Description & Suggested Solutions
If the Units Management has units turned off ( Edit-->Preferences-->Units), then these voxels are arbitrarily sized.
Turning Spatial Units on in Units Management would rescale all loaded data to the working units.
These are also set in the Units Management, but can usually only be adjusted when no data have yet been loaded.
Upon loading data, if the voxel size is unknown, you can request Amira-Avizo to prompt with a crop editor to adjust the voxel or bounding box size relative to the working units.
The alternative is to load data and then adjust the size using the crop editor.