CO₂ Breathing Emission Calculator

Yes. With every breath, your body exhales CO₂ as a byproduct of metabolism — the process of converting oxygen and glucose into energy. The air you exhale contains roughly 4–5% CO₂, which is about 100 times more concentrated than the outdoor air you inhale (around 0.04%). In a closed space with multiple people, this quickly adds up.

At normal outdoor levels (~420 ppm) CO₂ is harmless. As indoor concentrations rise, symptoms begin to appear: above 1,000 ppm many people feel drowsy and find it harder to concentrate; above 2,000 ppm headaches and reduced cognitive performance are common; levels above 5,000 ppm can cause nausea, increased heart rate, and blood pressure changes; and concentrations above 40,000 ppm are immediately life-threatening. The good news is that proper ventilation keeps indoor levels well below harmful thresholds.

Most health guidelines classify indoor air as acceptable below 1,000 ppm. Between 1,000–2,000 ppm, occupants may experience complaints and decreased productivity. Above 5,000 ppm is the OSHA permissible exposure limit for an 8-hour workday. Acute toxicity starts around 40,000 ppm. For reference, a poorly ventilated classroom full of students can easily reach 2,000–3,000 ppm.

Ventilation dilutes and removes CO₂-laden air, replacing it with fresher outdoor air. Air changes per hour (ACH) measures how many times per hour the entire room volume is exchanged. A typical home might have 0.5–1.5 ACH, while well-ventilated offices target 4–6 ACH. Even a small increase in ACH — like opening a window — can dramatically reduce CO₂ build-up, especially in smaller rooms with multiple occupants.

Plants absorb CO₂ during photosynthesis (6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂), using it to build sugars and releasing oxygen. However, the rate at which typical houseplants absorb CO₂ is far too slow to meaningfully reduce concentrations in an occupied room. You would need hundreds of plants to offset even one person's exhalation. Proper mechanical or natural ventilation remains the most effective solution.

The most effective strategies are: (1) Increase ventilation by opening windows or doors; (2) Use mechanical ventilation systems or HVAC with fresh air intake; (3) Reduce occupancy or take regular breaks outdoors; (4) Install CO₂ sensors to monitor levels in real time; (5) Choose larger rooms for group activities. Even a short airing out of 5–10 minutes can reduce CO₂ levels significantly.

Human breathing is the dominant source of elevated indoor CO₂. Additional sources include combustion appliances (gas stoves, heaters, fireplaces), burning candles, and even pets. Outdoor CO₂ (currently ~420 ppm globally) sets the baseline that infiltrates through walls and gaps. In well-occupied rooms without ventilation, human exhalation is overwhelmingly the main driver of CO₂ build-up.

This calculator uses a steady-state mass balance model based on established CO₂ generation rates per MET level, room volume, and ventilation rate. It provides a reasonable estimate for typical conditions. Real-world CO₂ levels can vary due to factors like room leakage, uneven air mixing, variation in individual metabolism, and fluctuating occupancy. For precise measurements, use a calibrated CO₂ sensor.