To change the measurement units of a project:

• That does not have GCPs but has image geolocation.
• That has GCPs.
  
  

A project that does not have GCPs but has image geolocation 

To get the measurements in feet, the suitable output coordinate system needs to be defined. There are the following options:

• Select a Known Coordinate System that uses feet (International Foot or U.S. Survey Foot). For more information: Menu Project > Select Output Coordinate System.... In this case all measurements will be in feet and the outputs will be georeferenced in a known coordinate system.

 

Important: The selected coordinate system must be a known system for the area to be mapped. For example, if the area is located in central Colorado, the system should be NAD83 / Colorado Central (ftUS).

• Select an Arbitrary Coordinate System, setting the unit to feet (ft). For more information: Menu Project > Select Output Coordinate System.... In this case all measurements will be in International Feet.
  
  

A project that has GCPs

Make sure that the GCPs are in a coordinate system that uses feet (International Foot or U.S. Survey Foot). To set the correct coordinate system for the GCPs: How to select / change the Image / GCP / Output Coordinate System.