Pressure at sea level is taken as 76 cm of MERCURY column which is one atmosphere. But his pressure varies with altitude as the density of air decreases as we rise up and the air becomes rarer. For every 105 m rise in height, pressure decreases by 1 cm of the mercury column.
![](https://www.sarthaks.com/?qa=blob&qa_blobid=5257987069035144594)
Graph shows the approximate variation of pressure with altitude.