CO₂ Level Checker
Enter your CO₂ level and get instant guidance.
CO₂ Level Checker
Type the CO₂ reading from your monitor in parts per million (ppm). The checker explains what that range usually means for an occupied indoor space and what to do next. Guidance follows widely used ventilation benchmarks, not a medical standard.
How to read the result
Outdoor air sits near 420 ppm. Indoors, CO₂ rises as people breathe and falls as fresh air comes in, so the reading is a live indicator of how well ventilation is keeping up with occupancy. The checker groups readings into bands that match widely used ventilation guidance: roughly 800 ppm as well ventilated, 1,000 ppm as the point to act, and 1,500 ppm as poor.
Why the number matters
CO₂ itself is not dangerous at these levels. What matters is what the number implies: when CO₂ is high, anything else people exhale, including respiratory aerosols, is also concentrated, and several studies link readings above about 1,000 to 1,500 ppm with drowsiness and slower decision-making in some people.
Before trusting a high reading
- Check the monitor has been on for at least a few minutes.
- Move it away from your own breath; readings within arm’s reach of a person can be hundreds of ppm high.
- If it reads below 400 ppm indoors, or never drops when a window is opened, calibrate it in fresh air.
Choosing a monitor? See the best CO₂ monitors guide and what a good indoor CO₂ level is.