You can dimension arc walls or other arc elements to obtain the overall length of the wall. 
- Click Annotate tab Dimension panel Dimension panel  (Arc Length). (Arc Length).
- On the Options Bar, select a snap option. 
  For example, select Wall faces to have the cursor snap to the inside or outside wall face. The snap option aids in selecting the radial point. 
   
- Place the cursor on the arc, and click to select the radial point. 
- Select the end points of the arc, and move the cursor up and away from the arc. 
  Note: If the arc ends for the arc length dimension are not visible or selectable, use intersecting reference planes to place the dimension. 
	  
 
- Click to place the arc length dimension.