CO2 from Breathing Calculator

Human CO2 production results from cellular respiration, the metabolic process that converts glucose and oxygen into energy, water, and carbon dioxide. The simplified equation is: C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy (ATP). Every cell in the body performs this reaction continuously. At rest, an average adult breathes about 12-20 times per minute, inhaling about 500 mL of air per breath (tidal volume). Inhaled air contains about 0.04% CO2 (400 ppm), while exhaled air contains about 4% CO2 (40,000 ppm), a 100-fold increase. This means each breath adds about 20 mL of CO2 to the exhaled air. The basal metabolic rate (BMR) determines resting CO2 production. Larger individuals have higher BMRs and produce more CO2. The relationship is approximately proportional to body weight, with adjustments for body composition (muscle produces more CO2 than fat at rest). During exercise, CO2 production increases dramatically. Moderate exercise (jogging) increases metabolic rate by 4-6 times, and intense exercise (sprinting) by 10-15 times. Breathing rate, tidal volume, and CO2 concentration in exhaled air all increase to expel the additional CO2. An important ecological context: human respiratory CO2 is carbon-neutral. The carbon in exhaled CO2 was recently captured from the atmosphere by the plants and animals we eat. This is fundamentally different from fossil fuel CO2, which releases carbon that was sequestered underground millions of years ago, adding new carbon to the active cycle. The average person produces about 300-400 kg of CO2 per year from breathing alone. For comparison, the average American's total carbon footprint is about 16,000 kg (16 tonnes) of CO2 equivalent per year, meaning breathing accounts for only about 2-3% of personal emissions. Transportation, electricity, food production, and goods manufacturing dominate the carbon footprint. Indoor CO2 levels rise when occupied rooms are poorly ventilated. Normal outdoor air is about 420 ppm CO2. Well-ventilated rooms maintain 600-800 ppm. Poorly ventilated rooms can reach 1,000-2,500 ppm, causing drowsiness and reduced cognitive function. This is why ventilation standards specify minimum fresh air delivery rates per occupant.