CO2 Levels Chart: Safe, Normal & Dangerous PPM Ranges
Every CO2 concentration from fresh outdoor air to immediately life-threatening, with the health effects and recommended action at each range. Bookmark this page as a reference, or enter your own reading in the calculator for a personalised interpretation.
Effects: Global average outdoor concentration (2026). Rural air is slightly lower, city streets slightly higher.
What to do: This is the reference point — indoor readings are judged by how far they rise above it.
Effects: Indistinguishable from fresh outdoor air. No measurable effects.
What to do: Nothing to do. Typical of well-ventilated spaces at low occupancy.
Effects: Air still feels fresh. Cognitive performance remains at baseline for virtually everyone.
What to do: The recommended target for homes, offices, and classrooms.
Effects: Some people notice stuffiness. Early, small declines in complex decision-making begin in sensitive individuals.
What to do: Increase ventilation when convenient — open a window or raise HVAC fresh-air supply.
Effects: Measurable declines in focus and decision-making in controlled studies. Drowsiness in meetings, poorer sleep quality.
What to do: Ventilate now. This is the range most occupied bedrooms and meeting rooms reach.
Effects: Headaches, fatigue, and difficulty concentrating are common with sustained exposure.
What to do: Open windows or doors immediately; reduce occupancy; check that HVAC is not recirculating only.
Effects: Pronounced drowsiness, headaches, and impaired judgment. 5,000 ppm is the 8-hour occupational exposure limit (OSHA PEL).
What to do: Do not spend extended time here. Fix the ventilation problem before reoccupying.
Effects: Rapid breathing, elevated heart rate, nausea, and disorientation as levels climb. Only reached in sealed or industrial settings.
What to do: Leave the space. Levels like this indicate a serious source (dry ice, fermentation, industrial leak).
Effects: IDLH (Immediately Dangerous to Life or Health). Loss of consciousness within minutes; asphyxiation risk.
What to do: Evacuate immediately. Emergency ventilation and breathing apparatus territory.
How to Read This Chart
There are two different questions hiding in “is this CO2 level safe?” — acute toxicity and air quality. Acutely, CO2 only becomes hazardous above 5,000 ppm, levels almost never seen in homes. But as an air-quality signal, CO2 matters from 800 ppm upward: it tracks how much exhaled air you are rebreathing, and with it airborne pathogens, odours, and the documented cognitive effects of stale air.
Typical Readings in Real Spaces
- Outdoor air: ~420 ppm
- Well-ventilated living room: 500–700 ppm
- Office at full occupancy: 800–1,200 ppm
- Closed bedroom by morning: 1,500–2,500 ppm (why this ruins sleep)
- Crowded classroom: 1,200–3,000 ppm (school monitoring guide)
- Car with 2+ people on recirculate: 2,500–4,000+ ppm (CO2 in cars)
Measuring Accurately
These numbers are only as good as your sensor. Choose a monitor with a true NDIR or photoacoustic sensor (not an “eCO2” estimate), place it correctly, and calibrate it occasionally. Our picks: best for home, best under $100, and the full monitor directory.
Frequently Asked Questions
What CO2 level is dangerous for humans?+
Acute danger begins around 5,000 ppm, the 8-hour occupational exposure limit; 40,000 ppm is immediately dangerous to life. However, chronic exposure above 1,000-1,500 ppm — common in bedrooms and offices — measurably impairs focus, sleep, and wellbeing long before acute toxicity.
What is a normal CO2 level indoors?+
Occupied indoor spaces typically run 600-1,200 ppm. Below 800 ppm indicates good ventilation. Closed bedrooms routinely reach 1,500-2,500 ppm overnight, and crowded rooms can exceed 2,000 ppm within an hour.
What CO2 level should I aim for at home?+
Keep living spaces below 800 ppm and bedrooms below 1,000 ppm overnight. These targets keep air feeling fresh and avoid the cognitive and sleep effects documented above 1,000 ppm.
Why is outdoor CO2 420 ppm and not zero?+
CO2 is a natural component of the atmosphere. Pre-industrial levels were about 280 ppm; fossil fuel emissions have raised the global average to roughly 420 ppm as of 2026, rising 2-3 ppm per year. Indoor levels can never be lower than the outdoor air used to ventilate.