How much oxygen do we exhale after use?

When we breathe in, the air we inhale contains approximately 21% oxygen. During the process of respiration, our bodies utilize a significant portion of that oxygen for metabolic processes. By the time we exhale, the composition of the air changes considerably.

After that metabolic use, the oxygen concentration in the exhaled air drops to around 16%. This indicates that our bodies have consumed about 5% of the oxygen originally present in the inhaled air, which is consistent with human respiratory physiology. Thus, the correct understanding of oxygen usage in our respiratory system makes 16% the accurate measurement for how much oxygen we typically exhale after use.