Convert Millibar to Inch of Mercury (mbar → inHg)

Converting millibars to inches of mercury is straightforward: multiply by the conversion factor. Follow these three steps to do it by hand or in your head.

1. 1
   Take your value in millibars

   Start with the number of millibars (mbar) you want to convert.
2. 2
   Multiply by 0.02953

   The conversion factor from mbar to inHg is 0.02953. Multiply your value by this number.
3. 3
   Read the result in inches of mercury

   The result is your value in inches of mercury (inHg).

Multiply the value in millibars by 0.02953. For the reverse direction, multiply by 33.86389.

• ✓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.

What is the 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.

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

What is the Inch of Mercury?

The inch of mercury equals exactly 25.4 mmHg (or about 3,386.4 pascals) and is the American aviation standard for altimeter settings and historic barometer readings. Pilots set their altimeters to the local atmospheric pressure in inHg before takeoff and landing — standard 'sea-level pressure' is 29.92 inHg. American weather reports historically used inHg before transitioning to millibars/hPa, and home barometers in the US still display inHg. The unit relates to the mmHg (25.4 mmHg = 1 inHg), the millibar (1 inHg ≈ 33.864 mbar), the kilopascal (1 inHg ≈ 3.386 kPa), and the psi (1 inHg ≈ 0.491 psi). Aviation's continued use of inHg in the United States reflects regulatory tradition rather than scientific advantage; international ATC outside the US uses hectopascals.

• US aviation altimeter QNH settings
• US residential barometers
• US weather forecasts (older)