Altimeter pressure units
Altimeter settings and atmospheric pressure can be expressed in inches of mercury, hectopascals, millibars or kilopascals. U.S. aviation commonly uses inches of mercury, while hPa is common internationally and in meteorology.
inHg and hPa
One inch of mercury is about 33.864 hectopascals. Standard sea-level pressure of 29.92 inHg corresponds to approximately 1013.25 hPa.
Millibars and hectopascals
For practical pressure reporting, 1 millibar equals 1 hectopascal. A pressure of 1013 mb is therefore the same numerical pressure as 1013 hPa.
Kilopascals
One kilopascal equals 10 hPa. Standard sea-level pressure is about 101.325 kPa. Kilopascals appear more often in engineering contexts than in cockpit altimeter-setting use.
30.00 inHg in hectopascals
An altimeter setting of 30.00 inHg is approximately 1,016 hPa. Conversions are useful when comparing weather products, but pilots should enter the setting in the unit required by the installed altimeter and operating procedure.
Pressure setting affects indicated altitude
An incorrect altimeter setting changes indicated altitude. That is why this is not merely a unit-conversion issue: using the wrong number or wrong unit can create a meaningful altitude error.
Pressure altitude is different
Pressure altitude is the altitude indicated when the altimeter is set to standard pressure, commonly 29.92 inHg or 1013.25 hPa. It is a derived altitude used in performance and flight-level contexts, not just another pressure unit.
Related PilotDesk guides
Pressure altitude · Density altitude · Aviation weather