There’s no single universal scale, but most monitors map to the US Air Quality Index, where 0–50 is “good” and 51–100 is “moderate.” Devices with a 0–100 proprietary score treat higher as better, with green usually meaning low particulates, low VOCs, and CO2 under roughly 800–1,000 ppm. Aim for the green band.
What does an indoor air quality monitor's score measure?
A combined indoor air quality score usually blends several readings into one figure. The score is only as meaningful as the sensors behind it, so it is worth checking which pollutants a given air quality monitor actually tracks before trusting the number.
Because there is no legally standardized indoor score the way there is for outdoor AQI, two monitors can report the same room differently. Treating the number as a trend — is it improving after you ventilate — is more useful than chasing one specific figure.
Brands including Airthings, Temtop, IQAir, and Awair each calculate their composite score with a somewhat different weighting, which is another reason a score of 80 on one device is not directly comparable to an 80 on another.
PM2.5, particulate matter, and VOC
PM2.5 measures the smallest, most concerning fraction of particulate matter, the fine dust and smoke that can reach deep into the lungs. VOC readings track gases off-gassed by paint, furniture, and cleaning products, a completely separate pollutant category from particles. A room can score well on particulate matter while still reading high on VOCs, so both figures deserve a look, not just the composite number.
CO2 and formaldehyde readings
CO2 tracks how well a room is ventilated, since it climbs steadily whenever people breathe in a closed space. Formaldehyde is a specific VOC that some monitors, including models from Airthings and IQAir, track separately because of its common presence in new furniture and flooring. A newly renovated or newly furnished room is where a dedicated formaldehyde reading is most worth having.
What counts as a good reading on the AQI scale?
Broadly: PM2.5 in the low single digits to low double digits in micrograms per cubic meter, CO2 under about 800 to 1,000 ppm, and VOCs in the device's low or green zone. When all sit in their healthy bands on the AQI-style scale, the composite score reads good.
These sub-readings matter more than the headline number because they tell you what to fix. A good particulate reading but high CO2 points to ventilation; low CO2 but high VOCs points to a source like new furnishings off-gassing into the room.
Humidity, temperature, and healthy ranges
Humidity between 30 and 50 percent and a comfortable temperature both factor into some monitors' overall health score, since both extremes encourage mold, dust mites, or general discomfort. A monitor that tracks only particulates misses this half of the indoor climate picture. Temperature swings alone rarely count against the score, but paired with high humidity they push comfort and mold risk in the wrong direction together.
How does sensor accuracy affect calibration needs?
Consumer-grade sensor accuracy varies by brand and by pollutant. Temtop and Awair both publish accuracy specs for their CO2 and PM2.5 sensors, and most units benefit from periodic calibration to correct for slow drift over months of use.
A monitor left in one spot for a long stretch, especially in a room that never fully airs out, is more prone to calibration drift than one in a well-ventilated space. A lower-accuracy sensor is still useful for spotting trends, even if the exact number is off by a small margin from a lab-grade instrument.
Real-time data logging and alerts
Real-time readings update every few seconds, while data logging stores a history you can review for trends over days or weeks. Alerts push a notification the moment a pollutant crosses your chosen threshold, which is more useful than checking the score manually.
App control and connectivity
Most monitors pair with an app that shows the real-time score, the data logging history, and lets you configure alerts. The EPA's own indoor air resources note that continuous monitoring, not a single spot check, is what actually helps you manage a room's air quality over time.
Should you trust the single score?
Use it as a quick daily glance, but look at the component readings before acting. A single blended score can hide a problem in one pollutant while the others look fine. The value of a monitor is showing what changes when you ventilate, filter, or remove a source.
Comparing two rooms, or the same room morning versus evening, tells you far more than memorizing what counts as a universally good indoor air quality score.