In a METAR, how are altimeter settings expressed?

In a METAR, altimeter settings are expressed in inches of mercury (inHg). This conventional measurement is widely used in aviation, especially in the United States, where altimeter settings are crucial for pilots during takeoffs and landings at airports. These settings help pilots ensure accurate altitude readings necessary for safe flight operations.

While other options like millibars and hectopascals are valid units for measuring atmospheric pressure, they are typically used in meteorological reports and not specifically for altimeter settings in METARs. Feet of mercury is also a standard measurement but is not used in METAR reporting. Thus, the preference for inches of mercury in this context is essential for maintaining consistency and clarity in aviation operations.