Units of Atmospheric Pressure

There are many units of pressure and each are used differently.

• Millibar (mb) - used to label isobars (lines of constant pressure) on a weather map
• Hectopascal (hPa) or Pascal (Pa) - the preferred scientific measurement
• Inches of Mercury (in. Hg) - used by aviators and commonly by meteorologists to talk about the pressure at the surface

Standard value of atmospheric pressure at sea level is: 1013.25 mb = 1013.25 hPa = 29.92 in. Hg