AQI calculator: convert PM2.5 and other pollutant readings to an air quality index
This AQI calculator turns the pollutant concentrations printed by an air monitor or a sensor app into an air quality index number, a category and the health advice that goes with it. Pick the India National AQI used by CPCB, or the US EPA AQI, type in PM2.5, PM10 and any gases you have, and the page shows the sub-index of each pollutant, which one sets the overall figure, and what the agency says that level means for people.
A common question is what a PM2.5 reading of 180 µg/m³ actually means. On the India scale it is about 346, in the Very Poor band; on the US scale the same number is about 255, Very Unhealthy. The two scales use different breakpoints, so the same air can have two different AQI values. The tool shows both for PM2.5 so you can see why.
How to calculate AQI
- Choose the India NAQI (CPCB) or the US EPA AQI.
- Enter PM2.5 and PM10 in µg/m³. These are 24-hour averages in both systems.
- Add the gases you have. India uses NO₂, SO₂, NH₃, Pb and O₃ in µg/m³ and CO in mg/m³; the US scale uses ozone, CO, SO₂ and NO₂ in ppb or ppm.
- Read the overall AQI, its category and the main pollutant, then the health note below it.
- Copy the summary if you want to share the figures.
What this AQI calculator does
Two official scales
India NAQI with eight pollutants and six bands from Good to Severe, and the US EPA AQI with six pollutants and bands from Good to Hazardous.
Sub-index per pollutant
Each reading is converted by straight-line interpolation between the published breakpoints, and the highest sub-index becomes the AQI.
Honest about missing data
India’s method needs at least three pollutants including PM2.5 or PM10. With fewer, the page labels the answer as indicative.
Health advice from the agencies
Messages come from CPCB’s health statements and the US EPA’s cautionary statements, not from us.
How the AQI is worked out
- Sub-index. For each pollutant the tool finds the two breakpoints around your concentration and interpolates: I = (I_high − I_low) ÷ (BP_high − BP_low) × (C − BP_low) + I_low. This is equation 4 of the CPCB report and equation 1 of the EPA document.
- Overall AQI. The overall figure is the highest sub-index. CPCB calls this the maximum operator; the EPA calls the winning pollutant the main pollutant.
- EPA rounding. The EPA truncates concentrations first (PM2.5 to one decimal, PM10 to a whole number, CO to one decimal, ozone to three decimals in ppm) and rounds the index to the nearest integer. This tool does the same.
- India above the top breakpoint. The CPCB report publishes no upper limit for Severe. We continue the Very Poor slope and stop at 500, and say so on the page.
PM2.5 breakpoints side by side (µg/m³, 24-hour)
India’s scale has bands of 0–50, 51–100, 101–200, 201–300, 301–400 and 401–500, so an Indian “Moderate” (101–200) is wider than the US “Moderate” (51–100). Sources and dates are listed at the end of this section.
| Band | India NAQI (CPCB 2014) | US EPA (2024 update) |
|---|---|---|
| Good | 0–30 (AQI 0–50) | 0–9.0 (0–50) |
| Satisfactory / Moderate | 31–60 (51–100) | 9.1–35.4 (51–100) |
| Moderate / Unhealthy for Sensitive Groups | 61–90 (101–200) | 35.5–55.4 (101–150) |
| Poor / Unhealthy | 91–120 (201–300) | 55.5–125.4 (151–200) |
| Very Poor / Very Unhealthy | 121–250 (301–400) | 125.5–225.4 (201–300) |
| Severe / Hazardous | above 250 (401–500) | 225.5 and above (301+) |
Sources, dates and limits
- India: CPCB, “National Air Quality Index” report (2014, expert group with IIT Kanpur), Tables 3.11 and 3.12, read on 30 October 2026 at cpcb.gov.in. CPCB says it may review breakpoints every three years; check for a newer revision.
- United States: US EPA, “Technical Assistance Document for the Reporting of Daily Air Quality – the Air Quality Index (AQI)”, EPA-403/B-26-003, May 2026, Tables 5 and 6, which include the PM2.5 breakpoints revised in 2024 (a 24-hour value of 9.0 µg/m³ is now the top of Good).
- This tool takes one value per pollutant. It does not compute NowCast, the EPA’s hourly weighting, or the 1-hour ozone index used above 300. Ozone above 200 ppb is shown as 301+.
- Low-cost sensors can read differently from regulatory monitors, so a phone-app AQI can disagree with an official station.
- This is information, not medical advice. If you have heart or lung disease, or symptoms, talk to a doctor.
AQI Calculator FAQ
What is the AQI for PM2.5 of 180?
About 346 on the India NAQI, which is Very Poor, and about 255 on the US EPA scale, which is Very Unhealthy. Both are worked out by interpolating between the agency breakpoints.
Why does the same PM2.5 give two different AQI values?
India and the US use different breakpoints and different category widths. For example, PM2.5 of 60 µg/m³ is 100 in India but 154 in the US.
How many pollutants does the Indian AQI need?
CPCB says the AQI can be calculated when data exist for at least three pollutants, one of which must be PM2.5 or PM10. This tool still lets you try one, but marks it indicative.
Is the AQI the average of the pollutants?
No. It is the worst (highest) sub-index, so one bad pollutant sets the number.
Are the values hourly or daily?
PM and most gases use 24-hour averages in India; CO and ozone use 8-hour averages. The US scale uses 24-hour PM, 8-hour CO and ozone, and 1-hour SO₂ and NO₂.
Which AQI should I follow in India?
Use the CPCB National AQI, which is what Indian stations and apps report. The US figure is shown only for comparison.