CO2 measurement range in ppm or percent CO2 - Which is right for you?

What range of CO2 measurement is best for your application?

Carbon dioxide sensors and measurement devices are offered in many different ranges, from 1,000ppm (parts per million) to 100% CO2. Selecting the sensor or device with the correct range of CO2 to be measured for your application is important. This is because, in general, the narrower the range of CO2 levels that is measured, the more accurate the sensor or device will be.

CO2 sensors can be divided into 3 groups:

  • 1% CO2 for indoor (or outdoor) air quality
  • 5% CO2 for personal safety
  • 10-100% CO2 for industrial or biological applications

Selecting the proper CO2 range for your application makes it easier to choose from our wide range of available CO2 sensors and products. However, first it's important to know the difference between parts-per-million and % CO2.

PPM vs. % CO2


Carbon dioxide is considered a trace gas in the atmosphere. Suppose you had a box of dry air with 1 million molecules of gas in it. If you could count the molecules, here's what you'd find:

  • 780,840 molecules of nitrogen (78.08%)
  • 209,460 molecules of oxygen (20.9%)
  • 93,400 molecules of argon (0.93%)
  • 400 molecules of carbon dioxide
  • A few molecules of hydrogen, helium, methane, etc.

As you can see, once you get past counting the number of molecules of nitrogen, oxygen and argon, the number of  molecules of the remaining gases in our theoretical box of air is very small. For this reason, instead of talking about percentage of molecules, scientists talk about Parts-Per-Million. So 0.0400% CO2 is equal to 400 parts-per-million, which is commonly abbreviated 400ppm.

Indoor/Outdoor Air Quality

When talking about indoor or outdoor air, parts-per-million makes sense. Only in rare instances like being in a cave or near an exploding volcano would you ever be exposed to CO2 levels above 1% (10,000ppm) in nature.

That's why for indoor air quality (IAQ) or climate science applications, a 2,000ppm to 10,000ppm CO2 sensor or monitor is the right choice. Fresh air contains approximately 400ppm CO2. The ASHRAE Standard for ambient indoor air in occupied spaces is less than 1,000ppm. Therefore, an indoor air quality monitor or transmitter with a sensor that measures at these levels of CO2 will work best for indoor applications.

The most popular sensors we sell in this range are the K30 CO2 Sensor by Senseair and the COZIR Ambient CO2 sensor. Our most popular product is the TIM10 Indoor Air Quality monitor.

A 10,000ppm CO2 sensor is a good choice for air quality applications near car parks or garages that must meet OSHA specifications. OSHA requires that the time-weighted average (TWA) over an 8-hour workday should not exceed 5,000ppm.

Personal Safety

For CO2 safety applications where workers or the public are around stored carbon dioxide, a 0-5% CO2 sensor or device is a good choice. These sensors can be used to set off an alarm in the case of a carbon dioxide leak that can be potentially harmful. For example, the COZIR GC-0015 0-5% CO2 sensor would be a good choice for this type of application. In addition, all our RAD CO2 Storage Safety alarms and personal CO2 alarms use a 5% CO2 sensor.

Industrial and Biological Processes

For industrial and biological processes like wood gasification or biological incubators, a 20-30% CO2 sensor or device is a good solution. For example, our SenseAir K33 ICB or COZIR Wide-Range 20% sensors are in this range. In addition, the high-speed SprintIR6S 20% CO2 sensor is an excellent choice for capnography.

For applications like controlled atmosphere storage for grains that require the ability to measure up to 100% CO2, we recommend the COZIR GC-0016 and SprintIR GC-0018 CO2 sensors.

With all the different sensors and products we offer, it might seem confusing as to which one is best for your particular application. If you have questions, call or email us our sales engineers. They will be happy help you make the right selection.


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