AQI Calculator
Calculate and compare air-quality classifications using official U.S., Indian and European reference methods. Enter pollutant concentrations, see the result, then open the calculation to understand how it was derived.
Use matching data: averaging period and units matter. This educational calculator estimates an index from the concentrations you enter; it does not turn an instantaneous sensor reading into an official daily AQI.
How the U.S. AQI is calculated
Iₚ = [(IHi − ILo) ÷ (BPHi − BPLo)] × (Cₚ − BPLo) + ILo
EPA first prepares the pollutant concentration to the precision required by its methodology, finds the concentration breakpoints containing that value and interpolates the pollutant sub-index. The highest valid pollutant AQI becomes the overall AQI.
Cₚ = pollutant concentration; BP = concentration breakpoints; I = AQI breakpoints. EPA's official daily AQI uses prescribed averaging and reporting rules; a single instantaneous sensor value is not automatically an official daily AQI.
How India's National AQI is calculated
Iₚ = [(IHI − ILO) ÷ (BHI − BLO)] × (Cₚ − BLO) + ILO
Overall AQI = max(Iₚ)
CPCB calculates a sub-index for each available pollutant by interpolating between the surrounding concentration and index breakpoints. The highest valid pollutant sub-index determines the National AQI. India uses six categories from Good to Severe.
The National AQI covers PM10, PM2.5, NO₂, SO₂, CO, O₃, NH₃ and Pb, with pollutant-specific averaging periods and official data-availability requirements.
How the European AQI is derived
Overall European AQI = poorest band among PM2.5, PM10, NO₂, O₃ and SO₂
The European Air Quality Index is not a U.S.-style 0–500 number. EEA places hourly concentrations into six bands: Good, Fair, Moderate, Poor, Very Poor and Extremely Poor. The poorest pollutant level becomes the overall index.
This difference is important: the European result is a category, not a numerical U.S.-style AQI produced by forcing European data into a 0–500 equation.
AQI standard and data source are different things
Monitoring networks measure pollutant concentrations; an AQI methodology determines how those measurements are interpreted. Data platforms such as WAQI and OpenAQ can make monitoring information easier to access, but they should not be confused with the organizations that operate the underlying monitoring stations. In India, many official measurements originate from CPCB, State Pollution Control Boards and other public monitoring networks.
OpenAQ primarily distributes physical pollutant measurements from upstream sources; an OpenAQ measurement from India does not automatically mean that the station follows the U.S. EPA AQI. Where AirQualityIndex.org converts concentrations for global comparison, the selected AQI method must be identified separately from the measurement source.
There is no single worldwide AQI formula. National and regional authorities may classify the same concentration differently. Use the calculator tabs above to compare the methods without treating unlike indexes as identical.
What method do WHO and the United Nations use?
The World Health Organization publishes health-based air-quality guidelines and, in 2026, a dedicated review of air-quality indexes. WHO distinguishes conventional indexes—often driven by the pollutant with the poorest level—from emerging health-based multi-pollutant indexes. WHO does not prescribe a single universal 0–500 AQI for every country. UN environmental and health work likewise does not replace national AQI systems with one universal UN numerical index.
What does your result mean?
The category shown by the calculator belongs to the method you selected. A U.S. AQI of 100, an Indian AQI of 100 and a European category should not be assumed to represent identical pollutant concentrations or health communication. For causes of high PM2.5, PM10, ozone and other pollutants, health context and practical interpretation, continue to Air Quality Explained.