Decide how many battens you would like on that wall (this is the general spacing do you want them every 2 feet, every foot). Now divide the length of the wall by the general spacing.
Now in order to have 5 spaces you will need 6 battens, so 5 spaces + 1 equals the number of battens you will need. (*You cannot forget the origin point or the “0” if you will, see the diagram above.)
You cannot forget the thickness of your batten’s themselves. Let’s say they are 3″ so multiply the number of battens (6) by the width of the battens (3″) which is 18″.