millibars

Millibars, abbreviated mbar, are a unit of pressure defined as one thousandth of a bar. This makes 1 mbar equal to 0.001 bar, or 100 pascals. The millibar is numerically identical to the hectopascal (hPa), since 1 hPa equals 100 pascals. In meteorology and atmospheric science, mbar and hPa are commonly used interchangeably for measuring atmospheric pressure.

In practical terms, a bar is a large unit of pressure; 1 bar equals 1000 mbar. Standard atmospheric pressure at sea level is defined as 1013.25 mbar (or 1013.25 hPa). Weather maps and forecasts have historically used mbar to label surface pressure, though the SI-derived hPa is increasingly preferred in official contexts. Typical atmospheric pressure at sea level ranges roughly from about 970 mbar to 1050 mbar, with deviations indicating high- or low-pressure systems.

Measurement of millibars is carried out with barometers, including aneroid and digital pressure sensors. In modern practice, many instruments report pressure in hPa, aligning with the SI framework, but the term millibar remains widely recognized in meteorology and in historical datasets. In summary, millibars are a legacy yet still prevalent unit for atmospheric pressure, closely tied to the SI hectopascal and the pascal-based system used in scientific contexts.