If it is a simple shape you could use inquiry area (Tools- Inquiry- Area or area in command line)
You have to basically draw an outline around the edge. If it is a polyline or a rectangle or something like that (not a block though) then you can type in "O" for object at the beginning of the command to just select the object once.
The area will show up on the command line when you end the command.
Other than that I don't know of another command.