🫁 CO2 Breathing Emission Calculator
Estimate how much CO2 a person (or a group of people) exhales through normal breathing over a day or year.
What this calculator does
This tool estimates the amount of carbon dioxide exhaled through normal human breathing (respiration), based on how many people are involved, their activity level, and how many hours they spend at that activity level each day.
How the estimate is calculated
The rate of CO2 exhaled depends heavily on metabolic rate and breathing rate. Widely cited physiology references put resting/sleeping exhalation at roughly 17 grams of CO2 per hour, light activity (sitting or gentle walking) at about 35 grams per hour, moderate activity at about 65 grams per hour, and vigorous exercise at around 150 grams per hour or more, since faster breathing and higher oxygen consumption both increase CO2 output. The calculator multiplies the applicable hourly rate by your stated hours and headcount, then scales to a full year.
Note that human respiration is part of the natural short-term carbon cycle — the CO2 exhaled comes from food recently grown from atmospheric carbon, unlike fossil fuel combustion which releases long-buried carbon. This calculator is intended purely for educational curiosity about respiration rates, not as a measure of a person’s net carbon footprint.
- For general educational and planning purposes only; individual metabolic rates vary by age, size, and health.
- This is not medical or physiological diagnostic information.