milibar

The milibar (mb) is a unit of pressure used mainly in meteorology. It equals one-thousandth of a bar, or 100 pascals, and is equivalent to the hectopascal (hPa). Historically, mb was the standard unit for atmospheric pressure in weather reports and on pressure charts.

In practice, many meteorological agencies have gradually moved to using the hectopascal or the pascal, especially in SI contexts; nonetheless, the millibar remains common in weather maps and forecasts. In aviation and meteorology, measurements are frequently described in mb on charts, though hPa is used in modern data files.

1 bar = 1000 mb; 1 atm = 101325 Pa = 1013.25 mb; sea level standard pressure is defined as 1013.25 mb (or 1013.25 hPa). Typical atmospheric pressures: low-pressure systems around 980–1000 mb; high-pressure around 1020–1030 mb.

The term "milibar" is used in some languages; English uses "millibar" or "mb" as a symbol. SI favors "hectopascal" (hPa) with 1 hPa = 100 Pa. The millibar remains a legacy unit in many meteorological datasets.