Understand CO₂ & get the most out of your monitor

Drag the slider to explore different CO₂ levels, tap real‑world scenarios to see typical readings, learn how NDIR sensors measure CO₂, and follow our simple steps to set up and calibrate your KnowCO₂.

CO₂ ppm explorer

800

ppm CO₂

Good indoor air

Common target range for comfortable, ventilated indoor spaces.

Keep doing what you’re doing. If it rises, add fresh air.

Tap a scenario to set the slider:

Bedroom overnight

People exhale CO₂; closed rooms climb overnight.

Office meeting

Small room + many people = CO₂ rises quickly.

Classroom

Aim for lower is better with reasonable comfort.

Car with windows up

CO₂ spikes fast—crack a window or use fresh‑air mode.

Outdoor air today is typically in the 420–430 ppm range (varies by season and location). NOAA’s Mauna Loa daily average on 30 Jan 2026 was around 428 ppm.

How NDIR sensing works

High‑quality CO₂ monitors like KnowCO₂ use non‑dispersive infrared (NDIR) technology. Infrared light passes through a small gas chamber, a filter focuses on a wavelength that CO₂ absorbs strongly (around 4.26 µm), and a detector measures how much light remains. More CO₂ means more absorption and less detected light.

Absorbed 20%

Detected 80%

This simplified graphic updates as you adjust the ppm slider above. Real sensors add temperature compensation, optics and signal processing, but the basic principle stays the same.

Quick start & baseline calibration

Follow these three simple steps to ensure your KnowCO₂ readings are accurate.

Give it fresh air. With the device powered on, place it outdoors for a few minutes. If you can’t go outside, put it near an open window or door where outdoor air can reach it.

Put it where it matters. Bring the monitor back to the room or area you want to measure—bedroom, office, classroom, workshop or car.

Let it run continuously. If connected to Wi‑Fi or the cloud, it will keep sending data. For best results, the device should occasionally see fresher air (doors opening, windows cracked or normal ventilation cycles). Automatic Self‑Calibration needs this exposure to maintain a correct baseline.

Baseline note: Global outdoor CO₂ in 2026 hovers around 420–430 ppm and slowly increases every year. This serves as a reference for calibration. The monitor uses this when it is exposed to fresh air.

Automatic Self‑Calibration (ASC)

ASC keeps your sensor accurate over long periods by slowly adjusting its baseline. It assumes that at least once per week the monitor sees clean outdoor air (~400 ppm) and uses the lowest reading it encounters as the reference.

Leave the monitor running continuously for several days for the first calibration.
The first ASC adjustment typically happens after 2 days; full convergence takes about 7–9 days.
ASC may not work properly in sealed or continuously occupied spaces—give it fresh air occasionally.

If in doubt, do nothing. ASC operates quietly in the background and keeps adjusting over time. Manual recalibration is available on the Calibration page.

Get your KnowCO₂ monitor