How is altitude typically expressed?

Altitude is typically expressed in feet, especially in aviation contexts. This convention is rooted in the history of aviation and is widely accepted in flight operations, air traffic control, and pilot training. Using feet allows for a clear and consistent understanding of altitude among pilots, air traffic controllers, and other aviation professionals.

Feet provide a practical measurement for operations in the lower altitudes where planes operate, particularly in regions like North America, where most altimeters are calibrated in feet. This standardization minimizes confusion and enhances safety within the aviation system. While other units such as miles or kilometers may be used in different contexts, feet remain the primary unit for expressing altitude in aviation.