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Air Quality Index Calculator

Work out air quality index instantly with clear inputs, formula shown and shareable results.

About Air Quality Index Calculator

The US EPA AQI maps PM2.5 concentration onto a 0-500 scale through piecewise linear breakpoints, so 35 ug/m3 gives an AQI of 99 - the top of the moderate band. That is more than twice the WHO 24-hour guideline of 15 ug/m3, which is stricter than the EPA breakpoints and is why national indices and WHO advice often disagree.

Formulas

EPA AQI interpolation

AQI = (Ihigh - Ilow) / (Chigh - Clow) x (C - Clow) + Ilow

PM2.5 breakpoints

0-12 good, 12.1-35.4 moderate, 35.5-55.4 unhealthy for sensitive groups

Worked example

With the default values below, Air Quality Index Calculator returns Air Quality Index of 99. Change any input above and every figure here is recalculated in your browser.

Inputs used

PM2.5 concentrationminimum 0 ug/m3
35 ug/m3
Index standardone of US EPA AQI, Simplified linear index
US EPA AQI

Results

Air Quality Index
99
AQI Category
Moderate
Times The WHO 24-Hour Guideline
2.33
PM2.5 Concentration
35.0 ug/m3

Step by step

  1. 1Values used
  2. 2EPA AQI interpolation
  3. 3PM2.5 breakpoints
  4. 4Air Quality Index= 99
  5. 5AQI Category= Moderate
  6. 6Times The WHO 24-Hour Guideline= 2.33
  7. 7PM2.5 Concentration= 35.0 ug/m3

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why do different countries report different AQI for the same air?

Because each sets its own breakpoints and averaging periods. India, China, the EU and the US all use different scales.

Is PM2.5 the only pollutant in the index?

No - ozone, nitrogen dioxide, sulfur dioxide, carbon monoxide and PM10 are each converted and the highest sub-index becomes the reported AQI.

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