally stricter for PM2.5 at low concentrations and more lenient at high concentrations.
What PM2.5 level is dangerous?
US EPA: PM2.5 above 55.4 μg/m³ (24-hr avg) is Unhealthy for Sensitive Groups. Above 125.5 μg/m³ is Unhealthy for everyone. The WHO guideline is much stricter: annual average below 5 μg/m³ and 24-hr average below 15 μg/m³.
Does AQI represent a mix of pollutants?
The reported AQI is always the maximum sub-index across all measured pollutants at a given location. Each pollutant is independently converted to its AQI equivalent, and the highest value is reported as the overall AQI.