Want to know how good the air in your home actually is? By measuring indoor air quality you get concrete values to work with instead of guessing. Here is what you can measure and how to do it.
Short answer: You measure indoor air quality with an air quality monitor that shows values such as particles (PM2.5), carbon dioxide (CO2), volatile organic compounds (VOC) and relative humidity. Together they give a picture of how clean and fresh the air is and when it is time to air out.
What does indoor air quality mean?
Indoor air quality is about how clean the air is and how well it is exchanged. Several factors matter at the same time: the amount of small particles, the level of carbon dioxide, the presence of gases and vapours, and the humidity. No single number tells the whole story; it is the combination that counts.
Which values should you measure?
The most common values an air quality monitor shows are these:
| Value | What it describes | Rough guideline |
|---|---|---|
| PM2.5 | Small particles in the air | As low as possible |
| CO2 (carbon dioxide) | How well the air is exchanged | Below about 1000 ppm |
| TVOC | Volatile organic compounds and vapours | As low as possible |
| Relative humidity | The moisture level in the air | 30 to 60 percent |
High carbon dioxide levels are often the first sign that a room needs airing, because the air then feels stuffy.
How to measure indoor air quality step by step
- Get an air quality monitor that shows the values you care about. Some measure only particles or carbon dioxide, others several values at once.
- Place the monitor in a room you spend a lot of time in, at roughly face height and not right next to a window or door.
- Read it over time. The values change with cooking, cleaning and how many people are in the room, so follow them over a few days for a fair picture.
Common sources of poorer indoor air
Indoor air is affected both by what we do and by what is in the home. Knowing the most common sources makes it easier to interpret the readings:
- Cooking and candles that release particles.
- Dust and textiles that stir up small particles as we move around.
- New furniture, rugs and building materials that can release volatile organic compounds (VOC) for a while.
- Too little airing, which lets carbon dioxide and moisture build up.
Many of the sources can be influenced, either by reducing them or by airing and cleaning the air more often.
What do you do if the values are poor?
The action depends on which value stands out:
- High carbon dioxide: air out and review the ventilation so the air is exchanged more often.
- Lots of particles: reduce the sources, dust and vacuum regularly. An air purifier captures particles such as dust and smoke in the air.
- Wrong humidity: if it is outside 30 to 60 percent you may need to adjust it, for example with a dehumidifier if it is too humid.
If you want to read more, see our guides on improving air quality at home, how to think about the air in the bedroom and how to choose a quiet air purifier.
Frequently asked questions
How do you measure indoor air quality?
With an air quality monitor that shows values such as particles (PM2.5), carbon dioxide (CO2), volatile organic compounds (VOC) and relative humidity. Place it in a room you use a lot and read it over time.
What is a good indoor CO2 level?
Below about 1000 ppm is generally considered good. If carbon dioxide rises well above that the air often feels stuffy, and it is time to air out or improve ventilation.
What is PM2.5?
PM2.5 is very small particles in the air, smaller than 2.5 micrometres. The lower the value the cleaner the air. Particles come from cooking, candles, smoke and dust, among other things.
Do you need an air quality monitor?
No, but it gives concrete values instead of guesses and makes it easier to know when you need to air out, clean or purify the air.
