What is a Millibar?

The millibar equals exactly 100 pascals and is the legacy meteorology unit, identical to the modern hectopascal (hPa). Most weather services worldwide transitioned from millibars to hectopascals in the late 20th century, but the unit persists in aviation weather reports, marine forecasts, and older barometric instruments. Standard sea-level atmospheric pressure is 1,013.25 mbar (or hPa). Hurricane and typhoon central pressures are reported in millibars: a major Category 5 hurricane like Hurricane Andrew (1992) had a central pressure of about 922 mbar. The millibar relates to the hectopascal (1 mbar = 1 hPa exactly), the bar (1,000 mbar = 1 bar), the pascal (100 Pa = 1 mbar), and the atmosphere (1,013.25 mbar = 1 atm). Despite the official preference for hPa, the millibar is retained in some traditional contexts and older texts.

Visual reference for how the millibar relates to other pressure units. Each row links to the full converter for that pair.

• Weather reports and atmospheric pressure
• Altimetry and aviation
• Historical weather records

• ✓1 mbar = 1 hPa = 100 Pa.
• ✓Weather reports: "1013 hPa" and "1013 mbar" mean the same thing.
• ✓Hurricane strength correlates with central pressure drop.

• ✗Confusing mbar and bar — 1000× difference.
• ✗Using mbar for industrial pressures — too small.
• ✗Mixing hPa and mbar in casual writing without noting they are equal.