Other than stretching entities with the mouse, I cannot find anywhere to see or edit the sizes numerically. I really want to edit multiple selected entities at the same time, eg to make them all the same width. This seems to be a very basic function, so I must be missing something?
Data Architect does not have a method to change height and width of entities by specifying specific measurements. The content within the entities is typically quite variable (name lengths, # attributes, etc) so most modelers use the ability to "fit" entity size to match the contents.
However, what you can do is display and enable a "snap to grid", which is set in the Diagram and object display options. You can specify grid size. The grid background will assist you to visually compare when manually resizing the entities.