Simple Calculator Tools

Air Quality Index (AQI) Calculator

Enter a raw pollutant concentration and convert it into an Air Quality Index value and health category using the EPA's piecewise-linear formula.

Pollutant reading

Choose a pollutant and enter the measured concentration.

Air Quality Index—Select a pollutant and enter a concentration above.
Category—
Breakpoint range used—
Quick insight

Air Quality Index (AQI) Calculator

Select a pollutant and enter a concentration to see the equivalent AQI.

🤖
Powered by SCT Smart Guide™

Let’s understand your Air Quality Index (AQI) Calculator result.

Ready
Your personalized explanation

Use the calculator, then select an option above.

What Is an Air Quality Index Calculator?

The Air Quality Index (AQI) is a standardized 0-500 scale that U.S. environmental agencies use to translate raw pollutant measurements into a single, easy-to-understand health number. This calculator applies the EPA's official piecewise-linear breakpoint formula to convert a measured concentration of PM2.5, PM10, ozone or carbon monoxide into its equivalent AQI value and health category.

Because each pollutant has its own health effects and measurement units, the EPA maintains separate breakpoint tables for each one. The formula linearly interpolates between the two breakpoints that bracket your reading, which is exactly how official AQI values reported by monitoring stations are calculated.

How to Read Your Results

Air Quality Index

Your calculated AQI value, rounded to the nearest whole number, on the standard 0-500 scale used across all pollutants.

Category

The health category associated with your AQI value, ranging from Good (0-50) to Hazardous (401-500). Categories from Moderate upward increasingly recommend limiting outdoor exertion for sensitive groups and eventually everyone.

Breakpoint Range Used

Shows exactly which pair of table breakpoints your concentration fell between, so you can see how the interpolation was calculated.

Real-World Example

Suppose a monitoring station reports a 24-hour average PM2.5 concentration of 40.0 µg/m³.

InputValue
PollutantPM2.5
Concentration40.0 µg/m³
Breakpoint range35.5–55.4 µg/m³ → AQI 101–150
Calculated AQI≈110 (Unhealthy for Sensitive Groups)

At this level, people with asthma, heart or lung disease, older adults and children are advised to reduce prolonged or heavy outdoor exertion, even though the general public isn't yet significantly affected.

Tips for Interpreting AQI

  • AQI is not linear across pollutants — an AQI of 100 from ozone and an AQI of 100 from PM2.5 reflect different underlying concentrations relative to each pollutant's own health thresholds.
  • Averaging periods differ by pollutant. PM2.5 and PM10 use 24-hour averages, while ozone and CO in this table use 8-hour averages.
  • Breakpoint tables are updated periodically by regulators as health research evolves — always confirm against your local agency's current table for anything safety-critical.
  • Sensitive groups should act at lower AQI values than the general population, typically starting around AQI 101.

Related Calculators

Combined Noise Level Decibel Addition Calculator

Recommended resources

Relevant offers are selected by the existing Smart Affiliate Manager for this calculator topic.

Note: This calculator uses widely-published EPA breakpoint tables for estimation and education. Official breakpoints are periodically revised by regulators (most recently for PM2.5); for regulatory, medical or emergency decisions always use your local environmental agency's current official AQI reporting, such as AirNow.gov.

Last updated: August 2026 · Reviewed by: Simple Calculator Tools Editorial Team