PM2.5 to AQI Converter

Enter your PM2.5 reading and breakpoint segment values to calculate the corresponding Air Quality Index score and health category.

Created by Luis GonzalezLast updated: May 9, 2026

How to Use This Calculator

1
Enter PM2.5 Concentration
Input the measured PM2.5 particle concentration in micrograms per cubic metre (µg/m³).
2
Specify Breakpoint Low
Enter the lower PM2.5 concentration breakpoint for the relevant AQI segment (e.g., 12.1 µg/m³ for 'Moderate').
3
Specify Breakpoint High
Enter the upper PM2.5 concentration breakpoint for the relevant AQI segment (e.g., 35.4 µg/m³ for 'Moderate').
4
Enter AQI Low
Input the lower AQI index value corresponding to your chosen breakpoint segment (e.g., 51 for 'Moderate').
5
Enter AQI High
Input the upper AQI index value for your chosen breakpoint segment (e.g., 100 for 'Moderate').
6
View Estimated AQI and Category
The calculator will display the estimated Air Quality Index (AQI) value, the corresponding air quality category, and details about its position within the segment.

Example Calculation

A local air quality monitor reports a PM2.5 concentration of 18.0 µg/m³. The user wants to convert this to AQI using the EPA's 'Moderate' category breakpoints (12.1-35.4 µg/m³ for PM2.5, corresponding to AQI 51-100).

PM2.5 Concentration (µg/m³)

18.0

Breakpoint Low (µg/m³)

12.1

Breakpoint High (µg/m³)

35.4

AQI Low

AQI High

100

Results

Tips

Use Real-Time Local Data

For the most accurate AQI, use current PM2.5 readings from local air quality monitoring stations (e.g., PurpleAir, AirNow.gov). These often update hourly and reflect immediate conditions, which can fluctuate rapidly.

Understand the Health Implications of Categories

An AQI between 51-100 ('Moderate') is generally acceptable, but sensitive groups should consider limiting prolonged outdoor exertion. Above 101 ('Unhealthy for Sensitive Groups'), everyone may start to experience adverse effects.

Verify Breakpoints with EPA Standards

Always cross-reference the breakpoint values you use with the latest US EPA standards. These can be updated periodically, and using outdated breakpoints will yield inaccurate AQI conversions, especially as of 2025.

Decoding Air Quality: Your PM2.5 to AQI Converter

The PM2.5 to AQI Converter Calculator is a critical tool for understanding local air quality by transforming raw PM2.5 (fine particulate matter) concentrations into the universally recognized Air Quality Index (AQI). Using EPA's linear interpolation breakpoints, it provides an estimated AQI value, its corresponding air quality category, and its position within that segment. For instance, a PM2.5 concentration of 18.0 µg/m³ falls into the 'Moderate' category with an AQI of 64, offering clear guidance on potential health risks in 2025.

Why Converting PM2.5 to AQI is Essential

Converting raw PM2.5 concentrations into the Air Quality Index (AQI) is essential because it simplifies complex scientific data into an easily understandable format for the public. While environmental scientists work with micrograms per cubic meter (µg/m³), the general population needs a clear, color-coded scale to assess daily air quality and make informed decisions about outdoor activities. The AQI provides a standardized, actionable health message, allowing sensitive groups to take precautions when air quality deteriorates, thereby protecting public health from the adverse effects of air pollution.

The EPA's Linear Interpolation for AQI Conversion

The conversion of PM2.5 concentration to AQI values is performed using a piecewise linear interpolation method as established by the US Environmental Protection Agency (EPA). This method maps a pollutant's concentration within a specific breakpoint range to its corresponding AQI range. The formula ensures a smooth, continuous transition between air quality categories.

AQI = ((AQI_high - AQI_low) / (BP_high - BP_low)) × (PM2.5 - BP_low) + AQI_low

Here, PM2.5 is the measured concentration, BP_low and BP_high are the lower and upper PM2.5 breakpoints for a given category, and AQI_low and AQI_high are the corresponding AQI index values. This formula ensures that the calculated AQI accurately reflects the health implications of the PM2.5 concentration.

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Practical Example: Assessing Moderate Air Quality

Let's say a local air quality sensor reports a PM2.5 concentration of 18.0 µg/m³. We want to convert this to an AQI using the EPA's breakpoints for the "Moderate" category:

PM2.5 Concentration: 18.0 µg/m³
Breakpoint Low (BP_low): 12.1 µg/m³
Breakpoint High (BP_high): 35.4 µg/m³
AQI Low (AQI_low): 51
AQI High (AQI_high): 100

Calculate AQI: AQI = ((100 - 51) / (35.4 - 12.1)) × (18.0 - 12.1) + 51 AQI = (49 / 23.3) × (5.9) + 51 AQI = 2.103 × 5.9 + 51 AQI = 12.4077 + 51 AQI = 63.4077
Round to Nearest Integer: Rounded AQI = 64
Determine Air Quality Category: An AQI of 64 falls into the "Moderate" category.

The primary result is an Estimated AQI of 64, placing the air quality in the "Moderate" category, indicating generally acceptable air but with potential risk for very sensitive individuals.

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The Historical Context of the Air Quality Index

The concept of an Air Quality Index (AQI) emerged in the United States in the early 1970s, spurred by growing public concern over air pollution and the need for a standardized, easily digestible way to communicate complex environmental data. Initially, various cities and states used different methods to report air quality, leading to confusion. In 1976, the U.S. Environmental Protection Agency (EPA) introduced a uniform Pollution Standard Index (PSI), which was later revised and renamed the Air Quality Index (AQI) in 1999. This standardized scale, with its distinct categories and health advisories, was designed to provide clear, actionable information to the public, empowering individuals to protect their health on days when air pollution levels were elevated, becoming a global model for environmental reporting.

Frequently Asked Questions

What is PM2.5?

PM2.5 refers to fine inhalable particulate matter with a diameter of 2.5 micrometers or less. These microscopic particles are small enough to penetrate deep into the lungs and even enter the bloodstream, posing significant health risks. Common sources include vehicle exhaust, industrial emissions, and wildfires. PM2.5 is a key pollutant tracked by air quality monitoring systems globally due to its direct impact on respiratory and cardiovascular health.

What is the Air Quality Index (AQI)?

The Air Quality Index (AQI) is a color-coded scale used by environmental agencies, like the US EPA, to communicate daily air quality to the public. It converts pollutant concentrations (such as PM2.5, ozone, or carbon monoxide) into a single number that reflects air cleanliness and associated health risks. An AQI of 0-50 is 'Good,' while anything above 100 indicates unhealthy air, providing easy-to-understand guidance for public health protection.

How does PM2.5 concentration relate to AQI?

PM2.5 concentration is directly related to AQI through a linear interpolation formula within specific breakpoint ranges established by environmental agencies. As PM2.5 concentration increases, the corresponding AQI value also rises, moving through categories like 'Good,' 'Moderate,' 'Unhealthy for Sensitive Groups,' and 'Hazardous.' For example, a PM2.5 concentration between 12.1 and 35.4 µg/m³ typically corresponds to an AQI between 51 and 100, categorized as 'Moderate.'

What are the health effects of high PM2.5 levels?

High levels of PM2.5 can cause a range of serious health effects, including respiratory problems like asthma attacks and bronchitis, heart attacks, and strokes. Long-term exposure is linked to decreased lung function, chronic respiratory disease, and premature death. Children, older adults, and individuals with pre-existing heart or lung conditions are particularly vulnerable, prompting public health advisories when AQI levels exceed 100.