Converting Atmospheres to Millibars

This example problem demonstrates how to convert the pressure units atmospheres (atm) to millibars (mbar). Atmosphere originally was a unit related to the air pressure at sea level. It was later defined as 101325 pascals. The bar is a pressure unit defined as 100 kilopascals and 1 millibar is 1/1000 bar. Combining these factors gives a conversion factor of 1 atm = 1013.25 mbar.

Problem:

The air pressure outside a cruising jet liner is approximately 0.227 atm. What is this pressure in millibars?

Solution:

1 atm = 1013.25 mbar

Set up the conversion so the desired unit will be cancelled out. In this case, we want atm to be the remaining unit.

pressure in mbar = (pressure in atm) x (1013.25 mbar/1 atm)
pressure in mbar = (230/1013.25) mbar
pressure in mbar = 230 mbar

Answer:

The air pressure at cruising altitude is 230 mbar.