Two-way EPA converter
PM2.5 ↔ AQI converter
Use the current EPA PM2.5 breakpoints in either direction. Values above AQI 500 remain Hazardous and are clearly marked as an extrapolation outside the standard display scale.
Estimated PM2.5
55.4 µg/m³
Category
Unhealthy for Sensitive Groups
24-hour particulate equivalent
≈ 2.52 cigarettes
Interpolation band
AQI 101–150 / PM2.5 35.5–55.4 µg/m³
AQI-to-PM2.5 is an inverse estimate inside the relevant EPA breakpoint band; AQI itself is a rounded index.
Only use this conversion when the AQI is specifically for PM2.5. Ozone or overall AQI cannot be converted to a cigarette equivalent.
Formula version: EPA PM2.5 AQI — May 2026 · Reviewed: 2026-07-20
Current PM2.5 AQI breakpoints
| AQI | PM2.5 (µg/m³) |
|---|---|
| 0–50 | 0.0–9.0 |
| 51–100 | 9.1–35.4 |
| 101–150 | 35.5–55.4 |
| 151–200 | 55.5–125.4 |
| 201–300 | 125.5–225.4 |
| 301–500 | 225.5–325.4 |
Calculation method
For PM2.5 → AQI, concentration is truncated to one decimal, linearly interpolated inside its breakpoint band, then AQI is rounded to the nearest integer. The inverse direction estimates concentration from a rounded index.
Formula: EPA PM2.5 AQI — May 2026 · Reviewed: 2026-07-20
EPA/AirNow technical documentTrust Signals
Limits of AQI conversion
Review policy
July 20, 2026. We update supporting pages when calculator logic, live data behavior, or source framing changes.
Primary sources
AQI uses EPA / AirNow breakpoint logic. Cigarette-equivalent framing follows Berkeley Earth’s PM2.5 interpretation.
Live data layer
City pages use EPA AirNow where supported, with cached fallbacks and planning baselines if the API fails or coverage is unavailable.
Conversion questions
Can overall AQI be converted to PM2.5?
Only if the reported pollutant is PM2.5. Overall AQI may be driven by ozone or another pollutant.
What happens above AQI 500?
The standard display scale ends at 500. This tool supports searched values through 700 by extending the 301–500 PM2.5 line with the same slope and labeling it as an estimate.
Why does 9.09 become 9.0?
EPA requires PM2.5 concentration to be truncated, not rounded, to one decimal before calculating AQI.