The Confidence Score

The Confidence Score

The Confidence Score is a numerical value displayed on the PurpleAir map ranging from 0 to 100 percent. Every sensor that contains two channels—the PurpleAir Classic, Classic SD, Flex, and Zen—has an assigned Confidence Score. PurpleAir Models that contain one channel—the Indoor and Touch—do not have a Confidence Score. This is because the Confidence Score is calculated by using readings from both channels and comparing them. Sensors with one channel do not have two readings to compare, so they can’t have a confidence score.

The Confidence Score is a measure of how confident PurpleAir is in the readings a sensor is reporting. That is, it reflects PurpleAir’s belief about the reliability and credibility of a sensor’s data. A higher confidence score indicates a greater level of confidence in the accuracy of the sensor’s data, while a lower score suggests a lower degree of confidence.

PM2.5 data is omitted from affecting the confidence score if it results in a US EPA PM2.5 AQI above 2,000

Sensor Opacity

It is possible that while viewing the map, you might see a sensor that has a lowered opacity. In other words, it’s a little bit see-through. This is correlated with the sensor’s confidence score. After confidence drops past a certain point, that sensor’s dot on the map will have a lowered opacity. Indoor sensors—those with only one laser counter— will always have a lowered opacity on the map because we can never be 100% confident in their readings. See image below:


Channel Indicators

You may also see on the map that your sensor has a downgraded channel. There are two ways that this can happen. First, the system detected that one of the channels in your device was outputting erroneous readings, and it automatically downgraded the channel. Second, a PurpleAir staff member determined that your sensor was outputting erroneous readings and manually downgraded a channel.


Downgrades directly affect a sensor’s confidence score. A sensor with one downgraded channel will appear see-through, as seen above. A sensor that has had both channels downgraded will appear as though it is offline––it will be grayed out on the map.

Channel Output Deviation

PurpleAir sensors, and the laser counters within them, are not perfect. The two channels inside a device will not always track strictly with each other. Sometimes, this deviation can be due to an issue with the sensor or its readings. However, this is not always the case. There is an accepted Maximum Consistency Error. According to the laser counter manufacturer, Plantower, the accepted range for both PMS5003 and PMS6003 laser counters is as follows:

  • ±10μg/m³ @ 0~100 μg/m³
  • ±10% @ 100~500 μg/m³

Please note, these ranges are for raw PM2.5 readings, and not AQI levels.



Learn More

PurpleAir Map Guide
View Your Sensor on the Map
Why Should I Put my Indoor Sensor on the Map

Is it possible to see the calculation/math that is used to provide the confidence score for each channel? I’m very curious on how it is calculated.