What are the standard units of measure for an altimeter setting?

The standard units of measure for an altimeter setting are inches of mercury. Specifically, altimeters are calibrated to assess atmospheric pressure at sea level, and this measurement is commonly expressed in inches of mercury (inHg).

This unit originates from the mercury barometer, where atmospheric pressure can be measured by the height of a column of mercury. In aviation, this standard unit allows pilots to calibrate their altimeters accurately, ensuring that they maintain correct altitude readings during flight operations relative to the atmosphere's pressure.

Using inches of mercury as the standard enables consistency across aviation practices and ensures that pilots have a reliable means to convert atmospheric pressure into altitude, crucial for safe navigation and operations in varying weather conditions.