Definition
The standard sea level atmospheric pressure value of 1,013.2 millibars (mb), used as the international reference pressure for the standard atmosphere. It is equivalent to 29.92 inches of mercury ("Hg) and represents the average weight of the atmosphere pressing down on the surface at sea level under standard conditions.
Plain English
It's the agreed-upon "normal" air pressure at sea level. Aviation, weather, and instrument calibrations all start from this number as the baseline.
Context Anchor
Seen in atmospheric pressure, altimeter setting, and standard atmosphere discussions.
Derivation
A millibar is one-thousandth of a bar. The bar comes from the Greek baros, meaning "weight" — the same root as barometer. So 1,013.2 mb is literally 1,013.2 thousandths of a "weight" unit of air pressure.
Why Pilots Care
It is the reference value used to calculate pressure altitude and to set the altimeter for accurate height readings.
Analogy
It is like saying the same distance in miles or kilometers. The number changes because the unit changes, but the pressure being described is the same.
Grounding Statement
Imagine the entire column of air above a point at sea level on a standard day — its weight pressing down equals 1,013.2 mb.
Intuition Check
Do not read 1,013.2 mb as an altitude, temperature, or weather code. It is a pressure value, and “mb” means millibars.
Example Sentence 1
Standard sea level pressure is 1,013.2 mb, which is the same as 29.92 inches of mercury.
Example Sentence 2
Pressure drops steadily from 1,013.2 mb at sea level to roughly 226 mb at flight level 300.