Free tool · US EPA 2024 and India CPCB
AQI calculator Convert PM2.5 and other pollutants to the AQI
Turn a reading from a sensor or a report into the Air Quality Index, or an AQI back into micrograms. It uses the same tables and rounding as every reading on Airleaf.
The AQI is a score for how polluted the air is, and lower is better: 0–50 is Good, above 150 is unhealthy for everyone, and above 300 is Hazardous.
- pollutants: PM2.5, PM10, ozone, NO₂, SO₂, CO
- 6
- scales: the US EPA's and India's
- 2
- the EPA's latest PM2.5 table
- 2024
- no sign-up, works on a phone
- Free
AQI calculator
US AQI 99: Moderate
PM2.5 35 µg/m³ (24-hour average)
Unusually sensitive people should consider limiting long outdoor exertion.
On India's CPCB scale the same PM2.5 reads 58, “Satisfactory”.
How the AQI is calculated
Each pollutant gets its own score from the EPA's table. The concentration is truncated first (PM2.5 to one decimal, PM10 and the gases to whole numbers, CO to one decimal of a ppm), placed in the row whose range contains it, and scaled along that row:
AQI = (Ihigh − Ilow) ÷ (Chigh − Clow) × (C − Clow) + Ilow
The AQI you see is the highest of the pollutants' scores, and that pollutant is the “main pollutant”. On most bad-air days it is PM2.5. The tables assume an averaging period: 24 hours for particles, 8 hours for ozone and carbon monoxide, 1 hour for nitrogen dioxide and sulfur dioxide.
US EPA AQI breakpoints (2024)
| AQI | PM2.5µg/m³, 24-hour | PM10µg/m³, 24-hour | Ozoneppb, 8-hour | Nitrogen dioxideppb, 1-hour | Sulphur dioxideppb, 1-hour | Carbon monoxideppm, 8-hour |
|---|---|---|---|---|---|---|
| 0–50Good | 0.0–9.0 | 0–54 | 0–54 | 0–53 | 0–35 | 0.0–4.4 |
| 51–100Moderate | 9.1–35.4 | 55–154 | 55–70 | 54–100 | 36–75 | 4.5–9.4 |
| 101–150Unhealthy for sensitive groups | 35.5–55.4 | 155–254 | 71–85 | 101–360 | 76–185 | 9.5–12.4 |
| 151–200Unhealthy | 55.5–125.4 | 255–354 | 86–105 | 361–649 | 186–304 | 12.5–15.4 |
| 201–300Very unhealthy | 125.5–225.4 | 355–424 | 106–200 | 650–1249 | 305–604 | 15.5–30.4 |
| 301–500Hazardous | 225.5–325.4 | 425–604 | — | 1250–2049 | 605–1004 | 30.5–50.4 |
Source: US EPA, Technical Assistance Document for the Reporting of Daily Air Quality (May 2024). Ozone above 200 ppb is scored on its 1-hour average, which the 8-hour table above does not cover.
India's AQI (CPCB) for particles
| AQI | PM2.5 (µg/m³, 24-hour) | PM10 (µg/m³, 24-hour) |
|---|---|---|
| 0–50 Good | 0–30 | 0–50 |
| 51–100 Satisfactory | 31–60 | 51–100 |
| 101–200 Moderate | 61–90 | 101–250 |
| 201–300 Poor | 91–120 | 251–350 |
| 301–400 Very poor | 121–250 | 351–430 |
| 401–500 Severe | above 250 | above 430 |
The two scales cross near 80 µg/m³ of PM2.5: below it the US AQI reads higher, above it India's does. Why CPCB and IQAir show different numbers
Clean-air buying guides
Bring the AQI down indoors
A monitor shows the AQI inside your home; a purifier sized by its tested clean-air delivery rate (CADR) brings it down. No brand pays to be listed.
- The best PM2.5 monitors for smoke and smog at home
Home monitors with laser PM2.5 sensors that show whether smoke and smog are getting in, and whether your purifier is keeping up.
- The best air purifiers for wildfire smoke and smog
Air purifiers that keep up with wildfire smoke and winter smog, ranked by verified smoke CADR, with the room each one clears on a smoky day.
- NIOSH-approved N95 masks for smoke and smog
NIOSH-approved N95 masks and P100 respirators for smog and smoke, and how to get the fit right. Cloth and surgical masks do little against PM2.5.
Frequently asked
AQI questions
How do you convert PM2.5 to AQI?
Find the row of the EPA table whose concentration range contains your PM2.5 (truncated to one decimal), then interpolate: AQI = (I_high − I_low) / (C_high − C_low) × (C − C_low) + I_low, rounded to a whole number. For example, 20 µg/m³ sits in the 9.1–35.4 row (AQI 51–100), which gives an AQI of 71. The table assumes a 24-hour average; applied to a single hour it overstates a short spike.
What PM2.5 level is unhealthy?
On the US scale, PM2.5 above 35.4 µg/m³ is unhealthy for sensitive groups (AQI 101–150), and above 55.4 µg/m³ unhealthy for everyone (AQI 151 and up). Only 9.0 µg/m³ or less counts as good. The World Health Organization's guideline is stricter: 15 µg/m³ as a 24-hour average and 5 µg/m³ over a year.
What changed in the 2024 AQI update?
In 2024 the US EPA revised its PM2.5 breakpoints. The top of "Good" fell from 12.0 to 9.0 µg/m³, the "Unhealthy" and "Very unhealthy" rows were lowered, and "Hazardous" became a single 301–500 row for every pollutant. The same air can therefore read a little higher than it did under the 2012 table. IQAir, AirNow and Airleaf all use the 2024 rows.
Why does my sensor show a different AQI from the official one?
Mostly averaging. The AQI tables are built for 24-hour averages of particles, while a home sensor or app shows the latest minutes or hour, and official agencies often publish the 24-hour figure or the EPA's NowCast, which weights recent hours. Low-cost sensors also read high in humid air unless they are corrected. And many countries publish their own index: India's, Malaysia's and Singapore's read the same air differently from the US scale.
Can the AQI go above 500?
Yes. 500 is the top of the table, not a ceiling on the air. Past it the EPA continues the top row's line, so dense smoke from peat or forest fires can score well above 500. Readings that high are rare and always hazardous.