Danny McClung sent us this tip on finding the area of nonclosing objects. The easiest way to find the area of an arc is to draw a line from endpoint to endpoint, join the line to the arc with the pedit command, and list the arc for the area. Just remember to undo back to remove the line.

Notes from Cadalyst Tip Patrol:  This tip may seem obvious, but I feel it can be useful.  There are many ways to get your work done in AutoCAD.  Finding the area of an object can be difficult if that object is not closed.  Closing that object is one way, and then take the new object’s area.  All closed objects have an area.  That means you can also find the area of a hatch.  Figure out which way works best for you and the situation you are in.
Tested in AutoCAD 2009