Air Quality Index (AQI) Calculator
Six real national indices, each calculated its own way. Most free tools run the US EPA formula and call it “AQI” everywhere, which gives a user in Delhi, Toronto or London a number their own health advice does not use.
Which index?
Picked from your country by default
Same readings, a second country’s method, side by side
Advanced / Custom Input — the method
The 2024 revision lowered the PM2.5 “Good” ceiling from 12.0 to 9.0.
BC wildfire season: the published AQHI is the greater of the formula and ceiling(PM2.5 ÷ 10).
Particulate readings
Leave anything you have not measured at zero — it will be excluded rather than counted as clean.
24-hour average
µg/m³
24-hour average
µg/m³
Advanced / Custom Input — particulates
Only used by AQHI-Plus during wildfire season.
µg/m³
Gas readings
8-hour average
µg/m³
1-hour average
µg/m³
1-hour average
µg/m³
8-hour average
mg/m³
Advanced / Custom Input — units and averaging
The US EPA works in ppm/ppb; most other schemes use µg/m³. Conversion assumes 25 °C and 1 atm.
Mixing up averaging periods is the commonest real error here.
Who is this for?
Changes which advice line is shown, never the index
Advanced / Custom Input — reporting
Result
Put in the pollutant readings you have, then press “Work out the index”.
Estimate only — this tool does not fetch live data. For current readings check your local environmental agency’s monitoring site. Health advice here is general and is no substitute for medical guidance.