At standard temperature and pressure 1 kg of CO2 has a volume of around 500 l. Exhaled air contains about 4% CO2, so you would have to exhale 12500 l of air to

At standard temperature and pressure 1 kg of CO2 has a volume of around 500 l. Exhaled air contains about 4% CO2, so you would have to exhale 12500 l of air to put out 500 l of CO2. At 0.5 l per exhalation that's 25,000 breaths, which seems rather on the high side: 17 breaths per minute, round the clock. It seems like a bit of a high estimate; could be true for people who are very physically active during parts of every 24 h period.