Air quality is a vital aspect of public health. The clearer and cleaner the air we breathe, the lower the risk of respiratory illness, cardiovascular problems, and general discomfort. Governments across the globe track airborne pollutants and report an Air Quality Index—commonly called the AQI—to help people quickly gauge whether it is safe to work, exercise, or spend time outdoors. Although the concept seems straightforward, calculating the AQI involves a series of standardized steps, including pollutant measurement, breakpoints, and index scaling. This tool offers a concise way to compute the AQI from particulate matter values, giving you a snapshot of environmental conditions in your area.

The most common pollutants that influence air quality are fine particles (PM2.5), larger particles (PM10), ground-level ozone, nitrogen dioxide, sulfur dioxide, and carbon monoxide. For simplicity, this calculator focuses on PM2.5 and PM10 because these tiny particles often drive overall index values. PM2.5 particles are less than 2.5 micrometers in diameter—about 1/30th the width of a human hair. They originate from combustion sources like vehicle exhaust, wildfires, and certain industrial processes. Due to their small size, they can penetrate deep into the lungs and even enter the bloodstream, making them particularly dangerous for people with asthma or heart conditions. PM10 particles are larger but still small enough to be inhaled and can cause irritation in the nose and throat.

In the United States, the Environmental Protection Agency established breakpoints that map concentration ranges of each pollutant to an index scale from 0 to 500. A lower index indicates cleaner air, while higher values signal more severe pollution. For instance, a PM2.5 concentration between 0 and 12 µg/m³ corresponds to an AQI range of 0 to 50, labeled “Good.” When concentrations rise to around 35 µg/m³, the AQI jumps into the “Moderate” or even “Unhealthy for Sensitive Groups” category. These breakpoints are based on epidemiological studies linking pollutant exposure to health outcomes, ensuring that the index has real-world relevance.

To compute the AQI, we take a pollutant’s measured concentration and locate the two breakpoints surrounding it. For example, if PM2.5 is 25 µg/m³, it falls between the 12.1–35.4 µg/m³ range, which maps to an AQI of 51–100. A linear equation converts the concentration within that range to a specific index value. This procedure is repeated for PM10 or any other pollutant, resulting in several sub-indices. The highest sub-index becomes the overall AQI because health advisories are driven by the most hazardous pollutant at the time.

This calculator follows that method in a simplified form. After entering your PM2.5 and PM10 concentrations, it checks each against the official breakpoints. It then calculates the sub-index for each pollutant and chooses the larger value. The interface also displays a qualitative category such as “Good,” “Moderate,” or “Unhealthy.” All calculations happen instantly within your browser, so no data is stored or transmitted. You can experiment by adjusting the values to see how small increases in pollution can push the index from one category to the next.

Understanding AQI categories can influence daily decisions. When the index is below 50, outdoor activities pose minimal health risks to the general population. As the AQI climbs above 100, individuals with respiratory conditions or heart problems may begin to experience symptoms such as coughing or shortness of breath. At 150 or higher, even healthy individuals can feel the effects of poor air quality. Long-term exposure to high particulate levels has been linked to increased rates of asthma, reduced lung function in children, and heightened mortality. By checking the AQI, you can decide whether to limit time outside, close windows, or use air filtration indoors.

Pollution levels fluctuate due to weather, traffic patterns, and local industry. For example, temperature inversions can trap pollutants near the ground, spiking the index. Wildfire smoke can travel hundreds of miles, turning a previously clean day into a hazardous one. Conversely, strong winds or rainfall can disperse particles and improve air quality. Because conditions change quickly, many communities update the AQI hourly. Websites and smartphone apps provide real-time data, but this calculator allows you to perform your own estimations if you know the pollutant concentrations from a monitoring station or sensor.

Beyond individual health, the Air Quality Index has broader societal significance. High AQI days can lead to school closures, restrictions on industrial activity, and even driving bans in some cities. Government agencies issue advisories urging residents to stay indoors or limit strenuous exercise. If you suffer from allergies or other sensitivities, tracking the AQI can help you plan trips, workouts, or outdoor events when the air is clearer. Some people also use the AQI to decide whether to wear protective masks, especially in regions prone to smoke or dust storms.

This calculator’s code is intentionally concise to keep it accessible and efficient. The breakpoint arrays cover common AQI ranges, and the `calcSubIndex` function performs the core linear interpolation. While it only handles PM2.5 and PM10, the same approach can extend to ozone or other pollutants by adding more breakpoint sets. Because everything is client-side, you can modify the source as needed to suit your region’s specific regulations or convert the formula to different units. In any case, the goal is to demystify the AQI process so you understand how official numbers are derived.

Whether you are an athlete monitoring smog before a run, a parent concerned about children playing outside, or a city planner assessing pollution trends, a quick AQI calculation is a powerful tool. By translating raw particulate concentrations into a familiar scale, it provides immediate context for environmental conditions. Bookmark this page, try it out with local data, and share it with friends and family so everyone can make informed decisions about the air they breathe.