Atmospheres
The atmosphere (atm) is a unit of pressure being equal to 101,325 pascals. It is based on the average atmospheric pressure at sea level on Earth.
Millibar
A millibar (mb) is a metric unit of pressure equal to 100 pascals, or one hectopascal. Standard atmospheric pressure at sea level is 1,013.25 millibars, and weather forecasts quote air pressure in them.