How to Read the Numbers on an Air Quality Monitor

On this page (9 sections)

1. Which numbers should you read first?
2. How do you read a PM2.5 number?
3. What does a CO2 reading tell you?
4. How should you interpret VOC or TVOC readings?
5. What do humidity and temperature readings mean?
6. Should you trust a color or overall air quality score?
7. How can you compare readings from day to day?
8. What should you do when a number changes?
9. How to read air quality monitor numbers in practice

To read an air quality monitor, check each measurement on its own, then watch how it changes over time. PM2.5, CO2, VOCs, humidity, and temperature describe different conditions, so one number can't sum up your whole home.

Start with the label and unit beside each reading. A percentage, ppm, and µg/m³ measure different things, and the monitor's color or overall score may combine several measurements into one summary.

Which numbers should you read first?

Start with the measurements your monitor actually tracks: particles, gases, humidity, and temperature. The names and units tell you what each sensor is reporting.

• PM2.5 means fine particles 2.5 micrometers wide or smaller. Many monitors show a concentration in micrograms per cubic meter (µg/m³).
• PM10 counts larger airborne particles as well as smaller ones. Some monitors show both PM2.5 and PM10.
• CO2 means carbon dioxide, often displayed in parts per million (ppm). It can help you notice when a room may need more fresh air.
• VOCs or TVOC refer to volatile organic compounds or a combined estimate of them. Monitors may use an index or concentration, and results can depend on the sensor.
• Humidity is usually shown as relative humidity (RH), a percentage.
• Temperature is shown in degrees, usually Fahrenheit or Celsius.

A monitor may not measure every item on this list. For example, CO2 is not carbon monoxide, and a particle sensor doesn't identify a specific pollutant.

For a closer look at the particle reading, see what PM2.5 means on an air quality monitor and how PM2.5 differs from PM10.

How do you read a PM2.5 number?

Read PM2.5 as a particle concentration, then compare it with the same monitor's past readings. A sudden rise can help you spot a change in the room, but it won't identify what caused it.

Cooking, candles, smoke, and dusty activity can affect fine particle levels. Note what was happening when the number changed, and see whether it falls after the source stops or ventilation changes.

The Awair Element tracks PM2.5 along with temperature, humidity, CO2, and VOCs. Its app provides real-time information and tracks changes over time.

Don't treat one brief reading as a diagnosis or a complete picture of exposure. If you want a deeper explanation of the particle category, read what PM2.5 means on a monitor.

What does a CO2 reading tell you?

A CO2 reading can show how carbon dioxide changes as people use a room and fresh air moves through it. It is not a direct measure of every pollutant or a carbon monoxide alarm.

Compare readings in the same room under similar conditions, such as with a similar number of people and similar window or door positions. A gradual rise during occupancy may be a cue to improve ventilation, then check whether the number changes afterward.

The Amazon Smart Air Quality Monitor tracks carbon monoxide (CO), not CO2, alongside PM2.5, VOCs, humidity, and temperature. Its color-coded light and Alexa app provide an air quality indication and score, but don't confuse a CO alert with a CO2 ventilation reading.

For more on interpreting carbon dioxide, see what counts as a good CO2 reading. Check your device's sensor list before using it to answer a question about a gas.

How should you interpret VOC or TVOC readings?

Treat a VOC or TVOC number as a sensor's broad indication, not a reading for one named chemical. The display may use an index or a concentration, so check its unit and the maker's explanation.

Cleaning products, cooking, and other household activities can change VOC readings. Note the timing and see whether the value moves when the activity ends or the room is aired out.

The AprilAire Smart Air Quality Monitor measures VOCs and TVOC, plus CO2, PM2.5, humidity, and temperature. Its Healthy Air App provides explanations, trends, and notifications.

A VOC reading does not tell you which compound is present or whether a specific health limit has been exceeded. Use it to notice patterns, and follow product instructions or qualified guidance when you need to identify a particular substance.

What do humidity and temperature readings mean?

Humidity is the amount of moisture in the air, shown as relative humidity, while temperature shows how warm or cool the room is. These readings help describe comfort conditions, but they don't measure particles or gases.

Read both values in the room where you spend time, and compare them across the day. Sunlight, heating, cooking, showers, and humidifiers can shift them.

The Qingping Air Quality Monitor Gen 2 displays temperature, humidity, CO2, PM2.5, PM10, eTVOC, and noise. It also supports historical data in its app, which can help you compare readings over time.

If humidity is your main concern, use our guide to good indoor humidity levels to understand that measurement separately. A temperature or humidity reading cannot confirm whether the air is clean.

Should you trust a color or overall air quality score?

Use a color or combined score as a quick summary, then check the individual readings behind it. Different monitors may combine measurements in different ways, so similar colors don't guarantee that two devices use the same scale.

An overall score can be useful for noticing a change at a glance. Open the app or display details to see whether particles, gases, or comfort measurements shifted.

Our plain guide to home air quality monitor readings explains the common measurements and how monitors present them. To understand sensor limits and variation, see how accurate home air quality monitors are.

How can you compare readings from day to day?

Keep the monitor in one suitable place and compare readings under similar conditions. Moving it between rooms or setting it beside a window, vent, or cooking area can change what it detects.

Use a simple note of the room, time, occupancy, and recent activities when a reading surprises you. Look for repeated patterns rather than reacting to every brief spike.

A monitor may refresh measurements at different rates, and some readings respond faster than others. Follow its instructions for placement and allow time after moving it before comparing results.

What should you do when a number changes?

Check the measurement, its unit, and what was happening nearby before taking action. If a reading stays unusual, check the monitor's guidance and consider the room's ventilation or likely sources.

For particles, consider recent cooking, smoke, or dust. For CO2, consider how many people are in the room and whether fresh air is entering; for VOCs, think about recent cleaning or cooking.

A monitor can point to a pattern, but it may not identify the source or confirm a hazard. Use the right dedicated detector for safety concerns, and follow local or professional guidance when needed.

How to read air quality monitor numbers in practice

To read air quality monitor numbers, match each value to its sensor and unit, then compare it with the room's pattern over time. Use PM2.5 for fine particle changes, CO2 for a ventilation clue, VOC or TVOC for broad trends, and humidity and temperature for comfort conditions.

Choose a monitor based on the measurements you need: the Awair Element covers PM2.5, CO2, VOCs, humidity, and temperature; the Amazon monitor includes CO and omits CO2; AprilAire adds TVOC; Qingping also shows PM10 and noise. For the next step, read how air quality monitors work.

Frequently asked questions

What do the numbers on an air quality monitor mean?

Each number describes a different measurement, such as particle levels, carbon dioxide, volatile organic compounds, humidity, or temperature. Check the unit and the monitor's guide for each reading, then compare changes over time.

A color or combined score is a summary, not a replacement for the individual measurements.

What does PM2.5 mean on an air quality monitor?

PM2.5 refers to fine particles that are 2.5 micrometers wide or smaller. Monitors often show this as a concentration in micrograms per cubic meter (µg/m³).

A rising reading can prompt you to look for smoke, cooking, candles, or other particle sources, but it doesn't identify the source by itself.

Is a high CO2 reading the same as carbon monoxide?

No. Carbon dioxide (CO2) and carbon monoxide (CO) are different gases and need different sensors.

A CO2 reading often helps you judge how fresh the air is in an occupied room; it does not detect carbon monoxide unless the monitor specifically includes a CO sensor.

Why does my air quality monitor show different readings in different rooms?

Rooms have different sources, ventilation, occupancy, and airflow, so measurements can vary. The monitor's location also matters: keep it in the room you want to understand and follow its placement instructions.

Compare readings under similar conditions before deciding that one room consistently has a problem.