The dead space in the respiratory system refers to the part of the respiratory tract where no gas exchange occurs, such as the trachea and bronchi.
In an average adult, the tidal volume (air inhaled per breath) is about 500 ml .
Out of this, roughly 150 ml remains in the dead space (conducting zone), while about 350 ml reaches the alveoli for actual gas exchange.
So, the volume of air filled in dead space is approximately .

──────────────────────────────────────────────────────────────────────────────────────────